Vitamin B12 Dialyzability in Hemodialysis
Vitamin B12 (cobalamin) is not significantly removed by dialysis, and most dialysis patients maintain normal cobalamin levels without supplementation.1
Evidence on Vitamin B12 and Dialysis
The KDOQI Clinical Practice Guidelines for Nutrition in Children with CKD clearly state that most adult and pediatric patients with chronic kidney disease (CKD) and those receiving dialysis have normal cobalamin levels, regardless of whether they receive supplements1. This indicates that vitamin B12 is not significantly dialyzable.
Key points regarding vitamin B12 in dialysis patients:
- Dietary intake of vitamin B12 typically meets or exceeds the Dietary Reference Intake (DRI) in dialysis patients1
- Unlike water-soluble vitamins such as vitamin C and pyridoxine (B6), which show decreased levels in dialysis patients due to dialysis losses, vitamin B12 levels remain normal1
- Serum vitamin B12 levels can be reliably determined using radioassay methods1
Contrasting Vitamin B12 with Other Vitamins
It's important to understand how vitamin B12 differs from other vitamins in dialysis patients:
- Vitamin B6 (Pyridoxine): Low blood levels are documented in hemodialysis (HD) and continuous peritoneal dialysis (CPD) patients, with dialysis removal contributing to deficiency1
- Vitamin C (Ascorbic acid): Decreased levels are reported in patients with CKD and those on dialysis, with documented dialysis losses1
- Vitamin A (Retinol): Not removed by dialysis and often accumulates in patients with CKD, leading to elevated serum levels1
Clinical Implications
While vitamin B12 is not significantly dialyzable, there are still important clinical considerations:
- Some studies have shown lower serum vitamin B12 levels in hemodialysis patients compared to non-dialyzed CKD patients2, but this is not due to dialytic removal
- Extended hours hemodialysis (>15 hours/week) does not significantly affect vitamin B12 levels compared to conventional hemodialysis3
- Excessive supplementation of vitamin B12 in dialysis patients can lead to hypervitaminosis B12 with very high serum levels that persist for years after discontinuation4
Vitamin B12 as a Middle Molecule Marker
Interestingly, vitamin B12 has been used as a marker for middle molecule clearance in dialysis research:
- Vitamin B12 clearance (Kd-B12) is sometimes used to compute a middle molecule-based dialysis index5
- This use is for research purposes to assess dialyzer performance, not because vitamin B12 deficiency is a concern in dialysis patients
Monitoring and Management
Based on the evidence:
- Routine supplementation of vitamin B12 is generally not necessary for most dialysis patients1
- Monitoring of vitamin B12 levels may be warranted in patients with unexplained anemia2, 6
- If deficiency is identified, oral supplementation at 1500-2000 mcg daily is effective7
Pitfalls to Avoid
- Don't assume vitamin B12 deficiency in dialysis patients with anemia without checking levels
- Avoid unnecessary supplementation of vitamin B12 in dialysis patients, as hypervitaminosis B12 can occur4
- Don't confuse vitamin B12's use as a middle molecule marker in dialysis research with clinical need for supplementation
In summary, vitamin B12 is not significantly removed during dialysis, and most dialysis patients maintain adequate levels without supplementation. This contrasts with other water-soluble vitamins like vitamin C and B6, which are more readily dialyzed and may require supplementation.