Chapter 7 Evaluation of Renal Function

 

 

 

                          

  7.1 INTRODUCTION:

The main responsibility of the kidneys is the regulation of the internal environment of the body. The kidneys accomplish this by:

• 1. Elimination of excess body water
• 2. Elimination of inorganic elements
• 3. Elimination of nonvolatile end products of metabolic activity
• 4. Retention within the body of substances required for the maintenance of normal functions (amino acids, hormones, vitamins, plasma proteins, glucose, etc.)
• 5. Elimination of certain foreign toxic substances
• 6. Formation and excretion of substances such as hydrogen ions and ammonia.

Therefore, the kidneys play an important role in the regulation of water balance, electrolyte balance, acid/base balance, maintenance of osmotic pressures of body fluids and in the removal of metabolic waste products and other toxic substances. The effectiveness of this regulation is directly related to renal blood flow rate, glomerular filtration and renal tubular excretion and reabsorption; therefore, renal function tests are directed toward the measurement of these factors in order to determine the nature of an impairment of renal function. As with the measurement of the function of any organ, the value of renal function testing is limited by the techniques available, the accuracy of testing, the frequency of testing, the reserve capacity of the kidney, and species variability. Renal function tests do not reveal the definitive cause of disease, whether the disease is in an acute or chronic stage and the reversibility of the lesion. 

7.2 GENERAL CONSIDERATIONS:

A. Purpose of renal function tests

• 1. Determine the nature of an impairment of renal function
  • a. Urinalysis is usually the only test that provides diagnostic assistance.
  • b. Because of the tremendous reserve capacity of the organ, only in the case of severe renal disease (>50% non-functioning nephrons) is it possible to detect abnormal function.
• 2. Determine the extent of an impairment of renal function. It is best to perform serial tests to determine the extent that an abnormal kidney function is reversible or to follow the course of chronic kidney impairment.
• 3. Renal function tests provide part of the evidence upon which a prognosis should be based. Serial determinations, rather than single tests, are more reliable for purposes of prognosis.

B. Desirable characteristics of tests for glomerular function

• 1. The rate of glomerular filtration serves to assess glomerular function.
• 2. To measure the rate of filtration it is necessary to use a substance which:
  • a. Can be measured in urine and plasma
  • b. Can pass the glomerular membrane
  • c. Must not be reabsorbed or excreted by the tubules to any appreciable degree.

C. Desirable characteristics of tests for tubular function

• 1. To measure the rate of tubular excretion it is necessary to use a substance which:
  • a. Can be measured in urine and plasma
  • b. Has little or no glomerular filtration or tubular reabsorption
  • c. Is predominantly removed from blood plasma by tubular excretion
• 2. To measure the reabsorptive ability of the tubule it is necessary to use a substance which:
  • a. Can be measured in urine and plasma
  • b. Can pass through the glomerular membrane and is largely reabsorbed by the tubules (Glomerular function must simultaneously be measured)
  • c. Has little or no tubular excretion

D. Renal function tests in common use for clinical purposes fall into the following categories:

• 1. Urine specific gravity and the ability of the kidney to concentrate or dilute urine.
• 2. Estimations of nonprotein nitrogen levels in the blood.
• 3. Dye excretion tests.
• 4. Renal clearance tests.
• 5. Miscellaneous blood chemistry tests. 

7.3 SPECIFIC RENAL FUNCTION TESTS : (See Table VII.1)

7.3.1 Urine Concentration Tests

1. Water Deprivation (Fishburg Concentrate)

• a. Withholding water for a period of time causes plasma hyperosmolality and pituitary release of antidiuretic hormone (ADH). ADH acts on the renal tubular epithelial cells causing reabsorption of water thereby increasing urine specific gravity. If the tubules are nonfunctional, water will not be reabsorbed and the specific gravity will remain low.
• b. The water deprivation test is indicated when repeated random samples of urine have a specific gravity in the isosthenuric range (1.008-1.012).
• c. Contraindications include:
  • 1) Uremia - a diagnosis of renal disease is already established.
  • 2) Debilitated animals
  • 3) Dehydration. Maximal stimulation for ADH release is already in effect. If the specific gravity is below 1.25 in conjunction with dehydration the tubules have reduced concentrating ability.
• d. Procedures
  • 1) Withhold water for 12-24 hours or until the animal loses 5% of its body weight (never exceed this amount of weight loss).
  • 2) Empty the bladder at 12 hours and determine the urine specific gravity. If it is above 1.020 discontinue the test because the animal can concentrate urine.
  • 3) If the specific gravity remains below 1.020, continue water deprivation for a total of 24 hours (not exceeding a 5% body weight loss). If the specific gravity remains below 1.020 at this point, an impairment of concentrating ability is present.
• e. Failure of concentrating ability occurs with:
  • 1) Renal disease
    • a) Approximately 2/3 of the nephrons are nonfunctional before concentrating ability is reduced.
    • b) Decreased concentrating ability usually occurs before increased BUN or creatinine. An exception is in the early stage of primary glomerular disease (glomerulotubular imbalance).
  • 2) Diabetes insipidus
    • a) Pituitary disease causes a lack of ADH secretion. The renal tubules are normal but are not stimulated to reabsorb water.
    • b) The specific gravity is usually in the 1.001-1.006 range because the animal can reabsorb solute.

2. Vasopressin Test (Pituitrin Concentration Test, Pitressin Concentration Test)

• a. The test is similar to the urine concentration test except exogenous ADH (pitressin) is administered in place of water deprivation.
• b. Indications
  • 1) When the water deprivation test is abnormal to differentiate between diabetes insipidus and renal disease.
  • 2) May be used in place of the water deprivation test to evaluate tubular reabsorption when prolonged water deprivation is contraindicated.
• c. Contraindications
  • 1) uremia
  • 2) pregnancy
• d. Procedures (dog)
  • 1) Inject SubQ 1/4 unit of pitressin tannate/kg body weight (up to 5 units).
  • 2) Empty bladder at 30 minutes
  • 3) Check urine specific gravity at 3, 6, and 9 hours
  • 4) A specific gravity remaining at less than 1.020 is abnormal.
• e. Interpretation
  • 1) Concentration to a specific gravity of 1.020 or greater indicates diabetes insipidus if preceded by a negative urine concentration test.
  • 2) Failure to concentrate to a specific gravity of 1.020 indicates renal disease.

7.3.2 Tests for Nonprotein Nitrogen Blood Levels

Determination of the nonprotein group of nitrogenous substances, especially urea and creatinine, is important because significantly increased values are usually the result of accumulation of these substances in the blood because of defective kidney elimination.

1. Blood Urea Nitrogen

• a. Urea is the principal end product formed by the liver from protein catabolism (urea cycle).
• b. It is excreted almost entirely by the kidney.
  • 1) Urea appear in the glomerular filtrate in the same concentration as the blood. This is a process of simple filtration and does not require energy. Diminished glomerular filtration causes high BUN concentration.
  • 2) Urea may passively diffuse with water from the tubular lumen back into the blood. At the highest flow rate, this reabsorption is approximately 40%. If urine flow is decreased, more is reabsorbed (up to 60%) adding to the blood urea concentration.
• c. Methods
  • 1) Azostix
    • a) stick impregnated with urease that changes color when in contact with urea in the blood.
    • b) may be used to semiquantitate BUN concentration, but the method is not accurate
  • 2) Quantitative colorimetric methods
  • 3) Urography
    • a) semiquantitative method
    • b) chromatographic test strip banded with different reagents
      • (1) 1st band - contains an excess of the enzyme urease. When the urease comes in contact with the urea in the sample, the urea is converted to an ammonia salt which migrates up the paper.
      • (2) 2nd band - contains potassium carbonate which frees ammonia from the ammonia salt. This free ammonia is then forced into the atmosphere of the reagent tube where it drops to the bottom of the tube and then builds up. A plastic barrier above the 2nd band prevents further migration of the serum or plasma.
      • (3) 3rd band - contains an indicator bromocresol green in tartaric acid. When free ammonia comes in contact with the bottom of the band, it neutralizes the acid. This produces a color change, the height of which bears a direct relationship to the amount of ammonia released.
  • (4) Procedure:
    • - Place 0.2 ml of serum or plasma in a 10X75 mm test tube. (Sample should be placed at the bottom of the tube without wetting the sides of the tube).
    • - Place one urograph paper with the taped end down in the center of the tube.
    • - Allow it to stand at room temperature for 30 minutes.
    • - At the end of 30 minutes compare the indicator band on top of the urograph paper with the standardized chart. No color indicates less than 10 mg/dl urea.
    • - The urograph will only measure concentrations between 10 and 75 mg/dl. For samples over 75 mg/dl, a dilution with normal serum may be used.
• d. Interpretation of increased BUN concentration (azotemia) - normal BUN is from 10-30 mg/dl.
  • 1) Prerenal azotemia
    • a) Increased protein catabolism secondary to intestinal hemorrhage, necrosis, infection, fever, and corticosteroids may cause a mild increase.
    • b) Decreased renal perfusion (reduced glomerular filtration) can cause azotemia (usually under 100 mg/dl) and occurs with shock, dehydration, congestive heart failure, vomiting, diarrhea.
    • c) Very high protein diet.
  • 2) Renal azotemia
    • a) Approximately 75% of the nephrons must be nonfunctional.
  • 3) Postrenal azotemia
    • a) May be caused by anything which might prevent the urine from passing out of the urinary tract, thereby permitting the urea nitrogen to be reabsorbed back into the blood stream.
    • b) Calculi or prostatic hypertrophy

2. Creatinine

• a. Creatinine is a nonprotein nitrogenous substance formed during muscle metabolism of creatin and phosphocreatin.
• b. It is excreted by glomeruli filtration and significant quantities are neither excreted nor reabsorbed by the tubules; therefore, it is a rough index of the glomerular filtration rate (GFR).
• c. Creatinine excretion by the kidney is fairly constant and is not affected by diet, exercise, fever, etc.
• d. It is eliminated by the kidney much easier than urea nitrogen, therefore, an increase in creatinine is not seen as early as an increase in urea nitrogen during renal involvement.
• e. Methods for measuring creatinine are generally colorimetric e.g., alkaline picrate method of Jaffee).
• f. Interpretation:
  • 1) Normal values range from 1 to 2 mg/dl
  • 2) Low values have no significance
  • 3) Increased values occur in:
    • a) Primary renal disease with reduced GFR
    • b) Impaired renal blood flow
    • c) obstruction of urinary system
  • 4) Creatinine may be helpful in making a prognosis. Phillips in Colorado states that if creatinine is between:
    • a) 1-2 mg/dl and BUN is 50 - prognosis is excellent
    • b) 2-5 mg/dl and BUN is elevated - prognosis is good
    • c) 5-7 mg/dl and BUN is elevated - prognosis is guarded
    • d) greater than 7 mg/dl - animal will probably die

7.3.3 Dye Excretion tests - The most commonly used dye is Phenosulfonphthalein

1. Phenolsulfonphthalein (PSP)

• a. When PSP is injected IV most of the dye (approximately 95%) is bound to albumin and excreted by the tubules; therefore, it is a measure of tubular function.
• b. The small amount not bound to albumin is filtered by the glomerulus.
• c. This test appears to be most applicable for an assessment of kidney function in the canine species.
• d. Two methods can be used (dog):
  • 1) Excretion Test
    • a) Inject 6 mg of dye IV after the bladder has been emptied (catheterization).
    • b) After 20 minutes the contents of the bladder are gently aspirated with a syringe and all urine is collected in a flask.
    • c) After dilution and mixing with sodium hydroxide the quantity of dye excreted is measured spectrophotometrically (560 nm) or by visual comparison with color standards.
    • d) Normal dogs can excrete 21 to 66 percent of the dye in 20 minutes.
  • 2) Clearance Test
    • a) Inject 1 mg/kg body weight IV.
    • b) Measure blood levels at 30 or 60 minutes following injection.
    • c) This is very useful during acute nephritis since only a small amount of urine is being produced.
• e. Interpretation
  • 1) Renal disease
    • a) Approximately 2/3 of the nephrons are nonfunctional before an abnormal value results.
    • b) Although PSP is a measurement of tubular excretion, at the dosage used (which is not the tubular maximum), it is principally a test of renal plasma flow.
  • 2) Reduced renal perfusion (shock, dehydration, or cardiovascular disease) results in less dye delivered to the kidney per period of time; thereby, increasing the clearance time.

7.3.4 . Renal Clearance Tests

• 1. In theory, a substance may be excreted by:
  • a. Glomerular filtration alone
  • b. Glomerular filtration plus tubular excretion
  • c. Glomerular filtration plus tubular reabsorption
  • d. Tubular excretion alone
• 2. The manner by which a substance is excreted by the kidney directly affects its renal clearance rate.
  • a. If a substance is completely filtered at the glomerulus and completely reabsorbed by the tubules, its clearance value is zero (e.g., glucose)
  • b. As the degree of tubular reabsorption diminishes, the substance may appear in the urine, increasing its clearance (e.g., urea)
  • c. If there is no reabsorption of a substance then its clearance will be equivalent to the rate of glomerular filtration (e.g., inulin and creatinine)
  • d. If in addition to being filtered through the glomerulus, the substance is also excreted by the tubular epithelium, its clearance will exceed the rate of glomerular filtration by an amount equal to the extent of tubular excretion (e.g., phenol red)
• 3. The maximum limit of renal clearance is determined by renal blood flow.
• 4. Sulfanilate Clearance (dog)
• a. Sodium sulfanilate is eliminated from the blood primarily by glomerular filtration and is therefore a method of evaluating glomerular filtration.
• b. A T1/2 for clearance is calculated from blood samples collected at intervals over a 90-minute period after IV injection of sodium sulfanilate at a dosage of 20 mg/kg of body weight.
• c. This test is suggested to be of value in detecting decreases in renal function before development of azotemia.

7.3.5 Miscellaneous Blood Chemistries

1. Electrolytes

• a. Potassium - removed from plasma by active reabsorption in the proximal tubules and is then actively excreted by cells of the distal tubules.
• b. Sodium - ability to retain sodium is frequently lost in the presence of generalized chronic renal diseases characterized by polyuria.
• c. Bicarbonate - with advanced renal disease, loss of bicarbonate may occur.
• d. Phosphate - most of the phosphate excretion by the kidney is by glomerular filtration, with a variable amount of reabsorption by the tubules. Hyperphosphatemia occurs with chronic progressive and generalized acute renal disease because as the GFR is reduced, the kidney loses its ability to eliminate phosphorus.
• e. Calcium - hypocalcemia may be observed with chronic generalized disease. Hypercalcemia is frequent in horses with renal disease (glomerulonephritis) and is usually accompanied by a hypophosphatemia.

2. Nonelectrolytes

• a. amylase - normally removed from plasma by renal excretion
• b. blood pH - metabolic acidosis is a consistent finding in patients with renal failure.

Figure VII.I: Kidney Function Tests

7.5 URINALYSIS 

Whenever an evaluation of renal function is needed, the first step should be a routine analysis. The urine affords one of the most valuable aids to diagnosis known to the practitioner and its examination should never be omitted in an obscure illness. A urine analysis is not a short cut to a diagnosis. Urine analysis, in order to be thorough and of practical value, must be physical, chemical and microscopic. Chemical examination, although of great importance, can never alone lead to a dependable diagnosis. Only through the microscope can the nature of the disease in the genito-urinary tract, as well as its exact location, be revealed.

The Kidney Performs Two Major Tasks:

• 1. The elimination of wastes which result from body metabolism or from introduction of foreign substances into the body.
• 2. The conservation or excretion of normal constituents in the plasma, so that the concentration of substances in the blood is maintained within limits consistent with health. 

Most irritants reach the kidney via the general circulation. This means that their effects may be felt first in the renal corpuscles and next in the tubules.

The kidneys act in three ways to maintain the constant composition of the blood.

• First, the capillaries of the glomeruli function as filters for water and also for constituents of the blood plasma which can pass through the capillary wall by dialysis. The fluid which passes through this membrane contains all the constituents of the blood plasma except the colloids and water which they are able to hold back.
• Secondly, as fluid passes down the convoluted tubules, substances that are needed in the blood are reabsorbed by the epithelial cells and returned to the capillaries around and between them.
• Thirdly, the epithelial cells of the tubules apparently form and secrete some substances such as ammonia and hippuric acid. They also concentrate and excrete pigments.
• Injuries to the glomeruli and to the tubules may change these functions. When the permeability of the glomerular capillary tuft is increased due to irritation, albumin appears in the urine. Albumin further increases in tubular epithelial degeneration. Loss of albumin from the blood reduces the colloidal osmotic pressure, which in turn results in generalized edema. Edema is not due to loss of albumin alone, but also to a generalized increase in permeability of capillaries, which is caused by irritation.

A complete urinalysis includes physical, chemical and microscopic examination of the urine. 

7.5.1 PHYSICAL EXAMINATION

7.5.1.1 Quantity of Urine

• 1. Normal - varies with food and water intake, climate and exercise
• 2. Abnormal
  • a. Increased amount (polyuria)
    • 1) Chronic interstitial nephritis - the kidney cannot concentrate urine
    • 2) Diabetes mellitus - strong osmotic activity of glucose in the distal tubules of kidney does not allow water to be removed normally and diuresis occurs
    • 3) Diabetes insipidus- deficiency of antidiuretic hormone (ADH) from posterior pituitary
    • 4) Absorption of large serous effusions and exudates
    • 5) Pyometra - produces polydipsia and polyuria
    • 6) Diuretics - cause rapid formation of urine
    • 7) Excessive fluid intake
      • a) parenteral injection
      • b) orally - known as psychogenic water consumption
  • b. Decreased amount (oliguria)
    • 1) Acute interstitial nephritis
    • 2) Reduced fluid intake
    • 3) Dehydration from any cause
    • 4) Gastrointestinal disorders with vomiting and diarrhea
    • 5) Fever
    • 6) Exercise
    • 7) Cardiac decompensation - interferes with renal circulation

7.5.1.2 Color

• 1. Color or urine is dependent upon the presence of urochromes from endogenous metabolic processes and hemoglobin metabolism. The urochromes may be diluted or concentrated depending upon the volume of urine.
• 2. Interpretation
  • a. Pale yellow to yellow brown - normal color due to urochromes
  • b. Colorless to pale yellow (usually low specific gravity and polyruia except in diabetes mellitus)
    • 1) Chronic interstitial nephritis
    • 2) Diabetes mellitus (polyuria with a normal to high specific gravity)
    • 3) Diabetes insipidus
    • 4) Excessive intake of water or fluids
    • 5) Pyometra - in some cases
    • 6) Hyperadrenocorticism
    • 7) Amyloidosis
    • 8) Generalized nephritis and pyelonephritis
  • c. Dark yellow to yellow brown (concentrated urine with a high specific gravity and oliguria)
    • 1) Acute nephritis
    • 2) Decreased fluid intake
    • 3) Dehydration
    • 4) Fever
    • 5) Prolonged vomiting or diarrhea
  • d. Yellow brown to greenish yellow (bile pigments and urobilinogen usually produce a greenish foam when shaken)
  • e. Red, wine or brown
    • 1) Cloudy - hematuria
    • 2) Translucent - hemoglobinuria
  • f. Brown to brownish black
    • 1) Normal horse urine is yellow when voided, but turns a deep brown color upon standing due to oxidation
    • 2) Azoturia - myoglobinuria
    • 3) Methemoglobinuria
    • 4) Melanin in standing urine
  • g. Green
    • 1) Methylene blue
    • 2) Acriflavine
  • h. Red
    • 1) Phenothiazine
    • 2) Phenolphthalein

7.5.1.3 Transparency

• 1. Recorded as:
  • a. Clear
  • b. Cloudy
  • c. Flocculent
• 2. Interpretation

Most of the time urine is clear on being voided, except in the horse when it is normally thick and cloudy due to calcium carbonate crystals and mucus. Material which impart turbidity to the urine are:

• a. Bacteria
• b. Epithelial cells
• c. Erythrocytes (urine pink or red)
• d. Leukocytes
• e. Mucus
• f. Fat
• g. Crystals

7.5.1.4 Foam

• 1. When normal urine is shaken after collection, a small amount of white foam is produced.
• 2. If foam is abundant and slow to disappear, there is a high concentration of protein (proteinuria).
• 3. Bile salts produce a green or yellow foam.
• 4. Hemoglobin foam is red to brown.

7.5.1.5 Odor

• 1. Urine from males of the feline, porcine and caprine species normally has a strong odor.
• 2. A strong ammonia odor may indicate the presence of bacteria, as bacteria convert urea to ammonia.
• 3. A sweet fruity odor is produced by ketone bodies from conditions such as:
  • a. Diabetes mellitus
  • b. Pregnancy ketosis
  • c. Acetonemia

7.5.1.6 Specific Gravity

The specific gravity of urine is a measurement of the relative amount of solids in solution and is an indication of the degree of tubular reabsorption or concentration by the kidney. Under conditions of normal renal function and normal metabolism, the specific gravity varies inversely with the volume of urine excreted. If large volumes of urine are excreted, the specific gravity is usually low, whereas if small quantities are being eliminated, the specific gravity is generally high.

1. Methods of Determination

• a. Urinometer - requires large volume of urine (at least 10 ml)
• b. Refractometer - only one drop of urine is needed

2. Normal Values

3. Interpretation

• a. Decreased specific gravity
  • 1) Chronic interstitial nephritis - usually from 1.003 to 1.015 due to inability of kidney to concentrate the urine.
    • a) A "fixed" specific gravity may result (isosthenuria) and refers to the phase when the specific gravity is fixed between 1.008 and 1.012, which is the same molecular concentration as that of plasma dialysate. It is due to the inability of the kidney to dilute or concentrate the urine beyond these points.
    • b) A water deprivation or concentration test can be used to differentiate chronic interstitial nephritis from low specific gravity due to increased water intake or diabetes insipidus. The results would be as follows:
      • - Normal kidney - S.G. >1.020
      • - Impaired Kidney - the closer the S.G. is to 1.010, the less the amount of functioning kidney
      • - Diabetes insipidus - S.G. may increase, but not to normal range

CAUTION! This test is contraindicated if BUN and creatinine concentrations are increased (uremia) or the patient is already dehydrated.

• 2) Uremia - if advanced
• 3) Diabetes insipidus - S.G. usually from 1.001 to 1.006 due to a deficiency of antidiuretic hormone (ADH) from the posterior pituitary
  • a) Administration of 0.5 to 1.0 ml of posterior pituitary extract will produce immediate, but temporary, cessation of thirst and polyuria.
  • b) Restricting fluids for 12 hours will elevate the specific gravity, but not to normal limits and less urine will be produced.
  • c) With infusion of Ringer's solution, isotonicity will be preserved in both plasma and urine of healthy animals, while hypertonic plasma and hypotonic urine will occur if the animal has diabetes insipidus.
• 4) Diabetes mellitus - sometimes, although increased S.G. is more common
• 5) Pyometra
• 6) Hyperadrenocorticism
• 7) Renal amyloidosis
• 8) Generalized nephritis and pyelonephritis
• 9) Mobilization of effusions or edema fluids
• 10) Fluid therapy
• 11) Administration of ACTH or corticosteroids
• 12) Treatment with diuretics

• b. Increased specific gravity
  • 1) Acute interstitial nephritis - usually from 1.030 to 1.060 due to inability to excrete water
  • 2) Cystitis - products of inflammatory reaction are added to the urine
  • 3) Diabetes mellitus - usually from 1.012 to 1.040, as the glucose in the urine is responsible for the increased specific gravity, despite the polyruia
  • 4) Reduced fluid intake
  • 5) Dehydration
  • 6) Vomiting and diarrhea - if prolonged
  • 7) Hypovolemic Shock
  • 8) Edema associated with circulatory failure
  • 9) Burns
  • 10) Fever
  • 11) High environmental temperature
  • 12) Excessive panting or sweating

NOTE: For each 0.4 gram of protein or 0.27 gram of glucose in the urine, the specific gravity increases by 0.001. 

7.5.2 CHEMICAL EXAMINATION

Chemical evaluation of urine has been made simple through modern technology. Reagents for specific tests are contained on individual pads on a single plastic strip. Urine is placed on the strip and time is allowed for the urine to react with the reagents on each pad. The results are read from a comparative color chart located on the outside label of the bottle of strips. All test results are obtained in less than one minute and are usually reported in a semi-quantitative manner (i.e., negative, trace, 1+ to 4+).

The urine test strips are marketed under names like Multistix, Combistix, BiliLabstix and Uristix. They usually measure pH, protein, glucose, ketones, bilirubin, blood/hemoglobin, and urobilinogen in urine, although other tests are also available.

7.5.2.1 pH

• 1. Normal range varies with species, diet and metabolism. Carnivores have a neutral to acid urine, while herbivores have a neutral to alkaline urine. 
• 2. Normal Values

• 3. Interpretation
  • a. Acid
    • 1) Normal in carnivores
    • 2) Nursing calves and foals
    • 3) Diet with
    • 4)Starvation
    • 5)Fever
    • 6)Acidosis
    • 7)Prolonged muscular activity
    • 8)Administration of acid salts
  • b.Alkaline
    • 1)Normal in herbivores
    • 2)Diet high in roughage or vegetable matter
    • 3)Cystitis
    • 4)Urine retention
    • 5)Rapid absorption of effusions
    • 6)Alkalosis
    • 7)Alkaline therapy

7.5.2.2 Protein

1.Methods

• a.Colorimetric test strip (Ames)
• b.Colorimetric reagent tablet (Ames)
• c.Robert's test
• d.Sulfosalicylic acid test

2.Interpretation

• a.Protein is normally absent or present in only a trace quantity.
• b.Physiological or functional proteinuria is transient and due to a temporary increase in glomerular permeability as a result of congestion of the capillaries. Examples are:
  • 1)Excessive ingestion of proteins
  • 2)Emotional stress
  • 3)Excessive muscular exertion
  • 4)Convulsions
• c.Organic proteinuria
  • 1)Renal proteinuria
    • a)Nephritis - protein from increased permeability of the glomerulus and tubules and from infectious exudates
    • b)Nephrosis - degenerative changes
  • 2)Post-renal proteinuria - protein from contamination by exudates or blood after the urine leaves the renal tubules
    • a)Pyelitis
    • b)Ureteritis
    • c)Cystitis
    • d)Urethritis
    • e)Vaginitis
    • f)Balanoposthitis
    • g)Prostatitis
    • h)Urolithiasis
    • i)Trauma with hemorrhage

7.5.2.3 Glucose

1.Methods

• a.Colorimetric test strip (Ames)
• b.Colorimetric reagent tablet (Ames)
• c.Benedict's test

2.Interpretation

• a.Glucose is normally absent from the urine.
• b.Glucosuria or glycosuria is usually associated with hyperglycemia but not always. The renal threshold for glucose is exceeded and the tubules cannot reabsorb all the glucose from the urine. Tubular damage will also impair glucose resorption.
• c.Causes of glycosuria include:
  • 1)Diabetes mellitus
  • 2)Acute pancreatic necrosis
  • 3)Emotional glycosuria - epinephrine secretion
  • 4)Systemic stress in ruminants - cortisol secretion
  • 5)Hyperthyroidism
  • 6)Hyperadrenocorticism
  • 7)Hyperpituitarism
  • 8)Increased intracranial pressure
  • 9)Shock
  • 10) Chronic liver disease
  • 11) Enterotoxemia
  • 12) General anesthesia
  • 13)Certain drugs (corticosteroids) and glucose solutions
  • 14)Ingestion of excessive carbohydrates
  • 15)Renal glycosuria without hyperglycemia (Fanconi syndrome)

7.5.2.4 Ketones

1.Methods

• a.Colorimetric test strip (Ames)
• b.Colorimetric reagent tablet (Ames)
• c.Ross' test (can also be applied to milk)

2.Interpretation

• a.Ketone bodies include:
  • 1)acetone
  • 2)acetoacetic acid
  • 3)beta hydroxybutyric acid
• b.Ketonuria is present with ketonemia and indicates deficient carbohydrate metabolism. Fats are mobilized for energy, rather than carbohydrates and ketosis results.
• c.Causes of ketosis include:
  • 1)Late pregnancy and lactation, especially in dairy cows
  • 2)Pregnancy toxemia in sheep and goats
  • 3)Diabetes mellitus
  • 4)Acidosis
  • 5)Mild fever (if prolonged)
  • 6)Impaired liver function
  • 7)Infectious diseases causing a caloric imbalance
  • 8)Ether or chloroform anesthesia
  • 9)Starvation or fasting
  • 10)Vomiting and diarrhea (if prolonged)
  • 11)A high fat diet
  • 12)Hyperadrenocorticism
  • 13)Hyperpituitarism
  • 14)Excessive female sex hormones

7.5.2.5 Bilirubin

1.Methods

• a.Colorimetric test strip (Ames)
• b.Ictotest reagent tablet (Ames)
• c.Foam test
• d.Methylene blue test
• e.Gmelin test

2.Interpretation

• a.Normally, the urine of the dog, and occasionally of the cat, may contain small amounts of conjugated bilirubin. Unconjugated bilirubin, being bound to albumin, cannot pass an intact glomerular membrane.
• b.Increased concentrations of bilirubin in the urine indicate an abnormality in hemoglobin-bilirubin metabolism, which may be of prehepatic, hepatic or posthepatic origin.
• c.Causes of bilirubinuria include:
  • 1)Biliary obstruction
    • a)Complete - bilirubinuria without urobilinogen
    • b)Partial - bilirubinuria with urobilinogen
  • 2)Liver disease - bilirubinuria may precede clinical jaundice and is therefore an early indication of liver disease
    • a)Hepatitis
    • b)Hepatic necrosis
  • 3)Hemolysis - excessive hemoglobinemia is toxic to the liver and kidney; when liver damage occurs, jaundice and bilirubinuria result.
  • 4)Acute enteritis
  • 5)Intestinal obstruction

7.5.2.6 .Blood/Hemoglobin

1.Methods

• a.Colorimetric test strip (Ames)
• b.Hematest or Occultest reagent tablets (Ames)
• c.Hemoccult test paper (Schieffelin)
• d.Benzidine test

2.Interpretation

• a.Blood may enter anywhere along the urinary tract. It can result from:
  • 1)Hemorrhage
  • 2)Infection
  • 3)Inflammation
  • 4)Hemoglobin or myoglobin passing through an intact glomerulus
• b.Erythrocytes, hemoglobin and myoglobin will all produce a positive blood reaction. It is of diagnostic significance to be able to differentiate these three conditions.
• c.Hematuria - intact erythrocytes are present in the urine sediment. Causes include:
  • 1)Acute nephritis
  • 2)Nephrosis - marked degeneration
  • 3)Renal infarction
  • 4)Renal passive congestion
  • 5)Neoplasm
  • 6)Urolithiasis
  • 7)Renal abscess
  • 8)Pyelitis
  • 9)Pyelonephritis
  • 10)Ureteritis
  • 11)Cystitis
  • 12)Urethritis
  • 13)Trauma
  • 14)Estrus or post-partum
  • 15)Prostatitis
  • 16)Severe infection - anthrax, leptospirosis, ICH
  • 17)Chemical agents
  • 18)Sweet clover poisoning
  • 19)Thrombocytopenia
  • 20)Parasites
  • 21)Acute vegetative endocarditis
  • 22)Congestive heart failure
  • 23)shock
• d.Hemoglobinuria - none to few erythrocytes are present in the urine sediment. Causes include:
  • 1)Post-parturient hemoglobinuria
  • 2)Bacillary hemoglobinuria
  • 3)Clostridium perfringens Type A
  • 4)Leptospirosis
  • 5)Piroplasmosis/babesiasis
  • 6)Hemolytic disease of newborns
  • 7)Incompatible blood transfusion
  • 8)Photosensitization
  • 9)Severe burns
  • 10)Ingestion of large amounts of beet pulp
  • 11)Chemical agents
  • 12)Toxic plants
• e.Myoglobinuria - urine will be brown to black in color and no erythrocytes are present in the urine sediment. Causes include:
  • 1)Azoturia in the equine (Paralytic equine myoglobinuria, Tying-up syndrome, Monday morning sickness)
  • 2)Exertional rhabdomyolysis in the canine

7.5.2.7 Urobilinogen

1.Methods

• a.Colorimetric test strip (Ames)
• b.Wallace-Diamond method using Ehrlich's reagent

2.Interpretation

• a.Urobilinogen is a chromagen which is formed in the intestine by the reducing action of bacteria on bilirubin. If present in the general circulation, some may enter the kidney to be excreted in the urine. The urine will appear greenish yellow in color.
• b.Normally, urobilinogen is absent in the urine or present in only trace amounts. Its presence indicates that the bile duct is at least partially patent.
• c.Persistent absence of urobilinogen in the urine may be caused by
  • 1)Biliary obstruction
  • 2)Nephritis with polyuria
  • 3)Decreased hemolysis
  • 4)Impaired intestinal absorption (i.e., diarrhea)
  • 5)Antibiotics that affect intestinal bacteria
• d.Increased urobilinogen in the urine can result from:
  • 1)Hepatitis
  • 2)Cirrhosis
  • 3)Hemolytic jaundice

7.5.2.8 Miscellaneous chemical tests on the urine

• 1.Indican/Indole - Obermayer's method
• 2.Chloride - Fantus method
• 3.Calcium - Sulkowitch test
• 4.Sulfonamides - Lignin test

7.6.3 MICROSCOPIC EXAMINATION OF URINE SEDIMENT

7.6.3.1 Introduction

• 1.Microscopic examination of urine sediment is of great clinical importance and should never be omitted.
• 2.For best results, it is essential that the techniques of collection, processing and examination be performed with great care.
• 3.Examination of the sediment should always be made shortly after collection so that:
  • a.Degeneration and lysis of cellular elements will not occur
  • b.Bacteria will not proliferate
• 4.The sediment should be examined for:
  • a.Amount
  • b.Color
  • c.Type or contents
• 5.In health, urine contains only a small amount of sediment. Small numbers of cells and other formed elements from the length of the urogenital tract may be present. These include:
  • a.Epithelial cells from the nephron, ureters, pelvis, bladder or urethra
  • b.Mucus threads and spermatozoa
  • c.A few leukocytes and erythrocytes do reach the urine, probably as a result of diapedesis in any part of the urinary tract.
  • d.Urine from dogs and cats has phosphate crystals, while horse urine has calcium carbonate crystals and mucus threads.
  • e.Extraneous objects such as parasite eggs from fecal contamination, fungal spores, pollen grains and other organic matter may contaminate voided urine.

7.6.3.2 Classification of Sediment

• 1.The sediment may be divided into:
  • a.Organized elements
  • b.Unorganized elements
• 2.Of great clinical value is the examination of the organized fraction of sediment which consists of:
  • a.Epithelial cells
  • b.Leukocytes
  • c.Erythrocytes
  • d.Casts
  • e.Bacteria, yeast, fungi, protozoa, parasite ova and sperm
• 3.The unorganized elements are primarily crystals, pigments and fat droplets.
• 4.Epithelial Cells
  • a.Epithelial cells are normally seen in the urine, but are increased in instances where there is cystitis or inflammation present.
  • b.Large squamous cells are derived from the urethra and vagina.
  • c.Transitional epithelial cells are from the urethra, bladder, ureters or renal pelvis.
  • d.The smaller round to polyhedral cells come from the renal tubules.
  • e.It is very difficult to pinpoint the site of damage from the epithelial cells present in the sediment.
• 5.Leukocytes
  • a.Under normal conditions, only a few white blood cells are present.
  • b.Numerous leukocytes occur only as a result of a pathological process.
  • c.It has been indicated that more than 10 leukocytes per high power field is an indication that inflammation or necrosis of tissue is present in the urogenital tract.
  • d.The presence of leukocytes in the urine constitutes pyuria. The genital tract must also be considered a possible source of these cells.
  • e.If the specimen has been obtained by catheterization or cystocentesis, the leukocytes present must have been derived from either the:
    • 1)Bladder
    • 2)Ureter
    • 3)Pelvis or Kidney
  • f.Diseases in which pyuria is observed include:
    • 1)Nephritis
    • 2)Pyelonephritis
    • 3)Urethritis
    • 4)Cystitis
  • g.Leukocytes may be difficult to distinguish since they are not as well preserved as they are in the blood. Changes include:
    • 1)Degeneration of the nucleus
    • 2)Precipitation of crystals on the cell surface
    • 3)In alkaline urine, cells are usually swollen, ragged in appearance and very granular
• 6.Erythrocytes
  • a.Large numbers suggest inflammation or necrosis
  • b.In addition they might result from:
    • 1)Trauma or rough catheterization
    • 2)Damage to capillaries (certain viral infections)
    • 3)Infarction
    • 4)Hemorrhagic tendencies
    • 5)Violent exercise
  • c.The morphology of the RBCs varies depending upon the specific gravity of the urine.
    • 1)Low S.G. - cells may be ballooned into a spherical shape or may be lysed and become a ghost form
    • 2)S.G. around 1.020 - cell is biconcave disc
    • 3)High S.G. - cells are crenated and have prickles on the surface
  • d.The location of the hemorrhage may be suggested by carefully observing the act of micturition.
    • 1)Blood which appears at the onset of urination may be due to a lesion in the urethra, uterus, vagina, penis or prostate.
    • 2)When the blood is uniform throughout the sample, bleeding is probably from the kidney, bladder or ureter.
    • 3)Blood which appears at the end of urination probably comes from the bladder.
• 7.Casts
  • a.The presence of casts in the urine indicates a pathological change in the kidney. This change may be only slight or transitory.
  • b.Casts form from a combination of protein and mucopolysaccharide.
  • c.The presence of casts denotes that protein has been lost through the glomerulus or possibly from the tubular cells.
  • d.Casts are fairly common in concentrated acid urine, but uncommon in dilute alkaline urine.
  • e.Several types of casts have been described in the urine of domestic animals such as:
    • 1)Hyaline Cast
    • 2)Granular Cast
    • 3)Waxy Cast
    • 4)Epithelial Cast
    • 5)Fatty Cast
    • 6)Blood Cast
    • 7)Leukocyte Cast
• 8.)Bacteria
  • a.Normal urine is bacteria-free in the bladder, but accumulates organisms as it is voided.
  • b.The presence of yeast, fungi, protozoa and parasitic ova is usually a result of contamination.
• 9.Unorganized Sediment
  • a.Plays a minor role
  • b.Ingestion of ethylene glycol may result in oxalate crystals in the urine
  • c.Leucine and Tyrosine crystals indicate severe liver disease due to poisoning from phosphorous, carbon tetrachloride or chloroform

7.8 STUDY GUIDE