What is the lower limit for vitamin B12 values?
There is no single universal lower limit for vitamin B12: it differs by measuring device, ethnicity, and life stage. Always have your value assessed in the context of the lab that measured it and your own situation.
The 'lower limit' for vitamin B12 is not a fixed number: it depends on which measuring device the laboratory uses. In a study of 300 healthy adults, the lower limit on the Roche platform was 190 ng/mL, on the Siemens platform 181 ng/mL, and on the Beckman DXi platform only 110 ng/mL. The same person can therefore be assessed as 'normal' at one lab and as abnormal at another.
Ethnicity and age also play a role. An analysis of more than 72,000 individuals showed that the lower limit for Black adults (166 pmol/L) is notably higher than for White or Asian adults (134 pmol/L). Children under 1 year of age have different limits again. A single universal lower limit therefore does not apply to everyone.
For pregnant women, even lower limits apply: a value below 89.9 pmol/L in the first trimester, or below 84.0 pmol/L in the second trimester, may indicate a deficiency. These pregnancy-specific limits have not yet been broadly validated.
Important to know: a value above the commonly used lower limit does not rule out a functional B12 deficiency. In older people, metabolism can already be disrupted while serum B12 still appears 'normal'. Additional markers, such as homocysteine and methylmalonic acid (two substances that accumulate when B12 is not functioning properly), can then help identify a deficiency. If you have doubts about your values, discuss them with your doctor, including the type of device the lab used.
Three controlled claims from two studies (PMID 37669635, 36261053, 31085739) and one older clinical study (PMID 9571392). The platform comparison involved 300 healthy adults; the ethnicity study was retrospective (n=72,091). Units in the source vary (ng/mL and pmol/L); both are reported as supplied.