Chapter 3 · Urine microscopy and interpretation

Urine microscopy findings to report: red blood cells (RBCs), white blood cells (WBCs), casts (hyaline, granular, red cell, white cell — each clinically significant), bacteria, epithelial cells, crystals. A finding of red cell casts is an indicator of glomerulonephritis and must always be reported and flagged. The microscopy result must be correlated with the dipstick result before release.

Chapter 3 · Practical example

Red cell casts — recognising and acting on the emergency

Red cell casts on urine microscopy are pathognomonic of glomerular bleeding and require urgent clinical notification. Missing them has serious clinical consequences.

▲ The situation

A urine microscopy from a 30-year-old patient shows 8 to 12 red cells per high-power field. The scientist has begun writing a microscopic haematuria report.

Reference: ISO 15189:2022 Clause 7.5; Renal Association Guidelines

✓
Good practice

Before authorising, the scientist scans the low-power field systematically for casts. She identifies two red cell casts. She immediately alerts the section head. The report is revised: Microscopic haematuria — 8 to 12 RBC/hpf. Red cell casts identified — consistent with glomerular bleeding. Red cell casts indicate active glomerulonephritis. Urgent nephrology review is recommended. The section head calls the requesting clinician by telephone.

✗
Poor practice

The scientist focuses on the cell count at high power and reports haematuria without scanning for casts. The report: microscopic haematuria, 8-12 RBC/hpf. The clinician manages the patient conservatively. Three months later, the patient presents with hypertension, oedema, and creatinine 280 micromol/L. Renal biopsy confirms IgA nephropathy. The three-month delay resulted in preventable renal deterioration.

● What this means for your practice

Scanning for casts is mandatory when red cells are present on urine microscopy. Red cell casts require systematic examination at low power across the cast field — they are not visible at high power and can be missed if not specifically sought. A result that fails to report red cell casts when they are present is clinically incomplete.