1. Routine laboratory tests
The purpose is to understand the general condition of the patient and the need for appropriate therapeutic measures, including blood routine, liver and kidney function, thyroid function, etc. If invasive tests or surgical treatment are required, coagulation and viral indicators are also required. For patients with DTC who need to suppress thyroid stimulating hormone (TSH) to below the lower limit of the normal reference range (especially postmenopausal women), the pre-treatment basal bone mineralization status should be evaluated and monitored regularly as appropriate according to medical conditions; serum calcium/phosphorus, 24-hour urine calcium/phosphorus, and biochemical markers of bone conversion are available.
2. Thyroid hormone, thyroid autoantibodies and tumor marker tests
(1) Thyroid hormone test: including thyroxine (T4), triiodothyronine (T3), free thyroxine (FT4) and free triiodothyronine (FT3) and TSH measurement in blood. TSH testing is an important initial screening test to clarify thyroid function. In patients with thyroid cancer treated with TSH suppression, blood thyroid hormone levels also need to be tested regularly and levo-thyroxine (L-T4) adjusted according to the test results.
(2) Thyroid autoantibodies: autoantibodies associated with autoimmune thyroid disease include anti-thyroglobulin antibodies (TgAb), thyroid peroxidase antibodies (TPOAb), and TSH receptor antibodies (TgAb), thyroid peroxidase antibodies (TPOAb) and TSH receptor antibody (TRAb). In patients with DTC, TgAb is an important ancillary test for thyroglobulin (Tg). Serum Tg levels are also affected by TgAb levels, which, when present, can reduce the value of serum Tg detected by chemiluminescent immunoassay methods and affect the accuracy of monitoring the condition by Tg. Thyroid peroxidase (TPO) is a key enzyme in the synthesis of thyroid hormones, and the presence of TPOAb usually precedes thyroid dysfunction and is involved in the tissue destruction process in the development of Hashimoto’s thyroiditis and atrophic thyroiditis, causing clinical symptoms of hypothyroidism. A positive TRAb test result indicates the presence of autoantibodies against the TSH receptor.
(3) Thyroglobulin (Tg), calcitonin, and carcinoembryonic antigen (CEA) are specific proteins produced by the thyroid gland, but serum Tg measurement lacks specific value in identifying benign and malignant thyroid nodules. Therefore, serum Tg measurement is generally not used clinically for the preoperative diagnosis of DTC. in the follow-up phase of DTC patients after treatment, serum Tg changes are an important tool to discern whether the patient has tumor recurrence, and serum Tg can be used to monitor recurrence and metastasis after DTC surgery. For patients with DTC who have removed all thyroid tissues, elevated serum Tg indicates the possibility of tumor recurrence and should be further examined. For patients with DTC without complete thyroid removal, it is still recommended to measure serum Tg periodically (every 6 months) after surgery, and those with persistently elevated serum Tg levels after surgery should consider thyroid tissue or tumor growth, which should be further evaluated in combination with other tests such as neck ultrasound. Tg measurement after TSH stimulation (TSH > 30 mU/L). To more accurately reflect the condition, serum TSH levels can be increased to >30 mU/L by discontinuing L-T4 or applying recombinant human thyrotropin (rhTSH), followed by a Tg assay, i.e., post-TSH stimulation Tg measurement. Tg levels measured after discontinuation of L-T4 and use of rhTSH were highly concordant. Patients with DTC stratified as intermediate or high risk of recurrence may be tested for post-TSH stimulation Tg if necessary.
It should be noted that Tg should be measured at the same time as TgAb. If TgAb is elevated, the presence or absence of recurrence of DTC cannot be determined by Tg. If DTC cells are poorly differentiated, cannot synthesize and secrete Tg or produce defective Tg, follow-up with Tg is also not possible. Measurement of Tg levels in lymph node puncture needle eluate for suspicious cervical lymph nodes palpable on examination and detected by ultrasound can improve the sensitivity of detecting DTC lymph node metastases.
Patients with MTC are recommended to have both serum calcitonin and CEA measured before treatment and to monitor changes in serum levels periodically after treatment. If the levels exceed the normal range and continue to increase, especially when calcitonin ≥150 pg/ml, progression or recurrence of the disease should be highly suspected. Serum calcitonin and CEA tests are useful for the assessment of the efficacy and monitoring of the disease in patients with medullary carcinoma.
(4) Relevant molecular tests for diagnosis: for thyroid nodules whose benignity or malignancy cannot be determined by fine-needle aspiration (FNA), molecular marker testing of the puncture specimen, such as BRAF mutation, RAS mutation, RET/PTC rearrangement, etc., can be performed to help improve the confirmation rate. The detection of BRAF mutation status in preoperative puncture specimens also helps in the diagnosis and clinical prognosis prediction of papillary thyroid cancer, which facilitates the development of individualized diagnosis and treatment plans.