The mortality increase in cardiac surgery patients associated with shrunken pore syndrome correlates with the eGFRcystatin C/eGFRcreatinine-ratio

Shrunken pore syndrome (SPS) is a condition in which estimated glomerular filtration rate (eGFR) based upon cystatin C is lower than eGFR based upon creatinine. It has been associated with increased mortality even in the presence of normal GFR in both a cardiac surgical population and a general population. No systematic studies of the variation in eGFR(cystatin C)/eGFR(creatinine)-ratio used for SPS diagnosis have been published. This study aims to evaluate whether early and midterm mortality following elective cardiac surgery varies with the ratio used to identify SPS. Preoperative levels of cystatin C and creatinine were analysed in 4007 patients undergoing elective coronary artery bypass grafting (CABG) and/or surgical aortic valve replacement (sAVR). The eGFR(cystatin C)/eGFR(creatinine)-ratio was calculated based on the equation pairs CKD-EPIcystatin C/CKD-EPIcreatinine and CAPA/LMrev. The overall 1- and 3-year all-cause mortality was 2.9 and 6.8%, respectively. Mean follow-up time was 3.6years. Mortality markedly and progressively increased with a decrease in the eGFR(cystatin C)/eGFR(creatinine)-ratio for both equation pairs. An increase in mortality was noted already when the ratio decreased from 1.0 to 0.90. To facilitate the clinical decisions based upon the SPS-defining eGFR(cystatin C)/eGFR(creatinine)-ratio, we calculated both the ratios defining the highest combined sensitivity and specificity and the ratios producing a high specificity of 95%, finding different cut-off for these scenarios.