Laboratory Testing for Papillary Thyroid Carcinoma

Initial Diagnostic Phase

Thyroid function tests, including TSH, should be obtained during the diagnostic workup of a thyroid nodule suspicious for papillary thyroid carcinoma, although they have limited diagnostic value for detecting malignancy itself 1, 2
Thyroglobulin measurement is not helpful for initial diagnosis of thyroid cancer 1, 2
Serum calcitonin should be measured as part of the diagnostic evaluation to rule out medullary thyroid cancer, as it has higher sensitivity than fine needle aspiration for this subtype 1, 2, 3

The first laboratory assessment, 2-3 months after initial treatment, should include TSH, FT3, and FT4 to verify adequate levothyroxine suppressive therapy 4, 5, 6, 7, 8, 9, 10
At 6-12 months after initial treatment, basal serum Tg and rhTSH-stimulated serum Tg should be measured, along with anti-thyroglobulin antibodies (TgAb), to determine disease-free status 4, 5, 6, 7, 8, 9, 10
Undetectable stimulated Tg (<1.0 ng/ml) with negative TgAb and normal neck ultrasound indicates complete remission with <1% recurrence risk at 10 years 4, 5, 6, 7, 8, 9, 10

For patients in complete remission after initial assessment, basal serum Tg on LT4 therapy should be measured annually, along with TSH to monitor adequacy of thyroid hormone replacement 4, 6, 7, 8, 9, 10

Never rely on basal Tg alone without TSH stimulation for the initial 6-12 month assessment, as stimulated Tg is far more sensitive for detecting residual disease 4, 5, 6, 7, 8
Always measure TgAb concurrently with Tg, as 25% of patients may have interfering antibodies 4
Do not use Tg for initial diagnosis of thyroid nodules—it has no diagnostic value in this setting 1, 2