Why Dysmorphic RBCs Matter
- Dysmorphic RBCs—especially acanthocytes—indicate glomerular bleeding.
- They help distinguish GN from urologic sources (stone, tumor, infection).
- They guide urgency: GN patterns warrant expedited workup and often nephrology consult.
Teaching Pearl: RBC casts are pathognomonic but uncommon; dysmorphic RBCs are more sensitive and practical to detect.
Definitions & Thresholds
- Dysmorphic RBC: Misshapen erythrocyte from glomerular passage; spicules/blebs common.
- Acanthocyte (G1 cell): Ring form with vesicle-like blebs—highly specific for glomerular origin.
- Diagnostic Thresholds:
- >5% dysmorphic RBCs suggests glomerular source.
- >20% acanthocytes is highly specific for GN.
Data synthesized from nephrology urinalysis literature and microscopy standards.
Technique
- Use fresh, midstream, clean-catch specimen (ideally examined within 2 hours).
- Phase-contrast microscopy preferred; bright-field acceptable with training.
- Scan low power for casts, then high power for morphology quantification.
If unavailable, partner with a lab using phase-contrast or send to a nephrology microscopy service.
Specificity, Sensitivity, and Pitfalls
- Specificity: Acanthocytes are highly specific; dysmorphia alone less so.
- Sensitivity: Improves with fresh samples and phase-contrast technique.
- Pitfalls: Prolonged storage, high osmolality, and severe hematuria can distort RBCs.
Avoid: Over-calling dysmorphia in old specimens or after vigorous exercise.
When to Escalate
- Dysmorphic RBCs or RBC casts + AKI/proteinuria → urgent nephrology consult.
- Consider complements and serologies if GN suspected; expedite tissue diagnosis.
- Gross hematuria with clots or terminal stream bleeding suggests urologic source—consider imaging/urology.
See also: GN Overview and RPGN emergency recognition.
Clinical Integration
- Proteinuria + dysmorphic RBCs: Strengthens GN likelihood.
- Hypertension/edema: Supports nephritic syndrome pattern.
- Normal complements: Narrows differential (e.g., IgA nephropathy, ANCA, anti-GBM).
Case tie-in: See Case 22 (RPGN with IgA vasculitis) for real-world application.
References & Further Reading
- KDIGO Glomerular Diseases guideline framework; microscopy best-practice reviews.
- Studies validating acanthocyte thresholds for glomerular hematuria.
- Educational atlases of urinary sediment morphology (phase-contrast).