Assessment of glomerular charge selectivity in man by differential clearance of isoamylases.

1. Glomerular charge selectivity was assessed using the ratio of the clearance of pancreatic isoamylase to the clearance of the more anionic salivary isoamylase (CPAm/CSAm) in 30 normal subjects, 14 patients with minimal proteinuria and 23 patients with heavy proteinuria due to primary glomerulopathies. Seven patients with minimal change nephropathy were studied in relapse and remission. 2. CPAm/CSAm exceeded 2.0 (range 2.1-6.1) in all normal subjects, indicating that the normal glomerular capillary wall possesses charge selectivity at the molecular size of amylase (molecular mass 56 kDa). 3. CPAm/CSAm was significantly lower in patients with heavy proteinuria than in normal subjects or patients with minimal proteinuria. CPAm/CSAm was low in patients with minimal change nephropathy in relapse and rose into the normal range with steroid-induced remission. 4. These data suggest that heavy proteinuria in primary glomerulopathies is accompanied by loss of glomerular charge selectivity. Remission of minimal change nephropathy is associated with restoration of normal charge selectivity.