Estimation of Intradialytic Blood Volume Reduction Using Hemoglobin Changes: A Prospective Validation Study of a...

Background/Objectives: Accurate assessment of intradialytic blood volume (BV) changes is important for optimizing fluid management in hemodialysis, but continuous BV monitoring is not universally available. Hemoglobin changes reflect hemoconcentration and may provide a simple surrogate for estimating BV reduction. We prospectively evaluated a hemoglobin-based method for estimating intradialytic BV reduction compared with machine-based BV monitoring. Methods: In this prospective single-center observational study, 187 hemodialysis sessions with complete paired measurements were analyzed. Formula-based BV reduction was calculated from pre- and post-dialysis hemoglobin values and compared with machine-measured BV reduction. Agreement was assessed using Pearson correlation, predefined absolute-difference thresholds, and Bland-Altman analysis. Exploratory receiver operating characteristic analyses evaluated the ability of formula-based estimates to identify sessions with larger machine-measured BV reductions. Results: Formula-based and machine-measured BV reduction demonstrated a moderate-to-strong correlation (r = 0.645). The predefined pragmatic agreement criterion of ≥70% of measurements within ±5% was met, with 77.5% of measurements within this range. Bland-Altman analysis demonstrated a small mean bias of -1.5%, with 95% limits of agreement from -12.4% to 9.3%. Exploratory classification performance was favorable across machine-defined BV reduction thresholds, with area under curve (AUC) values ranging from 0.84 to 0.87. At the ≥8% threshold, sensitivity was 72%, specificity 85%, positive predictive value 83%, and negative predictive value 74%. Linear regression showed that 42% of variability in machine-measured BV reduction was explained by the formula-based estimate. Conclusions: A hemoglobin-based approach provides a simple approximation of intradialytic BV reduction. Although not interchangeable with continuous monitoring, it may support post-session assessment and longitudinal evaluation of intradialytic hemodynamic tolerance.