Serum or plasma: Serum or plasma vitamin B12 has been measured using commercially available competitive protein binding immunoassays (CPBA). Alternatively, a microbiological assay using L. delbruekiisubsp. lactisATCCTM4797 or 7830 can be used for B12 analysis.
Human milk: In the last 10 years, two methods have been described to accurately analyse human milk vitamin B12 by modifying existing CPBAs to remove interfering amounts of haptocorrin from the milk sample.
Functional B12 assessment
Plasma or urine: methylmalonic acid using mass spectrometry reflects the adequacy of B12 for methylmalonyl CoA mutase function.
Neurological assessment: an alternative biomarker of vitamin B12 status is to make a neurological assessment, including nerve conduction velocity, vibratory sensation, abnormal gait, peripheral neuropathy and MRI which detects loss of white matter in the spinal cord and brain.
Published methods for vitamin B12 assay are available in the following references. Links are provided, where available.
CHEMILUMINESCENCE IMMUNOASSAY FOR B12 IN SERUM OR PLASMA (7, 8)
Pirkle J. Laboratory Procedure Manual: Vitamin B12 (serum) Roche E-170 Vitamin B12 “ECLIA”. In: Nutritional Biomarkers Branch DoLS, National Center for Environmental Health, ed. Atlanta, GA: Centers for Disease Control and Prevention. (7)
For the US NHANES Laboratory Procedure Manual, see this page.
Roche. Elecsys Assays – Updated Method Sheets, Vitamin B12. Mannheim, Germany: Roche, 2013. (8)
MICROBIOLOGICAL ASSAY FOR B12 IN SERUM OR PLASMA (9)
Diagnostics B. Difco & BBL Manual: Manual of Microbiological Culture Media. Sparks, MD: Becton, Dickinson and Company, 2009. (9)
MONOCLONAL ANTIBODY ASSAY FOR SERUM HOLOTRANSCOBALAMIN (10)
Axis-Shield. AxSYM Active-B12 (holotranscobalamin). Abbott Park, IL: Abbott Laboratories Inc., 2007. (10)
LC-MS/MS OR GC-MS/MS FOR SERUM (PREFERRED), RBC, OR URINE METHYLMALONIC ACID (11-13)
Pedersen TL, Keyes WR, Shahab-Ferdows S, Allen LH, Newman JW. Methylmalonic acid quantification in low serum volumes by UPLC–MS/MS. J Chromatogr B 2011;879:1502-6. (11)
Schroder TH, Quay TA, Lamers Y. Methylmalonic acid quantified in dried blood spots provides a precise, valid, and stable measure of functional vitamin B-12 status in healthy women. J Nutr 2014;144:1658-63. (12)
Magera MJ, Helgeson JK, Matern D, Rinaldo P. Methylmalonic acid measured in plasma and urine by stable-isotope dilution and electrospray tandem mass spectrometry. Clin Chem 2000;46:1804-10. (13)
HPLC WITH FLUORESCENCE DETECTION FOR PLASMA HOMOCYSTEINE (14)
Gilfix BM, Blank DW, Rosenblatt DS. Novel reductant for determination of total plasma homocysteine. Clin Chem 1997;43:687-8. (14)
COMPETITIVE ENZYME IMMUNOASSAY FOR B12 IN HUMAN MILK (15, 16)
Lildballe DL, Hardlei TF, Allen LH, Nexo E. High concentrations of haptocorrin interfere with routine measurement of cobalamins in human serum and milk. A problem and its solution. Clin Chem Lab Med 2009;47:182-7. (15)
Hampel D, Shahab-Ferdows S, Domek JM, Siddiqua T, Raqib R, Allen LH. Competitive chemiluminescent enzyme immunoassay for vitamin B12 analysis in human milk. Food Chem 2014;153:60-5. (16)