Comparative Assessment of Pre-Dialysis Fluid Status Using Clinical, Lung, and IVC Ultrasound Methods with Bioimpedance Spectroscopy as Reference Standard in Hemodialysis Patients

Background: Accurate assessment of overhydration in maintenance hemodialysis (MHD) patients remains challenging. The clinical method is widely used but may be unreliable. This study compared the nephrologist’s clinical method, lung ultrasound (LUS), and inferior vena cava (IVC) ultrasound against bioimpedance spectroscopy using a body composition monitor (BCM). Methods: In this single-center cross-sectional study, 98 hypertensive patients receiving twice-weekly MHD were evaluated within 30 min before the second dialysis session of the week. LUS B-lines, IVC diameter index at expiration (IVCDimax), and IVC collapsibility index (IVCCi) were measured. BCM-defined overhydration (>2.5 L) was the reference standard. Results: BCM classified 88/98 (89.8%) patients as overhydrated; among these, LUS, IVC ultrasound, and nephrologist’s clinical classification identified 86, 82, and 65 patients, respectively. LUS B-lines showed the strongest correlation with BCM-defined overhydration (ρ = 0.913) and the highest observed AUC (0.985; exploratory cutoff ≥12 B-lines: sensitivity 97.7%, specificity 90.0%). IVCCi showed a strong inverse correlation (r = −0.830; AUC = 0.940), while IVCDimax showed a moderate correlation (ρ = 0.641; AUC = 0.853). Clinically estimated overhydration showed a strong correlation (r = 0.797) but lower discriminative ability (AUC = 0.679) and a mean bias of −0.887 L. Conclusions: LUS had the highest observed AUC; nephrologist’s clinical classification missed more BCM-defined overhydrated patients than LUS or IVC ultrasound.