Changes in serum osmotic pressure following haemodialysis treatments lead to changes in bioimpedance spectroscopy estimates of lean and adipose tissue.

Haemodialysis (HD) patients are at risk of sarcopenia. Newer bioimpedance devices (BIS) using a three-compartmental body composition model, separate extracellular water overhydration from normo-hydrated lean tissue mass (LTM) and adipose tissue mass (ATM). During HD hydration status changes, along with changes in electrolytes and solutes, and may alter body composition measurements. As such, we measured BIS and serum osmotic pressure (sOP) pre- and post dialysis in 43 patients. There were no significant changes in LTM (39.5±15.1 vs 39.3±15.2 kg) or sOP (33.2±8.3 vs 35.9±9.7 mm Hg). Higher post-dialysis sOP was associated with a greater percentage fall in LTM (r=0.43, P=0.08) and increase in ATM (r=-0.43, P=0.017). Increased sOP post dialysis was associated with a reduction in LTM (r=0.36, P=0.033) and increased ATM (r=-0.44, P=0.013). Changes in sOP with HD are associated with changes in BIS body composition measurements. BIS measurements should preferably be made when patients are least overhydrated.