Renal function estimation and one-year mortality in elderly patients with non-ST-segment elevation acute coronary syndromes

Abstract

Chronic renal dysfunction is relatively common in patients hospitalized for acute coronary syndrome (ACS) and is among the most powerful predictors of adverse in-hospital outcomes [ [1] Al Suwaidi J. Reddan D.N. Williams K. et al. Prognostic implications of abnormalities in renal function in patients with acute coronary syndromes. Circulation. 2002; 106: 974-980 Crossref PubMed Scopus (419) Google Scholar ]. Mathematical estimations of glomerular filtration rate (GFR), based on serum creatinine concentration, have emerged as a clinically useful method to more accurately measure renal function. The Cockcroft–Gault (CG) equation has been the traditional method of estimating GFR for drug dosing [ [2] Cockcroft D.W. Gault M.H. Prediction of creatinine clearance from serum creatinine. Nephron. 1976; 16: 31 Crossref PubMed Scopus (12986) Google Scholar ]. More recently, the Modification of Diet in Renal Disease (MDRD) formula and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation have been developed and shown to perform better than the CG equation in terms of precision and accuracy [ [3] Michels W.M. Grootendorst D.C. Verduijn M. Elliott E.G. Dekker F.W. Krediet R.T. Performance of the Cockcroft–Gault, MDRD, and new CKD-EPI formulas in relation to GFR, age, and body size. Clin J Am Soc Nephrol. 2010; 5: 1003-1009 Crossref PubMed Scopus (354) Google Scholar ]. However, neither >formula was specifically developed or validated in patients with heart diseases, especially the elderly and the very elderly [ [2] Cockcroft D.W. Gault M.H. Prediction of creatinine clearance from serum creatinine. Nephron. 1976; 16: 31 Crossref PubMed Scopus (12986) Google Scholar ]. The Italian Elderly ACS study, the first specifically investigating treatment strategies for elderly patients with non ST-elevation ACS (NSTEACS), represents a unique opportunity to investigate this issue. Details of the study design and population have been published [ [4] Savonitto S. Cavallini C. Petronio A.S. et al. Italian Elderly ACS Trial InvestigatorsEarly aggressive versus initially conservative treatment in elderly patients with non-ST-segment elevation acute coronary syndrome: a randomized controlled trial. JACC Cardiovasc Interv. 2012; 5: 906-916 Abstract Full Text Full Text PDF PubMed Scopus (177) Google Scholar ]. Overall 645 patients aged ≥75 years were enrolled in the trial or included in a parallel registry. Signature of an informed consent form was a prerequisite for enrolment. The study protocol conformed to the ethical guidelines of the 1975 Declaration of Helsinki as reflected in a priori approval by the institution's human research committee. Serum creatinine (Cr) was analyzed according to the method used in each local laboratory. The GFR from the CG equation was estimated as: ([{140 − age in years} × body weight in kg] / {72 × Cr in mg/dl}) × 0.85 (female gender); for the MDRD formula as: [186 × (Cr in mg/dl)−1.154] × (age)−0.203 × (0.742 if female) and for the CKD-EPI equation as: 141 × min [(Cr (in mg/dl) / κ, 1)α] × max (Cr / κ, 1)−1.209 × 0.993age × (1.018 if female), where κ is 0.7 for females and 0.9 for males and α is −0.329 for females and −0.411 for males. For comparison with other equations, the predicted creatinine clearance by CG was normalized per 1.73 m2 of body surface area (BSA). We defined normal renal function as estimated GFR >60 ml·min·1.73 m−2, mild to moderate renal dysfunction as estimated GFR <60 and >30 ml·min·1.73 m−2 and severe renal dysfunction as estimated GFR <30 ml·min·1.73 m−2.