Alpha-1-microglobulin: an indicator protein for renal tubular function.

A comparison of urinary alpha 1-microglobulin concentrations to the behaviour of other indicators of renal tubular disorders, beta 2-microglobulin, retinol-binding protein and N-acetyl-beta-D-glucosaminidase (NAG) has been made. In acute tubular disorders the concentrations of urinary beta 2M and RBP are highly correlated (r = 0.89) but this is less marked for alpha 1M and beta 2M (r = 0.55) and alpha 1M and RBP r = 0.48. NAG tends to run a parallel course to alpha 1M concentrations but lags behind the recovery of low molecular weight protein reabsorption following injury of the tubular cells. The concentrations of alpha 1M, and in particular its stability at low pH suggest that this protein may be useful in screening for tubular abnormalities and detecting chronic asymptomatic renal tubular dysfunction. Urinary alpha 1M greater than 15 mg/g creatinine is strongly suspicious of a proximal tubular dysfunction. The distinction between pure tubular proteinuria and mixed glomerular and tubular proteinuria requires further analysis.