# 🩸 RBC Morphology in Urinalysis

### ⭕ 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

\>5%

Acanthocytes\
Highly specific for GN (Kohler 1991)

\>80%

Dysmorphic\
Strong GN indicator

### 🚨 RBC Casts: A Strong Diagnostic Clue

RBC casts **strongly support a glomerular source of bleeding** in the appropriate setting. They contain red cells trapped in a uromodulin (Tamm–Horsfall protein) matrix. They do not identify the immune cause, and their absence does not exclude glomerulonephritis.

**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

### 📚 Sources

1.  **Köhler H, Wandel E, Brunck B.** Acanthocyturia — a characteristic marker for glomerular bleeding. *Kidney Int.* 1991;40(1):115-120. [PMID: 1921146](https://pubmed.ncbi.nlm.nih.gov/1921146/). *— Foundational paper for acanthocyte specificity in glomerular hematuria; supports the \>5% acanthocyte threshold.*
2.  **Fairley KF, Birch DF.** Hematuria: a simple method for identifying glomerular bleeding. *Kidney Int.* 1982;21(1):105-108. [PMID: 7077941](https://pubmed.ncbi.nlm.nih.gov/7077941/). *— Original phase-contrast paper for dysmorphic RBC differentiation.*
3.  **Muriithi AK, Nasr SH, Leung N.** Utility of urine eosinophils in the diagnosis of acute interstitial nephritis. *Clin J Am Soc Nephrol.* 2013;8(11):1857-1862. [PMID: 24052222](https://pubmed.ncbi.nlm.nih.gov/24052222/). *— Adjacent reference for urine sediment evaluation; sensitivity 30.8%, specificity 68.2% for AIN.*

[🔬 UA Overview](https://urinenephrology.org/2025_UDPA_Lectures_Live/urinalysis/index.html) [🧫 Dysmorphic RBCs](https://urinenephrology.org/2025_UDPA_Lectures_Live/urinalysis/dysmorphic-rbcs.html) [📚 Interpretation](https://urinenephrology.org/2025_UDPA_Lectures_Live/urinalysis/interpretation.html) [🔎 Ancillary Testing](https://urinenephrology.org/2025_UDPA_Lectures_Live/urinalysis/microscopic.html)

For educational purposes only—use local referral guidelines and clinical context.

© 2025 Andrew Bland MD - All Rights Reserved


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