RESUMO
Context: Serum thyroglobulin (Tg) is a biochemical marker for detecting persistent or recurrent differentiated thyroid carcinoma (DTC) post-thyroidectomy. Tg can indicate DTC before structural disease (SD) is visible with imaging procedures. Objective: This work aimed to evaluate the clinical performance of the Elecsys® Tg II assay at a Tg cutoff of 0.2â ng/mL for ruling out SD in adults with DTC after total/near-total thyroidectomy, with or without radioiodine ablation (RAI). Methods: Patients were enrolled into 2 cohorts: longitudinal (Tg assessed every 6 months over 2 years under thyroid-stimulating hormone [TSH] suppression therapy following thyroidectomy with or without RAI) and cross-sectional with confirmed SD (Tg assessed once >12 weeks after thyroidectomy). Analyses were performed for both cohorts combined and in the longitudinal cohort. Results: The study included 530 clinically evaluable samples, the majority (n = 424 samples) from patients who had not received RAI treatment. Following correction for SD prevalence (4.97% in the longitudinal cohort), an Elecsys Tg II cutoff of 0.2â ng/mL ruled out SD with a negative predictive value of 99.9% (95% CI, 99.5%-100%). The assay had excellent sensitivity (98.5%-100%) and acceptable specificity (53.4%-53.5%) for detecting SD (Tg ≥ 0.2â ng/mL) for both cohorts combined and in the longitudinal cohort, with similar findings in RAI-treated and non-RAI-treated subgroups. Conclusion: In this cohort of DTC patients post-thyroidectomy, a Tg cutoff of 0.2â ng/mL was highly effective for ruling out the presence of SD under TSH-suppressed conditions, including in patients who had not received RAI treatment.
RESUMO
BACKGROUND: Untreated disorders of the adrenocortical system, such as Cushing's or Addison's disease, can be fatal, and accurate quantification of a patient's cortisol levels is vital for diagnosis. The objective of this study was to assess the analytical performance of a new fully-automated Elecsys® Cortisol II assay (second generation) to measure cortisol levels in serum and saliva. METHODS: Four European investigational sites assessed the intermediate precision and reproducibility of the Cortisol II assay (Roche Diagnostics) under routine conditions. Method comparisons of the Cortisol II assay vs. liquid chromatography-tandem mass spectrometry (LC-MS/MS), the gold standard for cortisol measurement, were performed. Cortisol reference ranges from three US sites were determined using samples from self-reported healthy individuals. RESULTS: The coefficients of variation (CVs) for repeatability, intermediate precision, and reproducibility for serum samples were ≤2.6%, ≤5.8%, and ≤9.5%, respectively, and for saliva were ≤4.4% and ≤10.9%, and ≤11.4%, respectively. Agreement between the Cortisol II assay and LC-MS/MS in serum samples was close, with a slope of 1.02 and an intercept of 4.473 nmol/L. Reference range samples were collected from healthy individuals (n=300) and serum morning cortisol concentrations (5-95th percentile) were 166.1-507 nmol/L and afternoon concentrations were 73.8-291 nmol/L. Morning, afternoon, and midnight saliva concentrations (95th percentile) were 20.3, 6.94, and 7.56 nmol/L, respectively. CONCLUSIONS: The Cortisol II assay had good precision over the entire measuring range and had excellent agreement with LC-MS/MS. This test was found suitable for routine diagnostic application and will be valuable for the diagnosis of adrenocortical diseases.
