title: Spurious hypercalcitoninemia in patients with nodular thyroid disease induced by heterophilic antibodies.
abstract: BACKGROUND
  Serum calcitonin is the most useful tumor marker for the diagnosis and follow-up of medullary thyroid carcinoma (MTC). Spurious hypercalcitoninemia caused by heterophilic antibody interference (HAI) is rarely found in patients without MTC.
  
  
  METHODS
  We studied 2 patients with hypercalcitoninemia and thyroid nodules, but no evidence of MTC on fine-needle aspiration cytology. We performed calcium stimulation tests, measured serum calcitonin with another calcitonin kit, performed dilution tests, and remeasured serum calcitonin after applying heterophilic blocking tubes.
  
  
  RESULTS
  In a 31-year-old woman with no response to the calcium stimulation test, serum calcitonin was <5 pg/mL using another kit. After we applied heterophilic blocking tubes, the serum calcitonin level decreased to normal range. We concluded that patient had spurious hypercalcitoninemia. In a 63-year-old woman, all tests revealed that the patient had true hypercalcitoninemia. The patient underwent total thyroidectomy that revealed MTC.
  
  
  CONCLUSIONS
  We suggest that patients suspected for spurious hypercalcitoninemia should undergo further investigation due to HAI.
authors.affiliation: Research Institute and Hospital, National Cancer Center, Gyeonggi, Korea.
authors.forename: Jung Min
authors.initials: JM
authors.lastname: Kim
authors.forename: Ki-Wook
authors.initials: KW
authors.lastname: Chung
authors.forename: Seok Won
authors.initials: SW
authors.lastname: Kim
authors.forename: Seon Hyeong
authors.initials: SH
authors.lastname: Choi
authors.forename: Hye Sook
authors.initials: HS
authors.lastname: Min
authors.forename: Ji-na
authors.initials: JN
authors.lastname: Kim
authors.forename: Woo-jae
authors.initials: WJ
authors.lastname: Won
authors.forename: Seok Ki
authors.initials: SK
authors.lastname: Kim
authors.forename: Ji In
authors.initials: JI
authors.lastname: Lee
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Chung
authors.forename: Sun Wook
authors.initials: SW
authors.lastname: Kim
mesh_terms: D000328:Adult; D000465:Algorithms; D000910:Antibodies, Heterophile / Q000097:blood / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000097:blood; D044963:Biopsy, Fine-Needle; D002116:Calcitonin / Q000097:blood*; D018276:Carcinoma, Medullary / Q000175:diagnosis; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D008875:Middle Aged; D011237:Predictive Value of Tests; D011379:Prognosis; D012680:Sensitivity and Specificity; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis* / Q000601:surgery; D016606:Thyroid Nodule / Q000097:blood / Q000175:diagnosis* / Q000601:surgery; D013965:Thyroidectomy; D013967:Thyroiditis, Autoimmune / Q000175:diagnosis; D016896:Treatment Outcome; D018084:Ultrasonography, Interventional
chemical_list: D000910:Antibodies, Heterophile; D014408:Biomarkers, Tumor; D002116:Calcitonin