Evidence for shrunken pore syndrome in children.

The link between cystatin C and mortality independent of glomerular filtration rate (GFR) in adults has prompted the "Shrunken Pore Syndrome" (SPS) hypothesis, where high serum cystatin C with normal creatinine is explained by smaller glomerular pores, through which creatinine can pass freely, while the larger cystatin C, beta-trace protein (BTP) and pro-inflammatory molecules are retained. This study set out to apply the definition of SPS to children. In 294 children who underwent inulin clearance (Cin) test, serum creatinine, cystatin C and BTP were measured. For all three markers eGFR was calculated using the full age spectrum equations. The ratio eGFR/eGFR was plotted against the error of eGFR(%) (i.e. eGFR-Cin)/Cin*100%). Patients with and without SPS according to different cut-off points of eGFRcys/eGFRcrea and eGFR/Cin (i.e. ≤0.6,0.7,0.8) were compared in terms of eGFR, Cin, error of eGFRx(%) and eGFR/eGFR-ratio. The ratio eGFR/eGFR and error of eGFR(%) were positively correlated. The prevalence of SPS by eGFR/eGFR with a cut-off of 0.6 was 4.8%. Patients with SPS had a more negative error of eGFR(%) and eGFR(%) and higher Cin regardless of the definition. Overestimation of eGFR in patients with SPS was only present when using the eGFR/eGFR rather than the eGFR/Cin definition. Cystatin C and BTP are related independent of creatinine, suggesting glomerular pore size as a common denominator. The prevalence of SPS in children is comparable to adults. For research in SPS, a definition based on eGFR/exogenous clearance study may be useful to study the effect of SPS on creatinine metabolism.