Measurement of glomerular basement membrane thickness and its application to the diagnosis of thin-membrane nephropathy.

Morphometry is a valuable diagnostic aid when the glomerular basement membrane is suspected of being abnormally thin. Determination of overall width by the harmonic mean method has been described in detail. Results were given of measurements in 20 control subjects with histologically normal basement membranes and 41 allograft kidneys. Mean +/- 1.5 SDs of a series was found to be the most useful empiric guide to basement membrane widths. It was confirmed that the membrane was thinner in females than in males. The lower end of the respective mean +/- 1.5 SDs range overlapped with thicknesses that occurred in "thin-membrane nephropathy" in women but not in men, although the threshold width below which hematuria was liable to occur was similar, at approximately 340 nm, in both sexes. It is suggested that the higher incidence of symptomatic thin-membrane nephropathy in females is related to their normally thinner glomerular basement membranes, in the context of the common threshold level. Other histologic findings, and the clinical picture, remain relevant to the diagnosis of thin-membrane diseases.