Nephrol Dial Transplant (2003) 18: 2082-2087
© 2003 European Renal Association-European Dialysis and Transplant Association
Original Article
Prediction of time-averaged concentration of haemoglobin in haemodialysis patients
1Division of Nephrology, Department of Internal Medicine, 2Institute for Medical Informatics, Statistics and Documentation, 3Department of Physiology, University of Graz, Graz and 4Medical Devices Consultant, Köstenberg, Austria
Correspondence and offprint requests to: Peter Krisper, MD, Division of Nephrology, Department of Internal Medicine, University of Graz, Auenbruggerplatz 27, A-8036 Graz, Austria. Email: peter.krisper{at}uni-graz.at
Background. Haemoglobin (Hb) concentration is not stable in most haemodialysis patients due to ultrafiltration-induced haemoconcentration. Pre-dialysis Hb concentrations might therefore significantly deviate from the time-averaged concentration (Hb-tac) which is more likely to represent the patients ‘true’ Hb. This study was performed to quantify these differences in our chronic haemodialysis population and to develop a formula for prediction of Hb-tac.
Methods. In 55 stable patients, serial blood samples were taken over a period of 2 weeks before and immediately after each haemodialysis as well as 30 min post-haemodialysis to account for post-dialytic fluid rebound. Hb-tac was calculated for every patient from the area under the time-dependent Hb curve. We compared the differences between Hb-tac and pre-dialysis Hb (Hb-pre) and various prediction formulae for Hb-tac generated by multiple linear regression analysis which included Hb-pre and post-dialysis Hb (Hb-post) and/or ultrafiltration rate (UFR).
Results. Mean Hb-pre after the long dialysis interval was significantly lower than after the short interval (11.47 vs 11.85 g/dl, P < 0.0001), both underestimating mean Hb-tac (11.97 g/dl). More interestingly, Hb-pre after the long interval deviated >0.5 g/dl from Hb-tac in 50% of measurements. After the short interval, 20% still lay outside this tolerance range. The best formula to predict Hb-tac was Hb-pre x 0.5 + Hb-post x 0.38 + 1.28 (6% outside ± 0.5 g/dl). Hb-pre +(Hb-post – Hb-pre)/3 may be used for quick estimation of Hb-tac.
Conclusions. Hb-tac can be predicted from pre- and post-dialysis blood samples after the short interval, using a simple new formula. Because Hb-tac more reliably reflects a ‘true’ Hb level of haemodialysis patients, it represents a potentially useful tool for future scientific and clinical work.
Keywords: haemodialysis; haemoglobin; post-dialysis; prediction; target; time averaged