RESUMEN
CONTEXT: Treatment and follow-up of patients thyroidectomized for differentiated thyroid carcinoma (DTC) mainly depends on the identification of the patient's risk of recurrence. Thyroglobulin (Tg) is the most important marker of persistent/recurrent disease. The recent introduction of a new, more sensitive Tg measurement allows for the early detection of the disease by measuring the basal (under L-T(4) therapy) serum Tg level without TSH stimulation. OBJECTIVE: The goal of this study is to identify the basal serum Tg threshold value that indicates recurrent disease by using a second-generation Tg assay. DESIGN AND PATIENTS: A continuous series of 425 DTC patients, all thyroidectomized and treated with (131)I after surgery and having basal Tg of no more than 1.0 ng/ml, negative anti-Tg antibodies, and a recombinant human TSH-stimulated Tg measurement was retrospectively analyzed. SETTING: The study took place at an academic hospital. RESULTS: The most accurate basal Tg value for predicting the presence of recurrent/residual disease was more than 0.15 ng/ml (sensitivity 87%, specificity 91%, negative predictive value 98.6%, and positive predictive value 47.8%). When the basal Tg level was no more than 0.15 ng/ml, the risk of disease presence was very low, even in patients classified at an intermediate or high risk. In contrast, when the basal Tg level was more than 0.15 ng/ml, the percentage of recurrent disease was relatively high (12.5% or one in eight cases) in low-risk patients. CONCLUSIONS: Basal Tg, measured using a second-generation Tg assay allows for the identification of DTC patients who are likely to remain disease free with great accuracy. This simple measurement, therefore, may be sufficient to assess the risk-adapted management of DTC patients.