LOW SERUM VITAMIN-B-12 LEVELS IN CHRONIC HIGH-FLUX HEMODIALYSIS-PATIENTS

The occurrence of vitamin B-12 (B-12) deficiency in chronic haemodialy sis patients and the need for its supplementation in these patients ar e still matters of debate. We measured serial predialysis serum B-12 l evels, at 3- to 6-month intervals, in 67 unselected patients on our hi gh-flux haemodialysis programme. Over a 12-month period, there was a s ignificant 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 w ere commenced on hydroxocobalamin supplements. We were unable to demon strate B-12 clearance during dialysis using blood side studies. Measur ement 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 w as 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 nor mal B-12 absorption. The same radioisotope studies demonstrated no B-1 2 adsorption to the dialyser membrane. This study demonstrates that lo w serum B-12 levels occur in high-flux haemodialysis patients and that losses during dialysis and dietary deficiency may be contributing fac tors.