Insights into the stability of serum calcitonin and a comparison of three serum calcitonin immunoassays.

[BACKGROUND] Medullary thyroid cancer (MTC) originates from parafollicular cells of the thyroid gland. These cells secrete calcitonin, which can be measured in serum using immunoassays to monitor MTC. The stability of calcitonin is not well understood and may affect serum calcitonin measurements. In addition, calcitonin immunoassays are poorly standardised, hindering comparison of calcitonin concentrations between assays. Here we aimed to gain insight in the stability of calcitonin in serum and in differences between calcitonin immunoassays.

[METHODS] The stability of calcitonin in serum was determined upon storage at room temperature for 5 h and upon five freeze-thaw cycles using the Liaison XL (Diasorin). Calcitonin method comparisons were performed using three immunoassays: Liaison XL, Cobas e601 (Roche Diagnostics) and Atellica IM 1300 (Siemens Healthineers).

[RESULTS] Changes in calcitonin concentrations in serum remain within the maximum allowable change criteria for up to 5 h at room temperature and five freeze-thaw cycles. Calcitonin method comparison showed good agreement between the Cobas e601 and Liaison XL (Calcitonin = 1.02 Calcitonin-1.64) assay. The Atellica IM 1300 assay agreed less with the Cobas e601 and Liaison XL assay (Calcitonin = 1.13Calcitonin + 2.59, Calcitonin = 1.13Calcitonin + 1.19).

[CONCLUSION] Calcitonin in serum remains stable for 5 h at room temperature and upon five freeze-thaw cycles. The method comparison between the Cobas e601 and Liaison XL showed good agreement, whereas the Atellica IM 1300 assay resulted in 13% higher concentrations than both Cobas e601 and Liaison XL. This highlights the importance of using the same immunoassay to monitor calcitonin concentrations in patients with MTC.