Anion gap predicts early mortality after starting hemodialysis in the elderly

Background Serum anion gap (AG) has recently been proven to represent a biomarker for predicting prognosis in patients with end-stage renal disease (ESRD). However, whether change in AG (ΔAG) at the time of starting hemodialysis predicts mortality after starting hemodialysis in elderly patients with ESRD remains unknown. Methods This retrospective cohort investigated the association between ΔAG and mortality after starting hemodialysis in the elderly. The cohort comprised patients ≥ 75 years old who started hemodialysis for ESRD at National Center for Global Health and Medicine between 2010 and 2017 and at Yokosuka Kyosai Hospital between 2007 and 2011. Patients were stratified into three groups (G1-3) based on ΔAG, calculated according to the equation: ΔAG = sodium − (chloride + bicarbonate) − 12. The primary outcome was death within 1 year of starting hemodialysis. Data were analyzed using Cox proportional hazard models with adjustments for baseline characteristics. Results We enrolled 254 patients (59% male). Median ΔAG was 2.6 (G1: > 3, n = 111; G2: 0–3, n = 103; G3: < 0, n = 40). The primary outcome was observed in 43 patients. Hazard ratios (HRs) were significantly higher for G1 and G3 than for G2 (G1: HR 2.47, 95% confidence interval 1.13–5.37; G3: HR 3.86, 95% confidence interval 1.62–9.16). Adjusted HRs (aHRs) were significantly higher for G1 and G3 than for G2 (G1: aHR 3.06, 95% confidence interval 1.23–7.62; G3: aHR 3.12, 95% confidence interval 1.10–8.78). Conclusions A J -curve phenomenon is evident between ΔAG and early mortality after starting hemodialysis in the elderly.