Context: 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.
Objective: 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.
Data sources: Sources included MEDLINE and BIOSYS databases between January 1996 and June 2011 as well as data from the author's tertiary-care medical center.
Study selection: Included studies reported preablation Tg values and the outcome of initial therapy at surveillance testing or during the course of long-term follow-up.
Data extraction: 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.
Data synthesis: 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.
Conclusion: 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.