For a patient with a history of thyroid cancer the concentration of thyroglobulin and its trend over time are useful for monitoring disease recurrence or progression. Autoantibodies to thyroglobulin can interfere with immune-based assays, resulting in false-positive or false-negative results.
In many thyroid cancers the serum concentration of thyroglobulin reflects tumor burden. After total thyroidectomy the serum concentration should be unmeasurable in the absence of metastases or ectopic thyroid tissue. Reappearance of thyroglobulin indicates recurrence and rising levels disease progression.
Situations where an accurate measurement of thyroglobulin is important (Spencer and Wang):
(1) the patient is at high risk for recurrence
(2) the tumor's release of thyroglobulin is low (inefficient secretion)
(3) serum with a high level of thyroglobulin requiring dilution
Thyroglobulin measurements have had to deal with:
(1) high coefficient of variation (primarily in first-generation assays)
(2) low sensitivity (primarily in first-generation assays)
(3) interference from autoantibodies (in immune-based assays)
Methods such as LC MS/MS (liquid chromatography mass spectrometry) do not show interference from thyroglobulin autoantibodies, but these can be more expensive. One protocol (Powers et al) is to detect thyroid autoantibodies first; if autoantibodies are absent then a second-generation immunoassay is performed, else LC MS/MS.
