Predialysis versus postdialysis hematocrit evaluation during erythropoietin therapy

American guidelines for the management of renal anemia by recombinant human erythropoietin (rHuEPO) recommend collecting a predialysis blood sample to evaluate hemoglobin (Hb) and hematocrit (Hct) levels in hemodialysis patients. Although a predialysis blood sample is appropriate for evaluating when to start rHuEPO treatment, the same sample would not be appropriate for evaluating the target Hb/Hct to be maintained, particularly when normal or near-normal values are pursued. We measured the degree of intradialytic and extradialytic variation of Hb, Hct, and body weight in 68 stable hemodialysis patients on maintenance subcutaneous rHuEPO treatment. Hb and Hct concentrations were determined before and after dialysis. In 16 patients, Hb and Hct concentrations also were assessed 24 hours after the end of dialysis. Predialysis versus postdialysis Hb and Hct concentrations for all patients were 10.5 +/- 1.3 g/dL versus 11.5 +/- 1.3 g/dL (P < 0.0001) and 32 +/- 4% versus 35 +/- 4% (P < 0.0001). The intradialytic percent variation (%Delta) of Hct and body weight were 10 +/- 6% and -6.3 +/- 3.5%. There was a close inverse correlation between %Delta of Hct and Hb and %Delta of body weight (P < 0.0001). In patients with body weight losses 2.5 kg or more per session, the mean %Delta of Hct was 12 +/- 7%. In the 16 patients studied 24 hours after the end of the dialysis session, Hct and Hb values remained significantly higher compared with the predialysis levels (P < 0.001), suggesting a slow reequilibration of the intravascular volume in the first 24 hours after hemodialysis. For these reasons, predialysis samples for monitoring the target Hb and Hct levels in patients treated by rHuEPO should be considered with caution.