Reduction in glomerular pore size is not restricted to pregnant women. Evidence for a new syndrome: ‘Shrunken pore syndrome’

Abstract

The plasma levels of cystatin C, β ₂-microglobulin, beta-trace protein, retinol binding protein (RBP) and creatinine were determined in plasma samples from 111 randomly selected patients with eGFR _{cystatin C} ≤ 60% of eGFR _creatinine and from 55 control patients with 0.9eGFR _creatinine ≤ eGFR _{cystatin C} ≤ 1.1eGFR _creatinine (eGFR _{cystatin C} ≈ eGFR _creatinine). The concentration ratios of cystatin C/creatinine, β ₂-microglobulin/creatinine, beta-trace protein/creatinine and RBP/creatinine were significantly higher in patients with eGFR _{cystatin C} ≤ 60% of eGFR _creatinine than in patients with eGFR _{cystatin C} ≈ eGFR _creatinine. When the patients were divided into three groups with different estimated GFR intervals (≤ 40, 40–60 and ≥ 60 mL/min/1.73m ²) the concentration ratios of cystatin C/creatinine, β ₂-microglobulin/creatinine, and beta-trace protein/creatinine were significantly higher in patients with eGFR _{cystatin C} ≤ 60% of eGFR _creatinine than in patients with eGFR _{cystatin C} ≈ eGFR _creatinine for all GFR intervals. Similar results were obtained when the population without pregnant women was studied as well as the subpopulations of men or of non-pregnant women. Populations of pre-eclamptic women and pregnant women in the third trimester display similar results. Since the production of these four proteins with sizes similar to that of cystatin C is not co-regulated, the most likely explanation for the simultaneous increase of their creatinine-ratios in patients with eGFR _{cystatin C} ≤ 60% of eGFR _creatinine is that their elimination by glomerular filtration is decreased. We suggest that this is due to a reduction in pore diameter of the glomerular membrane and propose the designation ‘Shrunken pore syndrome’ for this pathophysiological state.