Total protein determination in urine: elimination of a differential response between the coomassie blue and pyrogallol red protein dye-binding assays.
BACKGROUND
The total protein content of urine is a good index of renal function, but its determination is unreliable. Protein dye-binding assays are simple, but they characteristically lack a uniform response to different proteins.


METHODS
We investigated a differential response of the Sigma Microprotein Coomassie Brilliant Blue (CBB) and Pyrogallol Red-molybdate (PRM) protein dye-binding assays to urine, using human albumin, albumin/globulin, or urinary protein as calibrator.


RESULTS
The urine protein values (n = 60) obtained with the CBB assay were 110-13 500 mg/L (mean, 2390 mg/L) compared with 160-18 300 mg/L (mean, 3470 mg/L) obtained with the PRM assay (CBB:PRM protein concentration ratio, 0.46-0.88, mean, 0. 69 +/- 0.10). The differential response was highly reproducible as indicated by Sigma urine control Level 1 (within-day CBB:PRM ratio, 0.68 +/- 0.02; between-day CBB:PRM ratio, 0.67 +/- 0.04) and Sigma urine control Level 2 (within-day CBB:PRM ratio, 0.60 +/- 0.01; between-day CBB:PRM ratio, 0.59 +/- 0.02). The use of urinary protein as a calibrator (rather than human albumin) greatly improved the agreement between the assays when applied to urine (y(CBB) = 0. 972x(PRM) - 16 vs y(CBB) = 0.685x(PRM) + 17). In studies using urine controls, this calibrator also improved agreement between the CBB, PRM, trichloroacetic acid (TCA), and benzethonium chloride protein methods and, to a lesser extent, agreement with the TCA-Ponceau S method.


CONCLUSIONS
The use of a urinary protein calibrator improves the agreement between different methods used to determine total protein in urine.
Marshall
T
T
Analytical correspondence. Fax 44-191-515-3747, USA. tom.marshall.sunderland.ac.uk
Williams
K M
KM
D000418:Albumins / Q000032:analysis; D002138:Calibration; D004396:Coloring Agents; D005916:Globulins / Q000032:analysis; D006801:Humans; D011506:Proteins / Q000032:analysis*; D011748:Pyrogallol / Q000031:analogs & derivatives*; D011933:Reagent Kits, Diagnostic; D012394:Rosaniline Dyes; D014508:Urea / Q000737:chemistry
D000418:Albumins; D004396:Coloring Agents; D005916:Globulins; D011506:Proteins; D011933:Reagent Kits, Diagnostic; D012394:Rosaniline Dyes; D011748:Pyrogallol; C058731:pyrogallol sulfonphthalein; C048139:Coomassie blue; D014508:Urea