- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
BASICS
- Analysis of urine as an aid in the diagnosis of disease via visual inspection, dipstick analysis, refractometry or osmometry, and microscopy of sediment
- Urine is collected by free catch during voiding or by urethral catheterization
- Cystocentesis is not a method of urine collection in horses. Voided urine samples are easily contaminated. Catheterization is preferred for bacteriologic examination
- Urine appearance changes during urination, especially toward the end of micturition (more crystals)
- Urine volume and composition influenced by feed and water intake, salt supplementation, environmental factors, exercise stress, systemic disease, and drug administration
- Visual inspection—color ranges from pale yellow to dark tan (may turn brown/red color after prolonged storage or exposure to air). Cloudy/turbid from large quantities of calcium carbonate (some calcium oxalate and phosphate). Viscous from the presence of mucus. Urine often appears red on snow or shavings
- Dipstick—alkaline pH, typically 7.0–9.0 (foals pH 5.0–7.0). Negative glucose; negative/trace protein; negative ketones; negative bilirubin; positive urobilinogen
- Osmometry—osmolality is the most accurate determinate of solute concentration of urine; typically 1500 mOsm/kg
- Refractometry—USG measured with a refractometer estimates solute concentrations
- Urine concentration classified as hyposthenuric (USG <1.008; osmolality <269 mOsm/kg); isosthenuric (USG 1.008–1.014; osmolality 260–300 mOsm/kg); hypersthenuric (USG >1.014; osmolality >300 mOsm/kg)
- Microscopy of sediment—refrigerate sample; must be evaluated within 1 h or cells/casts deteriorate, crystals dissolve/form. Method of collection can affect analysis; catheterization may result in mild trauma, increasing urine protein and RBCs
- Abundant calcium carbonate crystals, small numbers of calcium oxalate and phosphate crystals
- No epithelial casts
- RBCs <5 cells/hpf, WBCs <5 cells/hpf, small numbers of bacteria on voided sample (contamination)
- USG of foal urine should be <1.008 with osmolality <250 mOsm/kg. This reflects a normal high-volume milk diet
- Kidneys determine body water content and ion composition
- Important components of this regulation include renal blood flow, glomerular filtration, tubular modification of glomerular filtrate
- Blood is filtered by the glomeruli in the kidneys. Small solutes are freely filtered at the glomerulus. The renal tubules extensively modify the ultrafiltrate by reabsorbing or secreting solutes
- Urinary bladder stores urine for elimination through the urethra
- Milk diet (foals)
- Psychogenic polydipsia
- Diabetes insipidus
- AKI—nephrotoxic drugs (e.g. NSAID, aminoglycosides, tetracycline), prolonged hypoperfusion, pigment nephropathy, toxicities (e.g. cantharidin, red maple leaf), leptospirosis, neoplasia, glomerulonephritis
- CRF—prolonged AKI
- Myoglobin (e.g. polysaccharide storage myopathy, exertional rhabdomyolysis, immune-mediated myositis)
- Hemoglobin (intravascular hemolysis, e.g. piroplasmosis, neonatal isoerythrolysis in foals, immune-mediated hemolytic anemia)
- RBCs (e.g. idiopathic renal hematuria, pyelonephritis, cystitis, neoplasia, trauma)
- Methemoglobin (e.g. toxicities—red maple leaf, onion, turnip, kale, garlic)
- Bilirubin (e.g. hepatic disease, cholestasis)
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS