A summary of the different diagnostic methods for vitamin B12 deficiency in end-stage kidney disease patients, their utility, and cut-off criteria.

Table 1: A summary of the different diagnostic methods for vitamin B12 deficiency in end-stage kidney disease patients, their utility, and cut-off criteria.

Diagnostic Method	Use in ESKD	Cut-off Criteria for Deficiency
Serum Vitamin B12 Level	Often used as a first-line screening test Limited use due to false normal and inactive analogues (functional deficiency)	< 200 pg/ml Levels < 100 pg/ml have 90% specificity for identifying clinically evident deficiency
Methylmalonic Acid	More sensitive in ESKD; elevated due to kidney dysfunction	> 0.4 µmol/L
Homocysteine	Elevated in ESKD; affected by B12 and folate status	> 15 µmol/L
Holotranscobalamin (Active-B12)	Promising but requires more research for ESKD specific cut-offs	< 50 µmol/L
Neutrophil Hypersegmentation	Rarely used; not sensitive for mild deficiency	Presence of > 5% neutrophils with ≥ 5 lobes
Macrocytosis (MCV)	May be present but not specific; affected by other factors in ESKD	MCV > 100 fL