Part 3: Vitamin B12 insufficiency is common, especially in people 55 or older, vegetarians, or anyone on acid blocking medication. At Metametrix, we look at MMA in urine to evaluate B12 need. Serum B12 has a low predictive value for actual vitamin B12 deficiency. Elevated MMA identifies B12 as insufficient, and as it turns out urine and serum MMA are very closely correlated.
Kwok and colleagues did a study comparing how well serum and urinary measures compare. They choose to look at older vegetarians to ensure they chose a good sample of people who were vitamin B12 insufficient. They found that fasting urinary and serum MMA levels were linearly correlated, with a Pearson's correlation coefficient of 0.94, that’s a great number since 1.0 is a perfect correlation. The cutoff of fasting urinary MMA of 2 microM/mM of creatinine was found to have a high sensitivity and specificity, and a positive predictive value for elevated serum MMA. I compared that to the cut-off we have on the Organix test, we use > 2.3 ug/mg creatinine. So how do the two cut-offs compare? Well, do the math:
Their range is 2 micromolar MMA/1 millimolar createnine, which converts to 2 micromol/1 miilimol (the Liters cancel out) = 2.09 ug/mg creatinine. These are close 2.09 in the study and 2.3 from our population. The level is consistent.
So when you order an Organix Profile for a patient, know that urine is not just a convenient way to do an assessment of vitamin B12, it is a good way.
Next week we'll take a look at Glycine, and why you can’t live, well, without it.