Low serum vitamin B-12 levels in chronic high-flux haemodialysis patients

The occurrence of vitamin B-12 (B-12) deficiency in chronic haemodialysis patients and the need for its supplementation in these patients are still matters of debate. We measured serial predialysis serum B-12 levels, at 3- to 6-month intervals, in 67 unselected patients on our high-flux haemodialysis programme. Over a 12-month period, there was a significant fall in serum B-12 from 497 +/- 200 (SD) to 391 +/- 131 ng/l (p < 0.001). 22 patients developed subnormal serum B-12 levels and were commenced on hydroxocobalamin supplements. We were unable to demonstrate B-12 clearance during dialysis using blood side studies. Measurement of B-12 in the dialysate showed that 0-4.5 mu g B-12 was cleared per dialysis. Using these B-12 measurements, in vivo B-12 clearance was estimated at 9.1 ml/min. Dietary studies on 24 unselected patients showed borderline or low B-12 intake in 4 patients. Absorption studies by whole-body counting on 6 patients using Co-57 and Co-58 showed normal B-12 absorption. The same radioisotope studies demonstrated no B-12 adsorption to the dialyser membrane. This study demonstrates that low serum B-12 levels occur in high-flux haemodialysis patients and that losses during dialysis and dietary deficiency may be contributing factors.