Isomorphic vs Dysmorphic RBCs
- Isomorphic RBCs: Uniform biconcave discs—favor urologic source (stone, tumor, cystitis, BPH).
- Dysmorphic RBCs: Misshapen cells from glomerular passage—favor GN; acanthocytes are most specific.
- Thresholds: >5% dysmorphic suggests glomerular; >20% acanthocytes is highly specific.
See companion page: Dysmorphic RBCs for technique and thresholds.
RBC Casts
- Pathognomonic for glomerular bleeding when present; look for concurrent proteinuria.
- Often sparse—scan multiple fields; ensure fresh sediment and proper centrifugation.
RBC casts + AKI = nephrology emergency consideration (RPGN).
Clinical Integration
- Proteinuria: Glomerular pattern when paired with dysmorphic RBCs or casts.
- Clots/terminal stream: Favor urologic source—consider imaging and urology referral.
- Age/risk factors: Smoker >35 with hematuria → prioritize malignancy exclusion.
Always integrate symptoms, vitals, kidney function, and urine protein with microscopy.
Common Pitfalls
- Old specimens distort shape—repeat with fresh sample within 2 hours of collection.
- Over-reliance on dipstick blood without microscopy confirmation.
- Misreading crenated cells from hypertonic urine as dysmorphic.
Avoid: Anchoring on FeNa or dipstick alone—prioritize the sediment.
When to Refer
- Glomerular pattern (dysmorphic RBCs/RBC casts ± proteinuria) → nephrology referral.
- Isomorphic RBCs with risk factors → urology referral and imaging per hematuria guidelines.
- Mixed patterns or persistent hematuria → coordinated nephrology + urology approach.
References & Further Reading
- Hematuria evaluation guidelines and nephrology microscopy references.
- Evidence on acanthocyte specificity for glomerular bleeding.