Characteristics of binding between reagent-strip indicators and urinary proteins.

We describe the binding characteristics of two indicator dyes that are widely used in commercial "dip-stick" indicators for protein in urine. Binding was studied by both gel filtration chromatography and by spectrophotometric titrations. The results demonstrate that the well-known lack of sensitivity of these strips to proteins other than albumin relates to the number and affinity of binding sites on these proteins as compared to albumin. The data suggest that these test strips can screen more effectively for albuminuria than for other proteinurias.