Correlations between renal interstitium and level of serum creatinine. Morphometric investigations of biopsies in perimembranous glomerulonephritis.

Morphometric investigations in 40 patients suffering from perimembranous glomerulonephritis at different stages showed that there is no certain relationship between the severity of glomerular lesions and the serum creatinine level. In 19 cases in stages I-III, with serum creatinine level less than 1.2 mg/100 ml on biopsy, the renal interstitium was less enlarged than in 21 cases in the same stages, but with serum creatinine level higher than 2 mg/100 ml. There is a significant positive correlation between the relative interstitial volume and the level of serum creatinine. The best congruence was demonstrated in the lin/log-plotting indicating that our values correlate best with an exponential function. We therefore conclude that in perimembranous glomerulonephritis, generally considered to be a glomerular disease, functional impairment cannot be explained by the glomerular lesions alone; interstitial changes have also to be taken into account as a cause of renal insufficiency. The following hypothesis is proposed; that the increase in renal interstitium and possible shrinking of collagen fibres may lead to a narrowing of intertubular capillaries. This may result in slowing of glomerular blood flow and may lead to renal insufficiency.