Are ligand assay methods specific for cobalamin? A survey report

Area of Science:

• Clinical Chemistry
• Analytical Toxicology
• Biochemical Assays

Background:

• Cobalamin (vitamin B-12) is essential for human health.
• Non-physiological cobalamin analogues can interfere with laboratory measurements.
• Accurate vitamin B-12 testing is crucial for diagnosing deficiencies and related disorders.

Purpose of the Study:

• To evaluate the ability of clinical laboratories to accurately measure cobalamin in the presence of cobalamin analogues.
• To quantify the interference of cobinamide, a model analogue, on cobalamin assays.

Main Methods:

• Participants in the College of American Pathologists ligand assay survey received serum samples with added cobalamin and/or cobinamide.
• Results from 919 samples using 13 commercially available methods were analyzed.
• Interference was assessed by measuring apparent increases in cobalamin concentration.

Main Results:

• A mean interference of 26.5 pg/mL (range: 18-42 pg/mL) was observed when 400 pg/mL of cobinamide was added to a sample containing 412 pg/mL of cobalamin.
• The mean recovery of added cobalamin was 104% of the expected value, indicating good accuracy.
• Most commercial methods demonstrated acceptable performance.

Conclusions:

• Clinical laboratories can reliably measure cobalamin (vitamin B-12) using current commercial methods, even with the presence of cobalamin analogues like cobinamide.
• The observed interference is generally low and unlikely to cause significant diagnostic errors.
• Assay validation and quality control are essential for ensuring accurate cobalamin measurements.