Testing for Urine Hemosiderin
Urine hemosiderin is tested by microscopic examination of urinary sediment using Prussian blue (iron) staining to detect hemosiderin-laden granules or cells, typically performed when intravascular hemolysis is suspected.
Collection and Preparation
- Collect a fresh urine specimen, ideally a random spot urine sample 1
- The specimen should be processed promptly, as hemosiderin granules can degrade over time 2
- For optimal detection, urine samples may be collected with acidification or appropriate preservatives 1
Laboratory Method
- Centrifuge the urine specimen and examine the sediment microscopically for the presence of hemosiderin granules or hemosiderin-laden cells 2, 3
- Apply Prussian blue (Perls') stain to the urinary sediment, which specifically stains iron-containing hemosiderin deposits blue, making them readily identifiable under light microscopy 2, 3
- Hemosiderin appears as golden-brown to dark brown granules within tubular epithelial cells or free in the sediment on routine microscopy, but Prussian blue staining provides definitive confirmation 3
Interpretation and Scoring
- Absence of hemosiderin granules (score 0) is normal and indicates no significant intravascular hemolysis or microcirculatory overload 2
- A semi-quantitative scoring system can be used: score 1 for 1-3 granules per high-power field, score 2 for 4-6 granules, and score 3 for more than 6 granules per field 2
- The presence of hemosiderin in urine (hemosiderinuria) is characteristic of intravascular hemolysis, as seen in paroxysmal nocturnal hemoglobinuria (PNH), and is not typically found in extravascular hemolysis conditions 4
Clinical Context
- Hemosiderinuria testing is particularly useful when evaluating suspected intravascular hemolysis, such as in PNH, where free hemoglobin is filtered by the kidneys and iron is deposited in renal tubular cells 4, 3
- This test can also detect microcirculatory overload in conditions like chronic venous insufficiency, where erythrocyte diapedesis and extravascular hemolysis occur 2
- The test has high diagnostic accuracy (95%) with excellent sensitivity (94%) and specificity (91%) for detecting significant hemolysis-related conditions 2
Important Caveats
- Hemosiderinuria is distinct from hematuria - the presence of intact red blood cells in urine requires different evaluation including assessment for dysmorphic RBCs, red cell casts, and proteinuria to determine glomerular versus non-glomerular sources 1, 5
- Standard urinalysis and dipstick testing do not detect hemosiderin; specific microscopic examination with iron staining is required 2
- Hemosiderin granules are found within renal tubular epithelial cells that have absorbed filtered hemoglobin, processed it, and subsequently been shed into the urine 3