What are pathological casts in urinalysis?

Pathological Casts in Urinalysis: Clinical Significance and Diagnostic Implications

Pathological casts in urinalysis are specialized cylindrical structures that form in the renal tubules and indicate underlying kidney disease or dysfunction, representing more significant clinical concern than benign hyaline casts. 1

Types of Pathological Casts and Their Significance

Cellular Casts

• Red Blood Cell (RBC) Casts: Indicate glomerular bleeding and are diagnostic of glomerulonephritis 2
• White Blood Cell (WBC) Casts: Suggest pyelonephritis, interstitial nephritis, or inflammatory glomerular disease 2, 3
• Epithelial Cell Casts: Represent tubular epithelial cell sloughing, indicating acute tubular injury 3

Granular Casts

• Formed from the breakdown of cellular casts, indicating tubular damage 2
• More pathologically significant than hyaline casts, suggesting ongoing renal tubular injury 3

Waxy Casts

• Represent advanced tubular damage and are associated with chronic kidney disease 2
• Often seen in end-stage renal disease and severe acute kidney injury 3

Fatty Casts

• Contain lipid droplets and are associated with nephrotic syndrome 2
• Indicate significant proteinuria and podocyte damage 3

Disease-Specific Casts

• Light-chain Casts (Myeloma Casts): Pathognomonic for cast nephropathy in multiple myeloma, appearing as waxy to granular matrix surrounded by reactive, syncytial giant cells 4
• Vacuolar Casts: Associated with advanced proteinuric glomerulopathies, characterized by nonpolarizable, clear vesicles within the cast matrix 5

Clinical Correlation and Diagnostic Value

• Pathological casts provide crucial diagnostic information about the location and nature of kidney injury 3
• Nephrologist-performed urinalysis is significantly more accurate in identifying pathological casts compared to standard laboratory analysis (Kappa for casts: 0.026) 3
• The presence of pathological casts alongside other urinary findings (proteinuria >1g/day) strongly suggests glomerular disease 1

Diagnostic Approach When Pathological Casts Are Identified

• Comprehensive urinalysis with microscopic examination should assess the number and types of casts per field 1
• Serum creatinine and estimated GFR should be evaluated to assess renal function 1
• 24-hour urine collection for protein quantification is recommended if dipstick shows ≥1+ proteinuria 1
• Kidney biopsy may be indicated when specific pathological casts are identified, especially with declining renal function 3

Special Considerations

• Hyaline casts alone can be physiological, but when present in increased numbers (≥2+) even with normal renal function, may correlate with elevated BNP levels and cardiac dysfunction 6
• The presence of mixed casts (hyaline matrix with cellular elements) indicates more severe renal pathology than pure hyaline casts 1
• Proper specimen handling and examination technique significantly impacts cast identification - cytocentrifugation and Papanicolaou staining can improve visualization 7

Follow-up Recommendations

• Patients with pathological casts require monitoring of renal function, proteinuria, and blood pressure 1
• Nephrology referral is strongly indicated when pathological casts are identified, especially with declining renal function 1, 3
• Repeat urinalysis may be necessary to monitor disease progression or response to treatment 1