Effect of red blood cell lysis on protein quantitation in hematuric states

To simulate hematuria, blood from healthy volunteers was added to urine samples of varying osmolalities to produce urocrits ranging from 0.01 to 3.0%. Specimens were then analyzed for protein concentration by a method using a combination of 3% sulfosalicylic and trichloroacetic acids. Microscopic hematuria (urocrit of less than 0.05%) was not associated with proteinuria, but gross hematuria often resulted in substantial amounts of protein being detected. In iso- and hypertonic urines, modest elevations in protein concentration (69-97 mg/dl) were detected. Hypotonic urines produced marked proteinuria (1,302-1,863 mg/dl). Urine protein electrophoreses identified hemoglobin as the responsible protein. Isolated hematuria can cause false-positive proteinuria on the basis of RBC lysis and release of hemoglobin into the urine. The diagnostic and prognostic implications of clinical proteinuria in the hematuric patient can be significant. Thus, in a patient with gross hematuria, a urine protein electrophoresis should be accomplished to assess the contribution of hemoglobin to the total protein determination.