Necessity of adjusting the blood hemoglobin target owing to interdialytic weight gain in patients on maintenance hemodialysis

To the Editor: Anemia is a common complication in patients on maintenance hemodialysis, and its correction with erythropoiesis-stimulating agents is an established therapy. Current guidelines indicate the target blood hemoglobin levels for administering erythropoiesisstimulating agents but do not specify the hemoglobin measurement conditions, which reportedly affect hemoglobin in maintenance hemodialysis patients. Notably, hemoglobin decreases in case of hemodilution, such as that caused by interdialytic weight gain, and a difference in the gain would generally result in pre-dialysis hemoglobin measured early in the week (early-week-preHb) being lower than that measured midweek (midweekpre-Hb). However, studies examining this hemoglobin difference are scarce and have reported varying results; the difference was only 0.9% in one study but 4.3% in another. Thus, we aimed to examine this difference. This study was performed at a dialysis center in accordance with the Declaration of Helsinki. Pre-dialysis hemoglobin was measured during consecutive earlyweek and midweek maintenance hemodialysis sessions in 12 patients who were undergoing three maintenance hemodialysis sessions per week and were not on the therapy with erythropoiesis-stimulating agents. Comparisons were performed using Student’s paired t-test. Table 1 summarizes the measurements. The mean and median of the early-week-pre-Hb to midweek-pre-Hb ratio were 96.1% and 96.8%, respectively. Therefore, early-week-pre-Hb was lower than midweek-pre-Hb by approximately 4%. In the present analysis, interdialytic weight gain relative to dry weight—the target weight after a dialysis session (IDWG/DW)—was approximately 5.5% and 4.2% in the early-week and midweek sessions, respectively. This increase reduced early-week-pre-Hb by approximately 4% compared with midweek-pre-Hb. Thus, hemoglobin decreased by approximately 3% per additional 1% increase in IDWG/DW. As the daily IDWG/DW is typically 1.5%, the present findings support the previous finding that early-week-pre-Hb was lower than midweekpre-Hb by approximately 4.5%. Interdialytic weight gain is primarily attributed to increased extracellular fluid. As extracellular fluid accounts for approximately one-third of the total body fluid, which in turn accounts for approximately