All about B12 Testing
B12 is usually measured at total B12 (NHS) and is not necessarily a good guide to usable B12 levels. In blood it is bound either to haptocorrin (inactive) or transcobalamin (active). If we have a measure for active, then that gives us a better picture of B12 available for utilisation, although still might not be the whole story of course, because it still doesn’t tell us about clinical need or actual utilisation, as is the case with any blood test. What do the enzymes do with it when they use it as a cofactor? This is where SNPs (giving us a picture of potential reduced or upregulated enzymatic function) or biomarkers that are a reflection of B12 activity (homocysteine/MMA etc), can help.
In terms of levels, we'll use OptimalDX (in UK, FunctionalDX), as a reference point, although there is some variation in opinions on ranges as usual. There is no 'one truth' as levels are agreed upon by various scientific bodies by consensus. OptimaDx range for total is 450-800 pg/mL (advise investigation if below 542 pg/mL (400 pmol/L) or above 881 pg/mL (650 pmol/L). As Active is roughly 10 - 30% of total, someone in “normal,” range might actually be B12 deficient. OptimalDx benchmarks active B12 at 54-188 pmol/L, suggesting investigation if below 70 (see below).
So, low total B12 is likely to be an issue, whatever. If we see that (and of course in context of SNPs), we’ll want to do something. BUT..
‘Normal' total B12 may still not be sufficient. UK NHS considers above 250 pg/mL to be normal (BUT OptimalDx value is at least 542 pg/mL) And of course we would want to consider if it’s sufficient for the person’s needs, available, and being utilised. So if between approximately 25 and 500, we’d want to look at active B12 if we can, and/or MMA/homocysteine (functional biomarkers that indicate if being used), symptoms (fatigue, neurological), and SNPs (potential down regulation of genes using B12). In other words - NHS ’normal’ - look at the number and investigate further.
Even if we are at or above our optimal levels, there might be too little active available or, if there is, being utilised, so we could we should always consider SNPs, checking active levels if we don’t know, and/or MMA/homocysteine as biomarkers. Again, blood tests only tell us levels of availability NOT need/usage.