CBQCA assay of primary amine losses during hemodialysis

Nitrogen loss during hemodialysis is an important issue since all steps taken to improve clearance of urea will also increase loss of amino acids and other normally recyclable sources of nitrogen. Most dialyzers exclude albumin and other proteins, which react well with dyes commonly employed to measure protein, but do allow passage of mono- and oligopeptides that go undetected in protein assays. The CBQCA reagent provides a highly sensitive assay of primary amines that will detect amino acids, low molecular weight polypeptides, and high molecular weight proteins. We collected dialysate using a split stream technique from 28 chronic dialysis patients. With bovine albumin as the standard, the CBQCA assay reported 24.3+/-9.8 g albumin-equivalents (mean+/-S.D.) per dialysate whereas a Coomassie blue assay measured 1.19+/-0.78 g. The CBQCA assay values were substantially higher than previously reported amino acid losses. The CBQCA fluorescent assay for amines provides a simple assay for quantifying primary amine losses in dialysate fluid.