Vitamin B12 biomarker patterns and kidney function in US adults: National Health and Nutrition Examination Survey 2011-2012.

INTRODUCTION Total serum vitamin B12 levels may not align with biomarkers of circulating active vitamin B12 or intracellular vitamin B12-dependent metabolism. We estimated the population prevalence of marker-defined discordance among US adults and examined the influence of kidney function.

Methods

We analyzed National Health and Nutrition Examination Survey 2011-2012 data from 4318 adults with total vitamin B12, holotranscobalamin (holoTC), and methylmalonic acid (MMA) measurements and positive holoTC subsample weights. Low total vitamin B12 was defined as a level less than 200 pg/mL (148 pmol/L), low holoTC as a level less than 35 pmol/L, and elevated MMA as a level greater than 300 nmol/L. Analyses incorporated survey weights, strata, and primary sampling units.

Results

Low total vitamin B12 was present in 1.7% of adults compared with low holoTC in 4.7% of adults and elevated MMA in 6.5% of adults. Overall, 9.7% of adults had low holoTC or elevated MMA. Among these adults, 60.6% had total vitamin B12 levels greater than 300 pg/mL. In a secondary integrated analysis, 2.2% (95% CI, 1.5%-2.9%) had a 3-marker combined vitamin B12 indicator less than -0.5. Methylmalonic acid-based discordance increased with declining estimated glomerular filtration rate.

Discussion

Marker-defined low holoTC or elevated MMA was more common than low total vitamin B12. Methylmalonic acid should be interpreted in the context of kidney function.