Renal biopsy findings in orthostatic proteinuria.

Percutaneous renal biopsy was performed on 15 patients with orthostatic proteinuria and 6 control subjects without proteinuria in order to investigate possible renal alterations. The light-microscopic findings were either normal or showed slight mesangial proliferation in the orthostatic group but were normal in the control subjects, while the immunofluorescence-microscopic study revealed mesangial, capillary or arteriolar deposits of complement C3 and/or immunoglobulins in 10 out of 12 cases with orthostatic proteinuria; complement C3 was seen in only one control subject. The electron-microscopic findings were similar in the two groups, showing slight subepithelial, intramembranous and mesangial alterations. Focal loss of the epithelial foot processes was seen in only one case with orthostatic proteinuria. It is concluded that there are no histological, electron microscopical or immunohistochemical alterations specific for orthostatic proteinuria. A finding of complement in the glomeruli in about half and of immunoglobulin in some of the patients with orthostatic proteinuria is in favour of an association to present or previous glomerulonephritis.