Initial Workup and Lab Profile for Hashimoto's Thyroiditis
The initial workup for a patient suspected of having Hashimoto's thyroiditis should include thyroid function tests (TSH, free T4, free T3), thyroid autoantibodies (TPOAb and TgAb), and thyroid ultrasonography. 1
Laboratory Testing
Essential Laboratory Tests
Thyroid Function Tests:
- Thyroid-stimulating hormone (TSH)
- Free thyroxine (FT4)
- Free triiodothyronine (FT3) - particularly if TSH is abnormal
Thyroid Autoantibodies:
- Thyroid peroxidase antibodies (TPOAb) - present in 90-95% of Hashimoto's patients
- Thyroglobulin antibodies (TgAb) - present in 60-80% of Hashimoto's patients 2
Interpretation of Results
- Elevated TSH with normal or low FT4 indicates subclinical or overt hypothyroidism
- Positive TPOAb and/or TgAb with typical clinical features confirms Hashimoto's thyroiditis 3
- TgAb levels correlate with symptom burden in Hashimoto's patients, with higher levels associated with more symptoms like fragile hair, facial edema, eye edema, and harsh voice 4
Imaging Studies
- Thyroid Ultrasonography: Essential to evaluate for typical features of Hashimoto's thyroiditis 3
- Characteristic findings include:
- Diffuse hypoechogenicity
- Heterogeneous echotexture
- Reduced thyroid volume in advanced disease
- Increased vascularity
- Characteristic findings include:
Additional Workup
Complete Initial Assessment
- Complete blood count (CBC)
- Comprehensive metabolic panel including:
- Serum electrolytes (including calcium and magnesium)
- Blood urea nitrogen
- Serum creatinine
- Fasting blood glucose
- Lipid profile
- Liver function tests 3
Special Considerations
- Consider screening for other autoimmune conditions that may coexist with Hashimoto's:
- Parietal cell antibodies (associated with atrophic gastritis and pernicious anemia) 5
- Celiac disease markers
- Adrenal function tests if adrenal insufficiency is suspected
Monitoring and Follow-up
- For newly diagnosed patients, thyroid function tests should be repeated every 2-3 months initially
- Once stable (with or without levothyroxine therapy), monitoring can be reduced to every 6-12 months
- TPOAb levels typically decline during levothyroxine treatment but become negative in only about 16% of patients after long-term therapy 6
Clinical Pearls and Pitfalls
Important Clinical Considerations
- Hashimoto's thyroiditis can occasionally convert to Graves' disease, so unexplained improvement in hypothyroidism or need to decrease levothyroxine dose should prompt reevaluation 5
- Some patients may experience symptom burden despite normal thyroid function tests, which may correlate with antibody levels rather than TSH 4
- TSH receptor antibodies (TRAb) testing is not routinely indicated in Hashimoto's thyroiditis unless there are features suggesting Graves' disease 7
Potential Pitfalls
- Relying solely on TSH without measuring thyroid antibodies may miss the diagnosis in early stages
- Not all patients with positive thyroid antibodies develop hypothyroidism; approximately 10% of those with positive TPOAb and/or TgAb develop hypothyroidism 7
- Failure to recognize that some patients with Hashimoto's may have transient hypothyroidism with potential for recovery
By following this comprehensive workup approach, clinicians can accurately diagnose Hashimoto's thyroiditis and establish appropriate monitoring and treatment plans for affected patients.