Influence of the cyclic variation of hydration status on hemoglobin levels in hemodialysis patients.

Background: Maintenance hemodialysis (HD) patients were studied to assess the effect on hemoglobin (Hb) concentration induced by the cyclic variation in hydration status.

Methods: Forty-nine HD patients were examined in three consecutive HD sessions in a 1-week treatment period. In a subgroup of 23 patients, Hb levels also were investigated during the long interdialytic interval.

Results: Hb levels at the end of the long interdialytic interval were significantly lower by 0.5 to 0.6 g/dL (5 to 6 g/L) than those at the end of short intervals. Among all pre-HD and post-HD Hb values, levels measured at the end of short intervals were closest to the mean Hb value of the week, derived from calculation of the area under the curve (12.0 +/- 0.2 g/dL [120 +/- 2 g/L]). Intradialytic Hb increments were different in the three sessions (+1.6 +/- 0.1 g/dL [+16 +/- 1 g/L] after the long interval, +1.1 +/- 0.1 g/dL [+11 +/- 1 g/L] and +1.1 +/- 0.1 g/dL [+11 +/- 1 g/L] after short intervals [P < 0.001] and proportionate to weight loss [-3.4 +/- 0.1, -2.7 +/- 0.1, and -2.6 +/- 0.1 kg, respectively; P < 0.001]). Hb level increment and weight loss correlated directly (r = 0.527; P < 0.0001); each 1 L of ultrafiltration (UF) led to an increase in Hb level of approximately 0.4 g/dL (4 g/L). Plasma refilling accounted for an approximately 45% decrement in the intradialytic increase in Hb level 2 hours post-HD.

Conclusion: This study suggests that: (1) the end of the short interdialytic period is the most appropriate timing for anemia assessment, and (2) the remarkable hemodiluting effect of post-HD plasma refilling protects against excessive increments in Hb levels induced by UF.