Multiple immunoassay interference in a patient with falsely elevated calcitonin

Area of Science:

• Clinical Chemistry
• Endocrinology
• Immunology

Background:

• Calcitonin (CT) is a key marker for medullary thyroid carcinoma (MTC).
• Immunometric assays are widely used for CT measurement.
• Heterophile antibodies (HAbs) are known to interfere with immunoassays.

Observation:

• A patient presented with markedly elevated CT levels inconsistent with clinical findings.
• Thyroglobulin (Tg) and Adrenocorticotropic hormone (ACTH) also showed inaccurate elevations.
• Laboratory investigations revealed macro-aggregates and non-linear dilution, suggesting interference.

Findings:

• Polyethylene glycol precipitation significantly reduced CT, Tg, and ACTH levels.
• Pre-treatment with a heterophilic blocking tube normalized CT levels, confirming HAb interference.
• The presence of HAbs led to falsely high CT, Tg, and ACTH measurements.

Implications:

• Immunoassay interference must be considered in cases of discordant laboratory results and clinical presentation.
• Recognizing HAb interference can prevent unnecessary diagnostic procedures and patient anxiety.
• Implementing specific blocking strategies can improve assay accuracy and patient management.