Extent of aminoglycoside interference in the pyrogallol red-molybdate protein assay depends on the concentration of sodium oxalate in the dye reagent.

brane to ensure that the sample has wicked down the membrane properly. Lastly, the manufacturer recommends that the analysis be performed on urine concentrated to a total protein concentration of 15–20 g/L. In the case of the sample described above, urinalysis demonstrated the presence of 443 leukocytes, 162 erythrocytes, and 3 epithelial cells per high-power field. The presence of debris associated with these cellular elements may account for the sediment observed by the technologist, possibly accounting for interference with the wicking of the urine onto the microporous membrane applicator. By correlating the electrophoretic findings of urine with the total protein, we were able to avoid a false negative. Such comparisons have been recommended by Umbreit and Wiedemann (2 ). However, in more subtle cases, a small monoclonal free light chain could have been missed. Therefore, in addition to comparing all urine electrophoresis results with the total protein concentration, we recommend use of a clear supernatant when particulate matter is present in urine samples and examining the edge of the microporous membrane applicator to be certain that the urine has migrated to its edge.