RBC Morphology in Urinalysis - Glomerular vs Urologic

⭕ Isomorphic RBCs

Uniform biconcave discs

Suggests: Urologic source

Stones, tumors, cystitis, BPH, trauma

🔴 Dysmorphic RBCs

Misshapen from glomerular passage

Suggests: Glomerular source

Glomerulonephritis—acanthocytes most specific

📊 Diagnostic Thresholds

>5%

Dysmorphic RBCs
Suggests glomerular

>20%

Acanthocytes
Highly specific for GN

>80%

Dysmorphic
Strong GN indicator

🚨 RBC Casts: The Pathognomonic Finding

RBC casts are pathognomonic for glomerular bleeding when present. They contain dysmorphic RBCs trapped in a Tamm-Horsfall protein matrix, proving the red cells originated in the kidney.

Key Points:

Often sparse—scan multiple fields. Ensure fresh sediment and proper centrifugation.

⚡ Clinical Pearl

RBC casts + AKI = Nephrology Emergency

Consider RPGN and initiate urgent workup including complements, ANCA, and anti-GBM.

🔗 Clinical Integration

Proteinuria Present	Strengthens glomerular pattern diagnosis
Clots/Terminal Stream	Favor urologic source—consider imaging + urology
Smoker >35 + Hematuria	Prioritize malignancy exclusion

Always integrate: Symptoms, vitals, kidney function, and urine protein with microscopy

⚠️ Common Pitfalls

✗

Old specimens distort shape—repeat within 2 hours

✗

Over-reliance on dipstick blood without microscopy

✗

Misreading crenated cells from hypertonic urine

✗

Anchoring on FeNa instead of the sediment

📋 Referral Guidance

→ Nephrology

Glomerular pattern: Dysmorphic RBCs, RBC casts ± proteinuria

→ Urology

Isomorphic RBCs with risk factors (age >35, smoking, gross hematuria)

→ Both

Mixed patterns or persistent hematuria—coordinated approach

📚 References

Hematuria evaluation guidelines • Nephrology microscopy references • Evidence on acanthocyte specificity for glomerular bleeding

🔬 UA Overview 🧫 Dysmorphic RBCs 📚 Interpretation 🔎 Ancillary Testing

🩸 RBC Morphology in Urinalysis