Procalcitonin interference in an immunometric calcitonin assay.
BACKGROUND
Procalcitonin (PCT) increases in septic patients, and is not transformed into calcitonin (CT). We found in septic patients, a significant increase of CT, as determined by an immunoassay using polyclonal antibodies. We compare determination using polyclonal and monoclonal AB.


METHODS
We included 34 patients: 17 with clinical signs of sepsis, a positive haemoculture (PCT > 0.5 μg/L) and 17 without them (PCT < 0.1 μg/L). CT was determined by two above-mentioned methods. The influence on CT levels was observed after using the high-concentration PCT calibrator addition to a mixed serum sample with a low concentration of CT. The dilution test of the high-concentration calibrator PCT was performed by an IBL calibrator, with a zero calcitonin concentration.


RESULTS
In the septic patients we found an interference in calcitonin determination using the polyclonal AB (IRMA); 24.1-718 μg/L, proportional to the PCT levels (r = 0.814, p < 0.0001). When using the monoclonal AB (ELISA), the calcitonin levels < 6.5-46.3 ng/L, and no interference of PCT was observed. In the non-septic group, we did not record any PCT interference using either the polyclonal or the monoclonal AB, and the CT levels were within the reference ranges using the two methods (r = 0.997, p < 0.0001). The recovery and dilution tests confirmed interference by PCT on the calcitonin determination with the polyclonal antibody.


CONCLUSIONS
Results show that in septic patients there is visible interference of PCT in the calcitonin determination, principally in the IRMA method (polyclonal AB); while no such relationship was observed in the ELISA method (monoclonal AB).
Institute of Clinical Biochemistry and Laboratory Diagnostics, First Faculty of Medicine and General Teaching Hospital, Charles University Prague, Czech Republic. jana.uhrova@vfn.cz
Jana
J
Uhrova
Helena
H
Brodska
Zdislava
Z
Vanickova
Hana
H
Benakova
Tomas
T
Zima
D000911:Antibodies, Monoclonal / Q000276:immunology; D002116:Calcitonin / Q000032:analysis*; D015740:Calcitonin Gene-Related Peptide; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D011498:Protein Precursors / Q000032:analysis*; D011933:Reagent Kits, Diagnostic; D012044:Regression Analysis
D000911:Antibodies, Monoclonal; C000606589:CALCA protein, human; D011498:Protein Precursors; D011933:Reagent Kits, Diagnostic; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide