(1)
Office of Research and Development, United States Environmental Protection Agency, Washington DC, USA
Abstract
The three diagnosis chapters—Hematology, Clinical Chemistry, and Urinalysis—are intended to be the most informative and most used parts of this handbook. There is a lot of useful information packed into these chapters. Once animal clinical pathology data have been evaluated and anomalous values for several parameters have been identified, these chapters can help one ascertain what these anomalies signify. Next to the name of each parameter are its common abbreviations. For each parameter, there are listings for organs that may be affected, specimen handling information, and supportive tests that may be used to confirm a diagnosis. These are followed by a brief description of the parameter including its strengths and weaknesses and other need-to-know information. Next to up and down arrows are potential diagnoses for when a parameter’s value is increased or decreased. When there is a name for an increase or decrease (e.g., hypersthenuria or hyposthenuria), that is also provided. Diagnosis information is provided for 13 urinalysis tests.
The primary function of the kidneys is the excretion of metabolic waste products (urea, electrolytes, creatinine, hemoglobin, hormone byproducts) and other toxic chemicals from the blood stream. The kidneys are key to whole-body homeostasis including the regulation of blood pH to within a very narrow range, arterial pressure, blood volume, and water and electrolyte levels. It should not be surprising that 22 % of an animal’s cardiac output goes to the renal arteries when at rest. The kidneys also produce several hormones. Most notably, kidneys undergoing hypoxia release erythropoietin (EPO) to stimulate the bone marrow to produce more erythrocytes. The character of urine is the result of three renal functions:
Glomerular filtration—A passive process regulated mainly by arterial hydrostatic pressure. Substances with molecular weights >68,000 g/mol (e.g. cells, lipoproteins, and most proteins) cannot pass through the glomerulus.
Tubular Reabsorption—Useful compounds (e.g. glucose, water, electrolytes, amino acids, and vitamins) are efficiently reabsorbed from the glomerular filtrate by the renal tubules.
Tubular Secretion—Body homeostasis is maintained by the secretion of water, electrolytes and other substances in the renal tubules.
Time, alkalinity, bright light, acids, alkalis, moisture, medication, and high temperatures can result in faulty urinalysis measurements. Urine stored in the urinary bladder for several hours may differ from freshly-formed urine with respect to pH, cells, casts, crystals, and bacterial growth. The pH of stored urine increases (i.e., becomes more alkaline) due to urease-producing bacteria and the escape of dissolved CO2. Alkalinity promotes lysis of blood cells and casts, and may also affect crystals. Cell lysis can occur in urine with a specific gravity of <1.008. Ideally, samples should be analyzed within 30 min. Urinary nitrates from dietary metabolites are converted to nitrite by bacteria in the urinary tract. A bacterial infection can result in elevated nitrite levels.
Urine content is affected by diet, water intake, activity, and body temperature. Morning urine is more concentrated, and is more likely to contain cells, casts, and abnormal constituents, but it is unaffected by activity or feeding. Normal urine can range from clear to dark yellow. Darker urine is usually, but not always, more concentrated. Some foods can affect the color of urine, such as carrots, blackberries, beets, and rhubarb. Drugs that can color urine include chloroquine, iron supplements, levodopa, riboflavin, nitrofurantoin, phenazopyridine, phenothiazines, phenytoin, and triamterene. Turbidity or cloudiness indicates the presence of crystals, cells, mucus, bacteria, casts, or fluids from the reproductive tract. Cat urine tends to be cloudy because of the presence of lipid droplets. Test strips are a simple way to evaluate multiple parameters including specific gravity, pH, protein, glucose, ketone, bilirubin, urobilinogen, leukocytes, nitrite, and hemoglobin.
Acetoacetic Acid
See Ketones
Acetone
See Ketones
Appearance
See Color and Turbidity
Beta-Hydroxybutyric Acid
See Ketones
Bile Pigments
See Bilirubin
7.1 Biliburin [Bili]
Affected Organs: Liver, RBCs, marrow.
Specimen Handling: Fresh random urine may be stored 24 h at 4 °C away from light.
Supportive Tests: Serum conjugated bilirubin, ALT, ALP, AST, bile acids, GGT, 5′-NT.
Bilirubin is the breakdown product of hemoglobin. The form of bilirubin found in urine is conjugated (direct) bilirubin. It is water-soluble and able to pass freely through the glomerulus without being reabsorbed. Unconjugated (indirect) bilirubin is not found in urine. When freshly voided urine is shaken, a yellow-green or brown foam indicates the presence of bilirubin. Normal urine has a lesser white foam when shaken.
The concentration of urinary conjugated bilirubin reveals the extent of intra- and extrahepatic biliary tract obstruction. The liver may be markedly diseased before bilirubinuria occurs. Urinary bilirubin should always be compared with serum bilirubin levels. Serum hyperbilirubinemia typically precedes bilirubinuria but not in dogs.
Bilirubin is not typically found in the urine of horses, pigs, or sheep; but it is found in the urine of cats with liver disease. It is normal for cattle and some dogs to have mild bilirubinuria. Urine exposed to light may give a false-negative reading because of photoconversion to biliverdin. If measurements cannot be made within 30 min, samples should be refrigerated in the dark. Bilirubinuria is rare in cats.
↑ | [Bilirubinuria] |
Intrahepatic and extrahepatic biliary tract obstruction, increased serum conjugated bilirubin, hepatitis, hepatocellular damage (progressed), abnormal RBC destruction, starvation, fever, feline leukemia | |
Phenothiazines (large doses), salicylates, blood transfusions | |
↓ | Ascorbic acid, nitrites |
Blood Pigments
See Hemoglobin
Clarity
See Turbidity
Cloudiness
See Turbidity
7.2 Color
Affected Organs: Kidneys, pancreas, adrenals.
Specimen Handling: Fresh random urine is used. Urine should be evaluated quickly since color can change on standing.
Supportive Tests: Turbidity, specific gravity, serum conjugated bilirubin, ALT, ALP, AST, bile acids, GGT, 5′-NT.
The color of urine can be affected by many things including diet, fluid balance, diseases, and medicines. Normal urine color may range from very pale yellow (practically colorless) to dark amber depending on the amount of yellow urochromes it contains. While urine tends to be pale when diluted and dark when concentrated, this is not always the case. The only sure way to gauge urine concentration is by measuring specific gravity. Abnormal colors of red or green may denote the presence of blood, bile pigments, pigmented drugs, or their breakdown products. Urine may change colors on standing. Cloudy urine, due to mucus and calcium carbonate, is pathologic except in horses. Cat urine is darker when it has jaundice. Normal rabbit urine ranges from yellow to red/brown. Ferrets have dark urine that interferes with colorimetric techniques.
Pale yellow—Urine is diluted and typically has a low specific gravity due to increased water consumption, diabetes mellitus, diabetes insipidus, toxic nephrosis (diuretic phase), nephrosis, advanced amyloidosis, hyperadrenocorticism, pyelonephritis, primary renal glucosuria, pyometra; IV fluids, administration of corticosteroids or ACTH.
Dark yellow—Urine has high levels of yellow urochromes, usually has a high specific gravity, and is concentrated due to dehydration, fever, toxic nephrosis, terminal renal disease, low blood pressure, circulatory dysfunction.
Bright yellow—Vitamin B supplements.
Yellowish brown (foams on shaking)—Bilirubin and urochrome.
Deep brown/black—Blood, hemoglobin (urine is translucent), myoglobinuria, melanin from malignant melanoma.
Red/brown—Hemoglobin (urine is translucent), hematuria (RBCs in urine cause urine to be cloudy), myoglobinuria (urine is translucent), food dyes (carrots, blackberries, beets, rhubarb), phenolphthalein, phenothiazine, azosulfamide, urates, bile, drug metabolites.
Green/blue—Oxidation of bilirubin to biliverdin in poorly preserved specimens, drug metabolites, methylene blue, acriflavine, dithiazanine iodide.
White cloud—Excessive oxalic acid and glycolic acid in urine.
7.3 Glucose [GLU, Gluc]
Affected Organs: Pancreas, kidneys, adrenals.
Specimen Handling: Urine should be stored in a dark container on ice. It can be stored 24 h when mixed with 5 mL of glacial acetic acid or 5 g of sodium benzoate or sodium fluoride. The sample should be measured at room temperature. Interferences: ascorbic acid, bilirubin, ketones, fluoride, or formaldehyde.
Supportive Tests: Serum glucose, ALT, ALP, AST, bile acids, 5′-NT, urobilinogen, BUN, creatinine, lipase, amylase, glucose, Ca.
Glucose should be nonexistent in urine. Glucose readily passes through the glomerulus but is completely reabsorbed in the proximal tubules, even when the kidneys are damaged. Colorometric test strips are typically used to detect and quantify glucose. Faulty colorometric measurements can result from the presence of ascorbic acid in dog urine, bilirubin, ketones, fluoride, or formaldehyde.
NOTE: Glucose is also measured in serum or plasma; see Chap. 6, Clinical Chemistry Diagnosis.
↑ | [Glucosuria, Glycosuria] |
Kidney disease or damage, impaired renal tubular reabsorption, high carbohydrate diet, increased blood glucose, uncontrolled diabetes mellitus, acute pancreatitis, hyperthyroidism, chronic liver disease, milk fever in ruminants, adrenal cortical hyperplasia, fear, excitement, restraint | |
I.V. glucose therapy | |
Corticosteroids, ACTH, D-thyroxine, morphine, glucagon, diuretics, penicillin, tetracycline, streptomycin, chlortetracycline, chloramphenicol, lactose, maltose, pentose, ascorbic acid, salicylates, EDTA, lead | |
↓ | Not clinically significant |
7.4 Hemoglobin [Hb, HGB, Hgb]
Affected Organs: Blood, kidneys, skin.
Specimen Handling: Fresh random urine should be examined immediately. The lysing of RBCs in urine can lead to erroneous results.
Supportive Tests: BUN, creatinine, erythrocyte morphology (ghost cells), urine pH, CBC.
Hemoglobinuria, an increased level of hemoglobin in the urine, typically indicates a systemic disease or poisoning that results in intravascular hemolysis. It should not be confused with hematuria, which is blood in the urine due to genitourinary tract disease. Still, RBCs in dilute or alkaline urine can lyse, releasing their hemoglobin and leaving behind ghost erythrocytes.
NOTE: Hemoglobin is also measured in blood; see Chap. 5, Hematology Diagnosis.
↑ | [Hemoglobinuria] |
Intravascular hemolysis, hematuria, pregnancy, extensive burns, autoimmune hemolytic anemia, transfusion reactions, kidney infarction, thrombotic thrombocytopenia, purpura (bruises), bacillary hemoglobinuria (in cattle, sheep, and occasionally dogs) | |
Sulfonamides, quinine, phenylhydrazine, hemolytics | |
Copper poisoning, fava beans, poisonous snakes and spiders | |
↓ | Not clinically significant |
Ketone Bodies
