Overview

• Abnormally high number of casts (>2–3 casts/lpf) in urine sediment. May develop in dogs or cats with primary kidney disease or systemic disorders that secondarily affect the kidneys.
• High numbers of casts indicate accelerated renal cellular degeneration, glomerular leakage of protein, hemorrhage, or exudation into renal tubular lumens.

Systems Affected

Renal/Urologic

Signalment

Dog and cat

Causes & Risk Factors

Differential Diagnosis

• History of potential exposure to toxins or nephrotoxic drugs-rule out acute tubular necrosis.
• Recent onset of vomiting or diarrhea-rule out renal ischemia caused by dehydration.
• Recent inhalational anesthesia-rule out tubular necrosis caused by ischemia.
• Potential for exposure to infectious diseases-rule out nephritis.
• Fever-rule out infectious, inflammatory, and neoplastic disease.
• Cardiac murmur, especially if diastolic and of recent onset-rule out bacterial endocarditis.
• Petechiae and ecchymoses-rule out systemic thrombosis.
• Cylindruria plus azotemia and adequately concentrated urine (specific gravity 1.030 in dogs and 1.040 in cats)-consider prerenal disorders such as dehydration.
• Cylindruria plus azotemia and inadequately concentrated urine (specific gravity <1.030 in dogs and <1.040 in cats)-consider kidney failure.
• Cylindruria plus leukocytosis-consider infectious and inflammatory disorders.
• Cylindruria plus thrombocytopenia-consider DIC.
• Cylindruria plus glucosuria and proteinuria-consider renal tubular necrosis.

Laboratory Findings

CBC/Biochemistry/Urinalysis

• Epithelial, granular, and/or waxy casts indicate diseases that cause degeneration and necrosis of renal tubular epithelial cells.
• RBC casts indicate severe glomerular disease or hemorrhage into renal tubules.
• WBC casts indicate renal inflammation, most often caused by pyelonephritis; however, most patients with pyelonephritis do not have WBC casts.
• Hyaline casts-associated with disorders that cause proteinuria; also may be observed during diuresis and after dehydration.
• Anemia, hemoconcentration, leukocytosis, or thrombocytopenia in some patients.
• High serum concentrations of urea nitrogen, creatinine, and phosphorus in patients with dehydration or kidney disease.

Other Laboratory Tests

• If the patient has thrombocytopenia or RBC casts, perform coagulation studies (e.g., PTT, PT, FDP, D-dimers) to rule out consumptive coagulopathy such as DIC.
• If the patient has proteinuria, determine urine protein:creatinine ratio to evaluate magnitude of proteinuria.
• If the patient has pyuria or WBC casts, perform urine culture to rule out urinary tract infection.
• If systemic infectious diseases are suspected, submit serum for appropriate titers.

Diagnostic Procedures

Consider renal biopsy if kidney disease persists or progresses and the cause cannot be determined from routine diagnostic tests.

Contraindications

Avoid nephrotoxic drugs.

Patient Monitoring

Physical examination including patient's weight to assess hydration status.

Prevention/Avoidance

Avoid or correct risk factors that predispose to development of exposure of kidneys to toxins and/or renal anoxia.

Possible Complications

Permanent kidney disease depending on underlying cause of cylindruria.

Zoonotic Potential

Possible in patients with leptospirosis. Avoid direct contact with infected urine in these

See Also

Nephrotoxicity, Drug-Induced

Abbreviations

• DIC = disseminated intravascular coagulation
• FDP = fibrin degradation products
• lpf = low power field
• PT = prothrombin time
• PTT = partial thromboplastin time
• RBC = red blood cell
• WBC = white blood cell