Low serum vitamin B12 levels in chronic high-flux haemodialysis patients.

ABSTRACT

The occurrence of vitamin B12 (B12) deficiency in chronic haemodialysis patients and the need for its supplementation in these patients are still matters of debate. We measured serial predialysis serum B12 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 B12 from 497 +/- 200 (SD) to 391 +/- 131 ng/l (p < 0.001). 22 patients developed subnormal serum B12 levels and were commenced on hydroxocobalamin supplements. We were unable to demonstrate B12 clearance during dialysis using blood side studies. Measurement of B12 in the dialysate showed that 0-4.5 microg B12 was cleared per dialysis. Using these B12 measurements, in vivo B12 clearance was estimated at 9.1 ml/min. Dietary studies on 24 unselected patients showed borderline or low B12 intake in 4 patients. Absorption studies by whole-body counting on 6 patients using 57Co and 58Co showed normal B12 absorption. The same radioisotope studies demonstrated no B12 adsorption to the dialyser membrane. This study demonstrates that low serum B12 levels occur in high-flux haemodialysis patients and that losses during dialysis and dietary deficiency may be contributing factors.