Plasma exchange induces vitamin D deficiency

Background: Plasma exchange is used in the treatment of diseases mediated by pathogenic circulating proteins, or for transplant desensitization. Its non-targeted nature results in the depletion of physiologically important molecules, and it is often complicated by hypocalcaemia. Aim: To determine the effects of plasma exchange on vitamin D binding protein (DBP) and associated vitamin D metabolites. Design: Single-centre prospective cohort study of 11 patients. Methods: DBP and vitamin D metabolites were measured before and immediately after five plasma exchanges, and 7 and 28 days after discontinuation of plasma exchange. Results: Plasma exchange reduced plasma DBP concentration from 196.9 +/- 53.2 to 98.5 +/- 34 mu g/ml (P = 0.0001), 1,25-dihydroxyvitamin D from 103 +/- 52 to 42 +/- 4 pmol/l (P = 0.003) and 25-hydroxyvitamin D from 49.7 +/- 29 to 22 +/- 9.4 nmol/l (P = 0.0017), through their removal in effluent. After 7 days, DBP and 1,25-dihydroxyvitamin D were not significantly different from baseline, but 25-hydroxyvitamin D remained significantly lower after 7 days (26.4 +/- 9.8 nmol/l, P = 0.02) and 28 days (30.8 +/- 15.5 nmol/l, P = 0.048). Corrected calcium decreased from 2.23 +/- 0.11 to 1.98 +/- 0.08 mmol/l (P = 0.0007) immediately after five treatments. Plasma calcium was significantly associated with 1,25-dihydroxyvitamin D (r(2) = 0.79, P < 0.0001). Conclusions: Plasma exchange induced an acute reversible decrease in plasma 1,25-dihydroxyvitamin D, DBP, calcium and a sustained decrease in plasma 25-hydroxyvitamin D.