Selectivity as a clue to diagnosis of postural proteinuria.

In 14 patients with fixed and reproducible postural proteinuria and 14 patients with histologically proven glomerulonephritis, the selectivity of proteinuria was measured separately in the day and night urine collections. The selectivity of proteinuria in the urine collected in recumbency was lower in patients with glomerulonephritis than in patients with postural proteinuria. All patients with postural proteinuria showed an increment of the selectivity from day to night of at least 13 degrees, whereas the maximum increment in patients with glomerulonephritis was 5 degrees. The changes in selectivity from day to night in patients with postural proteinuria and patients with glomerulonephritis were significantly different and seem to be a useful discriminatory test.