Low Serum Vitamin B ₁₂ Levels in Chronic High-Flux Haemodialysis Patients

Abstract

The occurrence of vitamin B<sub>12</sub> (B<sub>12</sub>) 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<sub>12</sub> 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<sub>12</sub> from 497 ± 200 (SD) to 391 ± 131 ng/l (p < 0.001). 22 patients developed subnormal serum B<sub>12</sub> levels and were commenced on hydroxocobalamin supplements. We were unable to demonstrate B<sub>12</sub> clearance during dialysis using blood side studies. Measurement of B<sub>12</sub> in the dialysate showed that 0-4.5 μg B<sub>12</sub> was cleared per dialysis. Using these B<sub>12</sub> measurements, in vivo B<sub>12</sub> clearance was estimated at 9.1 ml/min. Dietary studies on 24 unselected patients showed borderline or low B<sub>12</sub> intake in 4 patients. Absorption studies by whole-body counting on 6 patients using 57Co and 58Co showed normal B<sub>12</sub> absorption. The same radioisotope studies demonstrated no B<sub>12</sub> adsorption to the dialyser membrane. This study demonstrates that low serum B<sub>12</sub> levels occur in high-flux haemodialysis patients and that losses during dialysis and dietary deficiency may be contributing factors.