title: Procalcitonin: a marker for the diagnosis and follow-up of patients with medullary thyroid carcinoma.
abstract: BACKGROUND
  Calcitonin (CT) is the main medullary thyroid carcinoma (MTC) tumor marker. However, it has several limitations, including a concentration-dependent biphasic half-life, sensitivity to rapid in vitro degradation, and the presence of different isoforms/fragments. Procalcitonin (PCT), the prohormone of calcitonin, is free of these limitations but is currently used only as a sepsis marker.
  
  
  OBJECTIVE
  The objective of the study was to determine whether PCT is suited as a MTC tumor marker by comparing the diagnostic performance of PCT with that of CT in MTC.
  
  
  METHODS
  PCT and CT were measured in a total of 835 subjects, including normal volunteers (n = 197) and patients with active-MTC (n = 91), cured-MTC (n = 42), neuroendocrine tumors (n = 225), mastocytosis (n = 48), follicular cell-derived thyroid carcinoma (cured = 120, persistent/recurrent = 55), and benign thyroid disease (n = 57).
  
  
  RESULTS
  PCT levels were significantly higher in the active-MTC patients (mean 126.4 ng/ml) than the cured-MTC patients (mean <0.1 ng/ml). The overall concordance between the two markers was 95.7% (kappa = 0.81). Receiver-operating characteristic curve analysis showed no significant difference in diagnostic performance between CT and PCT. PCT's diagnostic sensitivity and specificity were 91 and 96%, respectively. The corresponding values for CT were 99 and 98%. Analyte stability studies showed that CT is very unstable in vitro with a decrease of 35-50% from the original value 24 h after the blood draw, whereas PCT levels did not significantly change during this time.
  
  
  CONCLUSIONS
  A strong correlation was observed between PCT and CT levels in patients with MCT. Given PCT's greater analytical stability, we conclude that it represents a promising complementary MTC tumor marker.
authors.affiliation: Department of Laboratory Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: Algeciras-Schimnich
authors.forename: Carol M
authors.initials: CM
authors.lastname: Preissner
authors.forename: J Paul
authors.initials: JP
authors.lastname: Theobald
authors.forename: Mary S
authors.initials: MS
authors.lastname: Finseth
authors.forename: Stefan K G
authors.initials: SK
authors.lastname: Grebe
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000097:blood*; D002116:Calcitonin / Q000097:blood*; D015740:Calcitonin Gene-Related Peptide; D018276:Carcinoma, Medullary / Q000097:blood / Q000175:diagnosis*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011498:Protein Precursors / Q000097:blood*; D012016:Reference Values; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000097:blood / Q000175:diagnosis*
chemical_list: D014408:Biomarkers, Tumor; C000606589:CALCA protein, human; D011498:Protein Precursors; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide