Journal List > Korean J Lab Med > v.30(2) > 1011627

Woo, Kim, Park, Park, and Han: Relationship between the Levels of Holotranscobalamin and Vitamin B12

Abstract

To date, the determination of serum vitamin B12 levels has been the most common laboratory test for the assessment of vitamin B12 status; however, the diagnostic accuracy of this test is low. To obtain a more sensitive marker, a new test to measure holotranscobalamin (holoTC) levels has been introduced. In this study, we assessed 45 patients for whom a vitamin B12 test had been requested and 139 anemic patients. We investigated the associations between the levels of homocysteine (Hcy) and those of holoTC, serum vitamin B12, and folate and assessed the diagnostic value of holoTC levels as a marker for vitamin B12 deficiency. We also determined the precision of the AxSYM holoTC assay by calculating the coefficient of variance (CV). The within-run and between-run precision values were excellent, as all CV values were less than 3.5%. The holoTC levels were low (<35 pmol/L) in 7 samples, and 6 of these samples had normal total serum vitamin B12 levels. In 2 of these samples, high Hcy levels (>12 mmol/L) indicated vitamin B12 deficiency. Thus, the holoTC levels were more sensitive than the serum vitamin B12 levels for indicating vitamin B12 status. If the serum vitamin B12 level is 151-300 pmol/L, the levels of holoTC alone or in combination with serum vitamin B12 levels are likely to be more useful markers than serum vitamin B12 levels alone.

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Table 1.
Demographic data and laboratory results of the 184 patients∗
Variables Patients (N=184)
Sex (female/male) 90/94
Age 61.5 (22-83)
Results of laboratory tests  
Vitamin B12 (pmol/L) 564.7 (115.0-1,475.0)
HoloTC (pmol/L) 22.0-128.0
Hcy (mmol/L) 9.2 (3.0-50.0)
Folate (mg/L) 6.4 (0.8-48.0)

Data are presented as median (range) unless otherwise noted;

Data are presented as ranges because samples with high levels of holoTC (>128.0 pmol/L) were not diluted.

Abbreviations: holoTC, holotranscobalamin; Hcy, homocysteine.

Table 2.
Results of the precision analysis for the AxSYM holoTC assay, which was performed using low and high controls
Material Within-run Between-run Between-day Total
SD CV (%) SD CV (%) SD CV (%) SD CV (%)
Low 0.5 2.9 0.5 2.5 0.7 3.8 1.0 5.5
(21.0 pmol/L)                
High 1.4 3.3 0.4 1.1 2.4 5.7 2.9 6.7
(48.0 pmol/L)                

Abbreviations: holoTC, holotranscobalamin.

Table 3.
Classification of patients (N=184) according to the holo-TC levels and total serum vitamin B12 ranges (P<0.0001)
Total serum vitamin B12 (pmol/L) HoloTC<35 pmol/L HoloTC≥35 pmol/L
100-150 1 0
151-300 4 20
>301 2 157

Abbreviations: holoTC, holotranscobalamin.

Table 4.
Number of patients (N=55) with hyperhomocysteinemia (>12 mmol/L), which was determined to the levels of holoTC and folate
  HoloTC<35.0 pmol/L HoloTC>35.0 pmol/L Total
Folate < 3.0 mg/L 0 10 10
Folate > 3.0 mg/L 2 43 45
Total 2 53 55

Abbreviations: holoTC, holotranscobalamin.

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