Albuminuria estimated from proteinuria in diabetics. Is it a real alternative in clinical practice?

While proteinuria detectable by dip-sticks is the hallmark of overt diabetic nephropathy, urinary albumin excretion (UAE) above normal but Albustix-negative (so-called microalbuminuria) is the main characteristic of the preproteinuric phase of the diabetic renal disease. Reliable measurement of UAE requires very sensitive and accurate methods, such as radioimmunoassay (RIA), which, however, are not suitable for routine UAE analysis. The Coomassie Brilliant Blue dye binding method has been suggested to be a simple and economical way of indirectly measuring albuminuria in diabetic patients. In the present paper, we compared the chemico-clinical characteristics of a RIA method with those of the Coomassie dye binding method, in order to verify if it is really possible to calculate albuminuria from proteinuria (and vice versa) by a simple linear regression equation, as previously suggested. The RIA has shown a better sensitivity and accuracy in comparison to the dye binding method. Our study suggests that there is not a linear relationship between proteinuria and albuminuria in diabetic patients. Indeed, the ratio between the total proteinuria, as measured with the dye method, and the albuminuria, as measured by a specific and sensitive RIA, varies greatly in diabetic patients with or without glomerular nephropathy. While the dye binding method appears the best procedure for the assay of total microproteinuria, since it is precise, cheap and feasible, the RIA, due to its high sensitivity and specificity, is more suitable for early and accurate detection of microalbuminuria, as well for the close follow-up of subjects at risk of developing overt diabetic nephropathy.