Vitamin B12 testing is performed on all samples.

• If Vitamin B12 is <200 pg/mL: Intrinsic Factor Blocking Antibodies and Antiparietal Cell Antibody (APCA) will be performed at an additional charge.
• If Vitamin B12 is between 200 and 400 pg/mL: Methylmalonic Acid (MMA) will be performed at an additional charge.
• If Methylmalonic Acid (MMA) is >378 nmol/L: Intrinsic Factor Blocking Antibodies and Antiparietal Cell Antibody (APCA) will be performed at an additional charge.

Diagnosis of Vitamin B12 Deficiency. Although often used as the first-line screening test for B12 deficiency, serum B12 measurement used in isolation has a generally poor sensitivity and specificity for detection of B12 deficiency. The National Health and Nutrition Examination Survey (NHANES) opted to use the combination of serum total vitamin B12 and methylmalonic acid (MMA) to monitor B12 status in the United States population.35 In the interest of economy, a number of groups have suggested the use of a sequential selection algorithm for the detection of B12 deficiency. In this approach, a second-line assay (in this case MMA) is performed only when the outcome of the first-line assay (vitamin B12 level) falls in an "equivocal" range.1,7 It has been suggested that borderline B12 levels (200-400 ng/L) should be followed up with measuring MMA levels.1 MMA levels below the upper limit of the reference interval (0-378 nmol/L) are strongly suggestive of normal B12 status.