[A study of urinary immunoglobulin excretion after forced lordosis]

Changes in the urinary excretion of immunoglobulins (IgG and IgA) before and after forced lordosis were studied in 26 children with orthostatic proteinuria (group OA, where proteinuria disappeared within 120 min after lordosis was referred to as group OAA and where if disappeared after more than 120 min was group OAB) and 9 children with chronic glomerulonephritis in the clinically stable state (group GN). Urinary immunoglobulins were measured by ELISA (enzyme linked immunosorbent assay). In resting urine, the urinary excretion rates (total protein, IgG, and IgA) and the urinary protein ratio (IgG/protein, IgA/protein, and IgA/IgG) did not significantly differ between groups OA and GN. When forced lordosis was carried out, at maximum protein excretion, the urinary IgA/IgG ratio in groups OAA and OAB were significantly decreased (from 198 + 44% to 17.3 + 12.9% and from 147 + 88% to 18.7 + 16.9%, respectively). The ratio of IgA/IgG in groups OAA and OAB was significantly lower than that in group GN (88.9 + 53.9%, p less than 0.01). The urinary IgA/IgG ratio after lordosis in group OA was similar to the serum IgA/IgG ratio. These findings suggest that transient low or non-selective proteinuria after lordosis is a characteristic of orthostatic proteinuria. Analysis of the urine after forced lordosis, especially using the urinary IgA/IgG ratio at maximum protein excretion, may be an useful examination for differentiating OA from other glomerulonephritides.