Comparison of methodologies to characterize haemoglobin variability in the US Medicare haemodialysis population.

Anaemia is a common complication of renal failure [1]; its appropriate management is an important aspect of dialysis patient care [2]. Due to developments in anaemia management over the past 20 years, average haemoglobin levels have risen steadily and transfusion needs declined [1]. The concern about what constitutes appropriate anaemia management has increased due to results from clinical trials [3–5] and increasing costs of treatment [1]. Considerable month-to-month haemoglobin level change has been demonstrated [1,6–8] and two recent studies, using different methods to characterize haemoglobin variability, came to different conclusions regarding the association between haemoglobin variability and mortality [9,10]. Though many studies have analysed haemoglobin level distributions within dialysis patient populations (interpatient variability) [8,11–13], and some have used a measure of individual-level haemoglobin variability over time (intra-patient variability) as an outcome [14,15], few have focused on describing the extent and nature of intrapatient variability [6,7,9,10,16]. Yang et al. compared residual standard deviation and absolute haemoglobin change methodologies [10], and Gilbertson et al. compared two methodologies based on fluctuations across thresholds [17]. Whether haemoglobin variability affects outcomes independently of underlying patient morbidity and treatment remains unresolved; additional research addressing this topic is likely. Understanding the different ways to characterize haemoglobin variability will help evaluate results of these studies.