Relationships between serum procalcitonin level, severity and different stresses of non-septic critically ill patients

Correction factor between two calcitonin assays: DiaSorin LiaisonXL and Cobas E601

Introduction: Calcitonin measurement is important for the diagnosis and monitoring of medullary thyroid carcinoma. Unfortunately, in clinical practice, different detection systems assays are used in the follow-up of the patients, which can be misleading.

Objective: To identify the correction factor for calcitonin measurement on two different immunoanalysers: DiaSorin-LiaisonXL (immunochemiluminescence) and CobasE601 (electro-immunochemiluminescence).

Methods: We selected 89 registered CT samples (28-from men; 61-from women), that were analysed on CobasE601 with reported values between 0.5 pg/ml and 2812 pg/ml (128.5±513.98). These CT samples were selected randomly to cover as wide a range of values as possible, and represented either basal CT (n=38) or selected from CT stimulation tests (n=51). Samples were evaluated subsequently on DiaSorin-LiaisonXL. All patients gave their informed consent.

Results: Between the two assays a segmented linear correlation was noted. We identified the following general linear regression equation: 1.108x+19.337 (p<0.05). The bias increased at high calcitonin values. Therefore, for a better accuracy we analysed the regression equation segmentally. A statistic difference (p<0.05) was noted for CT values ranged between 350-2600 pg/ml (n=31) on DiaSorin-LiaisonXL, for which the linear regression equation for CobasE601 becomes 1.009x+169.796.

Conclusions: Calcitonin correction factors are highly important in the dynamic follow up of a patient suffering from medullary thyroid carcinoma when different detection systems assays are used to determine calcitonin. We identified the correction factors for calcitonin determination between two different frequently used chemiluminescence immunoanalysers: DiaSorin-LiaisonXL and CobasE601. However, it is strongly advisable to use the same analyser in order to establish biochemical evolution of calcitonin.