Prediction of time-averaged concentration of haemoglobin in haemodialysis patients.
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.
D000328:Adult; D000368:Aged; D000740:Anemia / Q000175:diagnosis* / Q000209:etiology; D001774:Blood Chemical Analysis; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000175:diagnosis / Q000628:therapy*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011237:Predictive Value of Tests; D011336:Probability; D006435:Renal Dialysis / Q000009:adverse effects* / Q000379:methods; D018570:Risk Assessment; D012494:Sampling Studies; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013997:Time Factors
D006454:Hemoglobins