The Utility of Serum Thyroglobulin Measurement at the Time of Remnant Ablation for Predicting Disease-Free Status in Patients with Differentiated Thyroid Cancer: A Meta-Analysis Involving 3947 Patients

Decisions regarding initial therapy and subsequent surveillance in patients with differentiated thyroid cancer (DTC) depend upon an accurate assessment of the risk of persistent or recurrent disease. The objective of this study was to examine the predictive value of a single measurement of serum thyroglobulin (Tg) just before radioiodine remnant ablation (preablation Tg) on subsequent disease-free status. Sources included MEDLINE and BIOSYS databases between January 1996 and June 2011 as well as data from the author's tertiary-care medical center. Included studies reported preablation Tg values and the outcome of initial therapy at surveillance testing or during the course of long-term follow-up. Two investigators independently extracted data and rated study quality using the Quality Assessment of Studies of Diagnostic Accuracy included in Systematic Reviews-2 (QUADAS-2) tool. Fifteen studies involving 3947 patients with DTC were included. Seventy percent of patients had preablation Tg values lower than the threshold value being examined. The negative predictive value (NPV) of a preablation Tg below threshold was 94.2 (95% confidence interval = 92.8–95.3) for an absence of biochemical or structural evidence of disease at initial surveillance or subsequent follow-up. The summary receiver operator characteristic curve based on a bivariate mixed-effects binomial regression model showed a clustering of studies using a preablation Tg below 10 ng/ml near the summary point of optimal test sensitivity and specificity. Preablation Tg testing is a readily available and inexpensive tool with a high NPV for future disease-free status. A low preablation Tg should be considered a favorable risk factor in patients with DTC. Further study is required to determine whether a low preablation Tg may be used to select patients for whom radioiodine remnant ablation can be avoided.