Vitros 950

Before 1997, both pentagastrin-stimulated calcitonin levels and basal serum calcitonin levels were measured by radioimmunoassay. After 1997, calcitonin levels were measured by immunoluminometric assay and since April 2006, an immunoradiometric assay (CisBio Bioassays) is used. The appropriate reference levels for each method were used to determine whether the calcitonin levels were normal or elevated.
During the study period, both serum Ca and/or serum ionized Ca (iCa) levels have been measured to evaluate occurrence of hypoparathyroidism after surgery. Serum Ca was measured until 2006 with a Vitros950 (Ortho clinical diagnostics), followed by DxC (UniCel 600 DxC ; Beckman Coulter) until 2012 and since then an AU5811 (Beckman Coulter). Since the introduction in 2003, iCa has been measured by an ion selective electrode on a blood gas analyzer. For both measurements, the laboratory units were consistent from 1993 onwards.
All patients were screened for RET mutation in the National laboratory for Genetics at the UMCU. PCR amplification followed by direct sequence analysis of exons 10–16 of the RET proto-oncogene was used to determine the exact type of mutation. RET mutation was thereafter confirmed on a DNA duplicate sample. The affected codon was used to stratify patients into 3 risk groups according to the 2015 ATA guidelines to define age-appropriate surgery.^{4 (link)}