What is the initial workup for a patient suspected of having Hashimoto's (Hashimoto's thyroiditis)?

Initial Workup for Hashimoto's Thyroiditis

The initial workup for a patient suspected of having Hashimoto's thyroiditis should include thyroid function tests (TSH and free T4) and thyroid autoantibody testing (thyroid peroxidase antibodies [TPOAb] and thyroglobulin antibodies [TgAb]). 1, 2

Laboratory Testing

Primary Tests:

• TSH and Free T4: These are the cornerstone tests for evaluating thyroid function in suspected Hashimoto's thyroiditis 1, 3
  • TSH is the most sensitive indicator of thyroid function (reference range typically 0.4-5.0 μIU/mL)
  • Free T4 helps distinguish between primary and central hypothyroidism
  • Low TSH with low Free T4 suggests central hypothyroidism and requires evaluation for hypophysitis 1

Autoantibody Testing:

• Thyroid Peroxidase Antibodies (TPOAb): Present in 90-95% of Hashimoto's patients
• Thyroglobulin Antibodies (TgAb): Less sensitive but adds diagnostic value when TPOAb is negative

Clinical Evaluation

• Thyroid Examination: Assess for diffuse, firm, non-tender goiter (characteristic of Hashimoto's)
• Symptom Assessment: Evaluate for hypothyroid symptoms including fatigue, cold intolerance, weight gain, constipation, dry skin, and hair loss
• Family History: Document any family history of thyroid disorders or other autoimmune conditions

Additional Considerations

Monitoring Recommendations:

• For patients with normal thyroid function but positive antibodies (euthyroid Hashimoto's):
  • Monitor TSH and Free T4 every 6-12 months 4
  • 21.1% of initially euthyroid patients may develop hypothyroidism during follow-up 4

Differential Diagnosis:

• Be aware that Hashimoto's thyroiditis can occasionally convert to Graves' disease (hyperthyroidism) 5
• This conversion typically occurs about 38 ± 45 months after Hashimoto's diagnosis
• Suspect this conversion if a patient on levothyroxine requires decreasing doses or develops hyperthyroid symptoms 5

Treatment Approach

• For patients with overt hypothyroidism (elevated TSH with low Free T4):

  • Initiate thyroid hormone replacement therapy (levothyroxine)
  • Starting dose based on weight, age, and comorbidities 2
  • Lower starting doses (25-50 μg/day) for elderly patients or those with cardiac disease 2

• For subclinical hypothyroidism (elevated TSH with normal Free T4):

  • Treatment generally recommended when TSH persistently >10 mIU/L 1
  • Consider treatment at lower TSH levels if symptomatic

Common Pitfalls

• Pitfall #1: Failing to test both TSH and Free T4 together

  • TSH alone may miss central hypothyroidism 1
  • In hypophysitis, TSH can remain within normal range despite hypothyroidism 1

• Pitfall #2: Not recognizing the dynamic nature of Hashimoto's thyroiditis

  • Thyroid function can fluctuate over time 4
  • Regular monitoring is essential even after diagnosis

• Pitfall #3: Missing other autoimmune conditions

  • Hashimoto's patients have increased risk of other autoimmune disorders
  • Consider screening for celiac disease, pernicious anemia, or adrenal insufficiency in appropriate clinical contexts

Remember that Hashimoto's thyroiditis is a chronic condition requiring long-term monitoring, as thyroid function can change over time, with some patients experiencing recovery of thyroid function while others progress to permanent hypothyroidism 4, 6.