Influence of a variable differential function on the stone-growth-related urinary depletion effect.

sodium oxalate without SDS) by varying the concentration of the dye (0.03 or 0.12 mmol/L), sodium oxalate (0 or 2 mmol/L), and SDS (25 or 100 mg/L) in all combinations. For protein assays, we mixed 20 ␮L of sample, calibrator, or water (blank) with 1 mL of PRM reagent and measured the absorbance at 600 nm after 30 min against the blank. The effects of the aminoglycosides on the absorbance readings in the PRM assay (in the absence of protein) with reagents at three different dye concentrations are shown in Table 1. Doubling the concentration of the dye from 0.06 to 0.12 mmol/L increased the absorbance attributable to aminoglycoside by up to 273% (geneticin), whereas halving the concentration (0.03 mmol/L) decreased the absorbance by up to 87% (tobramycin). Doubling the concentration of the dye in combination with addition of SDS and omission of sodium oxalate increased the ami-noglycoside interference by up to 2500% (amikacin). Halving the concentration of the dye and doubling the sodium oxalate concentration (with omission of SDS) eliminated the interference (Table 1). We confirmed the results, using urine control supplemented with aminogly-cosides at the maximum concentrations expected in pa-tients' urines: 0.2 g/L amicakin, gentamicin, neomycin, or tobramycin; 1.0 g/L kanamycin or streptomycin (4, 8, 9). The measured protein concentration in the urine control was falsely increased by neomycin (67% higher), genta-micin (33%), tobramycin (26%), amikacin (9%), strepto-mycin (7%), and kanamycin (6%) when we used the Watanabe reagent but was unaffected by the aminoglyco-sides (respective values Ͻ1%) when we used the modified reagent (n ϭ 4; CV Ͻ6%). In conclusion, the extent of aminoglycoside interference in the PRM assay is dictated by the composition of the dye reagent. SDS increases the interference (6), whereas sodium oxalate decreases the interference (7), and these effects are compounded by changes in the concentration of the dye. Thus, increased dye combined with the omission of sodium oxalate (plus SDS) gives very high interference , whereas decreased dye combined with increased sodium oxalate (minus SDS) eliminates detectable interference. Urinary protein as measured with a Pyrogallol-Red-Molybdate complex manually and in a Hitachi 726 automated analyzer. An improved Pyrogallol Red-molybdate method for determining total urinary protein. interference with the Dade Behring Pyrogallol red-molybdate method for the measurement of total urine protein [Letter]. Aminoglycoside interference in the Pyrogallol red-molybdate protein assay is increased by the addition of sodium dodecyl sulfate to the dye reagent [Letter]. Extent …