Haemoglobin at time of referral prior to dialysis predicts survival: an association of haemoglobin with long-term outcomes

Haemoglobin (Hgb) levels are known to be associated with numerous adverse outcomes in both chronic kidney disease (CKD) and non-CKD patients. This analysis evaluates the association of baseline haemoglobin levels on survival in CKD patients, who are followed by nephrologists, irrespective of glomerular filtration rate (GFR), prior to initiation of renal replacement therapy (RRT) and erythropoietin hormone replacement therapy. Analysis of data from the provincial database (PROMIS, Patient Registration and Outcome Management Information System) in British Columbia, Canada, was undertaken. Records used for the analysis included all CKD patients at first registration: GFR < 60 ml/min/1.73 m(2), not yet on dialysis, starting from May 1998 to October 2002, and who had complete data (defined as age and gender, diabetic status, eGFR and Hgb levels). The primary objective of this study was to determine the association of Hgb and survival controlling for eGFR at first registration value, age, gender and diabetic status. Multivariate Cox proportional hazards analysis with time to death as outcome variable was performed. The cohort included 3028 patients: the mean age was 65 years, 28% were diabetic, and the mean eGFR in the cohort was 21 ml/min/1.73 m(2). The cohort is representative of the BC CKD and dialysis population regarding ethnicity: 64% Caucasian, 32% Asian. Median follow-up was 27 months, 1 year survival was 0.92, 2 year survival was 0.85. Hgb at initial registration is a statistically independent predictor of survival (RR = 0.875 for every 10 g/l, 95% CI: 0.835-0.917, P = 0.0001), after adjusting for age, gender, diabetic status and baseline eGFR. Further analysis, controlling for RRT, demonstrated a similar association between Hgb and survival (RR = 0.853 for every 10 g/l, 95% CI: 0.799-0.910, P = 0.0001), after adjusting for above variables. Substantial variation in Hgb values exists at all GFR levels. These findings underscore the importance of evaluating Hgb at all GFR levels, and the need to study the impact of modification of Hgb at different GFR levels on survival.