Active B12 (holoTC)

The Architect Active- B12 assay is a two-step immunoassay for the quantitative determination of holotranscobalamin in human serum using chemiluminescent microparticle immunoassay (CMIA) technology
Clinical details: 
The current convention is to estimate the abundance of vitamin B12 using total serum vitamin B12 as the first-line screen for deficiency. However this test has a low sensitivity. Up to 45% of vitamin B12-deficient/insufficient subjects may be overlooked if only serum B12 is used as a screening test. Active B12 (holotranscobalamin - holoTC) is the metabolically active portion of B12. Emerging evidence indicates that a low level of Active B12 is a more reliable marker of impaired vitamin B12 status than a low level of serum vitamin B12. Moreover unlike serum B12, Active B12 is believed to be stable in pregnancy. Several studies support Active B12 measurement as a first-line diagnostic test, and suggest that Active B12 may be the earliest marker for B12 depletion.
Reference range: 

>70*; * between 25-70 referred for MMA

Synonyms or keywords: 
holoTC, holotranscobalamin, holoTC II, TC-B12/vitamin B12 deficiency, pernicious anaemia
Sample type and Volume required: 
Minimum 0.5mL
Call in advance: 
Turnaround time: 
Samples processed daily between Mon-Friday (9am-5pm).
Storage and transport: 
Separated serum can be sent by first class post.
Time limit for extra tests: 
MMA analysed within 5 working days
Nutristasis Unit at St Thomas'
020 7188 6815 / 89543
St Thomas' Hospital
North Wing - 4th Floor
Westminster Bridge Road
London SE1 7EH

Laboratory opening times
Monday - Friday 09.00 - 17.00
For clinical advice or interpretation of results, please contact the laboratory in the first instance.

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Last updated: 25/01/2019