BACKGROUND: Bioelectrical impedance (BIA) is a potentially useful method for measuring body water and soft-tissue composition in patients with chronic renal failure. The majority of whole body impedance is derived from the limbs with only a small contribution from the trunk, and thus abnormalities of the limbs could have an exaggerated effect on estimates of total body impedance. METHODS: This study investigated the effect of arteriovenous fistulae in the arm in haemodialysis patients on body composition measurement by whole body BIA. Body composition estimates from measurements on fistula and non-fistula sides of the body were compared and segmental impedance measurements of the arms were also performed. RESULTS: Whole body resistance was markedly lower on the fistula side of the body compared with the nonfistula side at 517.1 (124.3) omega compared with 561.5 (121.2) omega, P < 0.0005. This difference was accounted for by differences in the arm segments. This was attributed to swelling of the fistula arm which had a greater mid-arm circumference at 28.5 (2.1) cm compared with the contralateral side at 27.5 (2.0) cm, P < 0.05. This resulted in greater estimates for total body water from the fistula side at 38.6 (10.0) kg compared with 36.6 (8.6) kg from the non-fistula side, P < 0.05 and fat-free mass at 51.1 (11.8) kg from the fistula side compared with 49.1 (11.2) kg from the non-fistula side, P < 0.005. Estimates of body fat from the fistula side, 13.1 (6.9) kg, were less than the nonfistula side, 15.0 (6.0), P < 0.005. CONCLUSIONS: The presence of arteriovenous fistulae for vascular access in haemodialysis patients may have a significant effect on estimates of body composition by BIA.
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