Markers · Vitamins
A B12 of 350, in range by the lab's numbers. Vitamin B12, read against the rest of you.
What vitamin B12 measures, what it does in the body, why it's tested, and the two ranges it's read against. Everything said about the marker here comes from Merlin's own biomarker catalogue.
What vitamin B12 is
B12 is an essential cofactor for converting homocysteine to methionine (methylation) and for breaking down methylmalonyl-CoA. Low B12 stalls the methylation cycle and shows up as rising homocysteine and methylmalonic acid (MMA) - which is why serum B12 alone can miss functional deficiency, and MMA/homocysteine confirm it.
What it does in the body
As methylcobalamin, B12 is the cofactor for methionine synthase (remethylating homocysteine → methionine → SAMe, the universal methyl donor); as adenosylcobalamin, it is the cofactor for methylmalonyl-CoA mutase in mitochondrial energy metabolism. It is essential for myelin maintenance, red-cell production, and DNA synthesis.
Why it's tested
Used to evaluate macrocytic anemia, peripheral neuropathy or cognitive change, malabsorption (pernicious anemia, post-bariatric, metformin/PPI use, vegan diets), and methylation status. Best interpreted alongside MMA and homocysteine, which rise early in true deficiency.
The two ranges
The reference range reflects population statistics. The target reflects physiology.
- Lab reference range
- 200-900 pg/mL (deficiency < 200; borderline 200-300)
- Functional target
- 545-1100 pg/mL
Those are different numbers, and you deserve to know which one you're looking at. Merlin reads your result against both.
Where this lives
A Field Guide to Depression & Low Mood
The field guide that covers vitamin B12 in depth, whole and public.
In a real read
There's no B12 in the real Cardiovascular read on this site, but the marker it moves is there: homocysteine at 7.7 umol/L, in an endothelial axis the read calls "clean". That's how a marker gets read, beside the ones it changes.
A real Cardiovascular surface from a real anonymized panel: the score, the narrative, the layers underneath. Yours will be built the same way, on your own numbers.
Educational context for your conversations with your licensed healthcare provider, not a diagnosis or a treatment plan. Merlin reads results; it doesn't diagnose.
Bring the panel this number came from. Merlin reads it against everything else you have, every system and every year, then shows you what it means and what's worth finding out next. Start with your first month.