Amber Mater1, Anita Boelen1, Pim de Graaf2, Koen M. A. Dreijerink3, Annemieke C. Heijboer1, Jacquelien J. Hillebrand1
(1) Department of Laboratory Medicine, Endocrine Laboratory, Amsterdam UMC, Amsterdam, The Netherlands.
(2) Department of Radiology and Nuclear Medicine, Amsterdam UMC, Amsterdam, The Netherlands.
(3) Department of Endocrinology and Metabolism, Amsterdam UMC, Amsterdam, The Netherlands.
Background
Diagnosis of medullary thyroid cancer is mostly based on cytological examination of ultrasound guided fine needle aspiration (FNA) biopsies taken from suspicious lesions. Unfortunately, the sensitivity of these examinations is suboptimal. Therefore, (inter)national guidelines recommend to measure calcitonin in FNA washout upon inconclusive cytology results. However, the lack of (pre-)analytical validation studies is hampering the routine application of calcitonin measurement in FNA washout.
Objective
To validate the suitability of three solvents (CytoLyt, NaCl and diluent) as collection solvent for use in measuring calcitonin in FNA washout, focusing on (pre-)analytical aspects.
Methods
Precision (inter- and intra-assay coefficients of variation (CV)), accuracy (linearity and recovery) and storage stability of each solvent were assessed after spiking with calcitonin standard. Calcitonin measurements were performed using the serum CALCT immunoassay (Siemens, Atellica). Decision criteria were set based on CLSI and manufacturer’s manual.
Results
Measurements of calcitonin in diluent met all decision criteria: inter- and intra-assay CVs were ≤ 9% and ≤ 5.5%, serial dilutions were linear (R = 0.996) and median recovery was 148% with limited variation. Furthermore, calcitonin concentrations remained stable (<10%) after storage. Measurements in CytoLyt were precise and accurate, but unstable upon storage. Measurements in NaCl only met the criteria for intra-assay CV and linearity.
Conclusion
This study showed that assay diluent was the optimal solvent to use for calcitonin measurements in a non-serum matrix. CytoLyt performed suboptimal, while the performance of NaCl was poor. Further research is needed to validate the recommended work-up using patient-derived material.