Physiological and Clinical Implications of Timing of Hemoglobin Measurement in Hemodialysis

Introduction Management of anemia in patients undergoing maintenance hemodialysis is primarily based on predialysis hemoglobin measurements. However, hemoglobin concentrations vary substantially across the hemodialysis cycle because of interdialytic fluid accumulation, ultrafiltration‐induced hemoconcentration, and ongoing plasma refilling. Consequently, hemoglobin values obtained at different time points are not physiologically equivalent and may reflect distinct circulatory states. Methods This narrative review summarizes the physiological determinants of hemoglobin variation during the hemodialysis cycle and examines the clinical implications of different hemoglobin sampling strategies in patients undergoing maintenance hemodialysis. Findings Sampling practices differ across regions: in Japan, hemoglobin is commonly assessed during the first dialysis session of the week, whereas midweek predialysis sampling is frequently used in North America and Europe and is explicitly recommended by the 2025 UK Kidney Association guideline. Pre‐ and postdialysis hemoglobin measurements reflect different physiological conditions and may lead to different interpretations of anemia severity and hemoglobin variability. Discussion Greater attention to the timing and standardization of hemoglobin measurement may improve interpretation of anemia severity and hemoglobin variability and enhance the international comparability of clinical data in patients undergoing maintenance hemodialysis. Consideration of physiologically relevant sampling strategies may contribute to a more accurate assessment of anemia in routine dialysis practice.