"Macro transcobalamin causing raised vitamin B12: Case-based laboratory investigation"

Area of Science:

• Clinical Chemistry
• Hematology
• Endocrinology

Background:

• Plasma vitamin B12 (B12) measurement is crucial for diagnosing B12 deficiency.
• Elevated B12 levels are an infrequent but significant finding requiring investigation.

Observation:

• A patient presented with unexpectedly high plasma B12 levels.
• Initial assays suggested a macromolecule involving haptocorrin-bound B12.

Findings:

• Further analysis revealed normal haptocorrin but significantly increased total and holo-transcobalamin (holo-TC).
• These findings indicate the presence of macro-transcobalamin (macro-holo-TC).

Implications:

• Assay variability complicates the identification of B12-binding macromolecules.
• Macro-holo-TC should be considered in cases of unexplained elevated plasma B12.