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 numerousadverse outcomes in both chronic kidney disease (CKD) and non-CKDpatients. This analysis evaluates the association of baseline haemoglobinlevels on survival in CKD patients, who are followed by nephrologists,irrespective of glomerular filtration rate (GFR), prior to initiationof renal replacement therapy (RRT) and erythropoietin hormonereplacement therapy. Analysis of data from the provincial database (PROMIS, PatientRegistration and Outcome Management Information System) in BritishColumbia, Canada, was undertaken. Records used for the analysisincluded all CKD patients at first registration: GFR <60ml/min/1.73 m², not yet on dialysis, starting from May 1998to October 2002, and who had complete data (defined as age andgender, diabetic status, eGFR and Hgb levels). The primary objective of this study was to determine the associationof Hgb and survival controlling for eGFR at first registrationvalue, age, gender and diabetic status. Multivariate Cox proportionalhazards analysis with time to death as outcome variable wasperformed. 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/1.73m². The cohort is representative of the BC CKD and dialysispopulation regarding ethnicity: 64% Caucasian, 32% Asian. Medianfollow-up was 27 months, 1 year survival was 0.92, 2 year survivalwas 0.85. Hgb at initial registration is a statistically independentpredictor 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, controllingfor RRT, demonstrated a similar association between Hgb andsurvival (RR = 0.853 for every 10 g/l, 95% CI: 0.799–0.910,P = 0.0001), after adjusting for above variables. Substantialvariation in Hgb values exists at all GFR levels. These findings underscore the importance of evaluating Hgb atall GFR levels, and the need to study the impact of modificationof Hgb at different GFR levels on survival.