Clinical utility of serum thyroglobulin measurement

Abstract

Serum thyroglobulin (Tg) measurement is primarily used as a tumor marker to detect recurrent or persistent disease in patients with differentiated thyroid carcinomas. It is essential that clinicians interpret serum Tg values with respect to the patient-specific pathology and treatment and the technical limitations of the Tg method used. Important patient factors include the underlying thyroid pathology, the degree of any surgery and radioiodine therapy, and most importantly the TSH status of the patient at the time the blood specimen was drawn. Methodologic factors relate to the class of Tg method used: radioimmunoassay (RIA) or immunometric assay (IMA). Currently, most clinical laboratories use Tg IMA methods although such methods have well-recognized limitations that impact the clinical interpretation of serum Tg values. These limitations include wide between-method variability (which precludes the use of different Tg methods for serial monitoring of patients), inadequate sensitivity and suboptimal between-run precision (which impairs the early detection of recurrence), a propensity for “hook” problems (which can lead to underestimation of the very high serum Tg values typical of metastatic disease), and Tg autoantibody (TgAb) interference (which results in falsely low or undetectable serum Tg values in TgAb-positive patients with disease). This review will discuss how these patient and methodologic factors impact the clinical interpretation of serum Tg measurements.