Objective: To evaluate the consistency between total vitamin B12 and holotranscobalamin (holoTC) measurement results by analyzing holoTC levels in patients with total vitamin B12 deficiency.

Material and Methods: HoloTC level was analyzed by chemiluminescent microparticle immunoassay method in randomly selected serum samples from patient samples (n=98) whose serum total vitamin B12 level was low. <47 pg/mL (<35 pmol/L) was defined as the cut-off value for active B12 deficiency. Those with holoTC levels below this value were considered consistent with the total B12 levels, and those above this value were considered as inconsistent.

Results: The mean ± standard deviation for serum total vitamin B12 and a holoTC was 147 ± 29 and 39.29 ± 18.60 pg/mL, respectively. A weak and significant correlation was observed between holoTC and total vitamin B12 levels (r =0.249, p=0.013). The regression equation was determined as holoTC = 15.91 + 0.158 total vitamin B12. HoloTC level was sufficient in 26% of 98 patients with low total vitamin B12 levels.

Conclusion: The use of holoTC instead of total vitamin B12 according to the patient's clinic data or the inclusion of holoTC as a reflex test in the routine may be useful in the diagnosis and follow-up of patients.