Pathological Casts in Urinalysis
Introduction to Pathological Casts
- 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
- 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
- Fatty Casts contain lipid droplets and are associated with nephrotic syndrome 2
- Waxy Casts represent advanced tubular damage and are associated with chronic kidney disease 2
- Granular Casts are formed from the breakdown of cellular casts, indicating tubular damage 2
Clinical Correlation and Diagnostic Value
- The presence of pathological casts alongside other urinary findings, such as significant proteinuria, strongly suggests glomerular disease 1
Diagnostic Approach
- 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 significant proteinuria 1
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
- Repeat urinalysis may be necessary to monitor disease progression or response to treatment 1
Classification and Clinical Significance of Urinary Casts
Definition and Classification
- The American College of Rheumatology criteria for lupus nephritis classify granular casts as cellular casts, while waxy casts represent a distinct category of pathological casts indicating advanced tubular damage 3, 4
- The American College of Rheumatology defines cellular casts to include mixed casts, which are explicitly listed as cellular 3, 4
- The revised ACR criteria define "active urinary sediment" to include greater than 5 RBC/hpf and greater than 5 WBC/hpf (in absence of infection) 4
- The American College of Rheumatology criteria limit "cellular casts" to RBC or WBC casts only for diagnostic purposes, though granular casts remain included in the broader classification criteria 3