Automated Urine Sediment Analyzers Underestimate the Severity of Hematuria in Glomerular Diseases

Abstract

Hematuria, either glomerular or extraglomerular, is defined as 3 or more red blood cells (RBCs)/high power field. Currently, urinalyses are commonly performed using automated urine sediment analyzers. To assess whether RBC counting by automated urine sediment analyzers is reliable for defining hematuria in glomerular diseases, random specimen urinalyses of men with nephritic glomerular diseases (7,666 urinalyses) and bladder cancer (12,510 urinalyses) were retrospectively reviewed. Urine RBCs were counted by an automated urine sediment analyzer based on flow cytometry (UF-1000i, Sysmex Corporation) or digital image analysis (Cobas 6500, Roche Diagnostics GmbH). In about 20% of urine specimens, the specific gravity was less than 1.010, making the RBC counts unreliable. In the urine specimens with specific gravity ? 1.010, RBC counts measured by either UF-1000i or Cobas 6500 were well correlated with the positive grades in the dipstick blood test. However, at a trace, 1+, or higher positive dipstick tests for blood, RBC counts were graded significantly lower in glomerular diseases than in bladder cancer. The findings suggest that RBC counting by UF-1000i or Cobas 6500 underestimates the severity of hematuria in glomerular diseases, possibly because dysmorphic RBCs in glomerular diseases are susceptible to hemolysis and/or fail to be properly recognized.