Thyroglobulin (Tg) is composed of glycoprotein and the iodinated secretions of epithelial cells of the thyroid. These iodinated secretions contain both the precursors of T3 and T4 and the hormones themselves.
This test is helpful in the differential diagnosis of hyperthyroidism and in monitoring the course of differentiated or metastatic thyroid cancer. It is not useful in the diagnosis of thyroid cancer. Levels decrease following successful initial treatment, and in recurrence of metastases, the level will again rise. Lack of sensitivity and specificity limits the value of this test.
Adults: 3–42 ng/mL or 3–42 μg/L
Newborns (48 hours): 36–48 ng/mL or 36–48 μg/L
Eighty-seven percent of normal adults have serum values of Tg <10 ng/mL or <10 mg/L. Patients with athyrosis have values <5 ng/mL or <5 mg/L.
Obtain a 5-mL venous blood sample. Serum is needed.
Observe standard precautions. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered. Place the specimen in a biohazard bag.
Increased Tg levels are associated with the following conditions:
Untreated and metastatic differentiated thyroid cancers (not MTC)
Hyperthyroidism (not good correlation with elevated T4)
Subacute thyroiditis, thyrotoxicosis
Benign adenoma (some cases)
Occurrence of metastases after initial treatment (thyroid carcinoma)
Decreased Tg levels are associated with the following conditions:
Thyrotoxicosis factitia
Infants with goitrous hypothyroidism
Pretest Patient Care
See Patient Care for Thyroid Testing.
Ensure that patient is off thyroid medication for 6 weeks before specimen collection. The TSH should be elevated before testing for Tg.
Determination of Tg levels may be substituted for 131I scans in patients at low risk for thyroid cancer.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Resume thyroid medication and have patient resume normal activities. Review test results; report and record findings. Modify the nursing care plan as needed.
Monitor as appropriate for metastatic thyroid cancer.
Refer to patient aftercare instructions for thyroid testing. The same protocols prevail for Tg testing. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.