Urinalysis
Basic Information 
Possible Complications and Common Errors to Be Avoided
• Dipstick analysis in horses is only accurate for pH, glucose, protein (except in alkaline urine), pigment, and bilirubin. Dipsticks should not be used to assess specific gravity or presence of white blood cells. Ketones are rarely detected in equine urine.
• pH: Equine urine is normally alkaline (7.0–9.0). Vigorous exercise or bacteriuria can lead to acidic urine. Bacteria can break down urea with urease and produce ammonia, which has a characteristic odor. Feeding concentrates decreases urine pH toward neutral. Foals with dilute urine have a neutral pH that is free of crystals. Aciduria is typically attributed to metabolic acidosis. Dehydrated or anorectic horses may have aciduria. Patients with hypochloremic metabolic alkalosis may have paradoxic aciduria due to an underlying hypokalemia or whole-body potassium deficit.
• Proteinuria: Urine reagent strips can give false-positive results for protein when testing alkaline urine. Proteinuria is assessed more accurately by a chemistry analyzer (<100 mg/dL protein is normal). Measurement of urine protein/creatinine ratio (UP/UCr) is recommended to remove the effects of urine concentration. A ratio greater than 2 : 1 suggests proteinuria, which may be due to exercise, glomerular disease, bacteriuria, or pyuria. Protein-losing glomerulopathies lead to a loss of albumin rather than globulins. Severe chronic renal disease can result in hypoproteinemia and hypoalbuminemia, but this is very rare in horses compared with other species. Hyperglobulinemia consistent with chronic inflammatory response is more common in inflammatory or infectious renal disease.
• The renal threshold for glucose is approximately 160 to 180 mg/dL. Hyperglycemia (150–175 mg/dL) occurs secondary to stress, sepsis, exercise, pituitary adenoma, or diabetes mellitus and can result in glucosuria. Glucosuria can occur after administration of α2 agonists, exogenous corticosteroid therapy, or glucose-containing fluids and parenteral nutrition. If glucosuria exists without hyperglycemia, suspect primary tubule dysfunction (Fanconi syndrome).
• Pigmenturia or blood on reagent strips reflects hemoglobin, myoglobin, or erythrocytes. To differentiate, assess plasma for hemolysis, muscle enzyme activity to distinguish myoglobinuria from hematuria or hemoglobinuria, and urine sediment for the presence of erythrocytes. Fewer than five erythrocytes should be seen per high power field (hpf). Hematuria can be due to inflammation, infection, neoplasia, toxemia, or intense exercise.
• Bilirubinuria is associated with intravascular hemolysis, hepatic necrosis, and obstructive hepatopathies. Hemolysis and hepatic disease are detected by abnormally elevated serum bilirubin concentrations, and increased hepatic enzyme activity is present with liver disease.
• Casts consist of sloughed tubular cells and Tamm-Horsfall glycoprotein. Presence of casts indicates tubular damage, inflammation, or infection.
• More than 10 leukocytes/hpf is associated with infectious or inflammatory disease. Normal equine urine has few to no bacteria, but the absence of bacteria does not rule out infection.
• Equine urine is normally rich in crystals; the majority are calcium carbonate. Calcium phosphate and occasionally calcium oxalate crystals are also found.
• Urine specific gravity measures urine concentration but is determined more accurately by urine osmolality because large molecules such as glucose and protein lead to overestimation of urine concentration using specific gravity.
Normal horses have urine specific gravity of 1.025 to 1.050 and urine osmolality of 900 to 1200 mOsm/kg (three to four times more than serum).
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