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Detection of low-molecular-weight proteins in urine by dipsticks
Michael Pugia1, David J Newman, John A Lott
1Diagnostic Business Group, Bayer Corporation, Elkhart, IN, USA.
Background:
Testing of urines with dipsticks for proteinuria, glycosuria, etc., is common practice. A deficiency with currently available dipsticks is their lack of chemical sensitivity and underestimation of low-molecular-weight proteins such as light chains.
Methods:
We experimented with a number of dyes that gave an easily recognized color change on dipsticks for various low-molecular-weight proteins such as alpha-1-glycoprotein, alpha-1- and beta-2-microglobulin, and kappa and lambda light chains. We were successful in formulating a dye for impregnating dipsticks that gave a color change with low-molecular-weight proteins.
Results:
Most dipsticks will measure proteins down to about 1 g/l. Our composite of two dyes (described here as the "TPR" dipsticks) gave reproducible results for protein concentrations of >/=300 mg/l, and detected low-molecular proteins. The TPR reagent is resistant to interferences from many compounds; also, the protein results are not altered in a given urine at a pH between 5 and 8.
Conclusions:
We have developed a dipstick that detects low-molecular-weight proteins. The dipsticks are easy to use and are suitable for outpatient or point-of-care testing. The precision of the dipsticks is satisfactory and is only marginally lower than quantitative spectrophotometric methods using pyrogallol red (PYR).