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False serum calcitonin high levels using a non-competitive two-site IRMA
M Tommasi1, A Brocchi, A Cappellini
1Nuclear Medicine Unit, Department of Clinical Physiopathology, University of Florence, Italy. m.tommasi@dfc.unifi.it
Journal of Endocrinological Investigation
|June 16, 2001
Summary
Heterophile antibodies can cause false positives in calcitonin (CT) immunoassays for medullary thyroid carcinoma (MTC). Even standard blocking methods may not fully prevent this interference, requiring critical interpretation of high CT levels.
Area of Science:
- Clinical Chemistry
- Immunodiagnostics
- Endocrinology
Background:
- Dual site antibody immunoassays are standard for quantifying serum calcitonin (CT) in medullary thyroid carcinoma (MTC) diagnosis.
- Heterophile antibodies are known to interfere with these assays, leading to inaccurate results.
Observation:
- A case study of a 73-year-old man with multinodular goiter presented with high basal CT levels.
- Fine needle aspiration (FNA) for MTC was negative, and a pentagastrin (Pg) stimulation test showed only a mild CT increase.
- Addition of a heterophilic blocking tube (HBT) reduced CT levels by over 80%, indicating significant interference.
Findings:
- The high serum CT levels were attributed to interference from human heterophilic antibodies.
- Standard assay reagents, including F(ab')2 fragments, were insufficient to completely eliminate this interference.
- This represents a novel cause of calcitonin false positivity in immunoassays.
Implications:
- Clinicians should critically interpret elevated serum CT levels, especially when accompanied by a mild increase during Pg stimulation.
- The presence of heterophilic antibodies should be considered as a potential cause of false-positive CT results.
- Assay validation and reagent optimization may be necessary to mitigate heterophile antibody interference.