Screening Tests for Hashimoto's Thyroiditis
For patients suspected of having Hashimoto's thyroiditis, measure TSH as the primary screening test, followed by free T4 and anti-thyroid peroxidase (TPO) antibodies to confirm the diagnosis. 1
Initial Laboratory Testing Algorithm
Step 1: TSH Measurement
- TSH is the most sensitive screening test with 98% sensitivity and 92% specificity for detecting thyroid dysfunction 2, 1
- TSH values above 6.5 mU/L are considered elevated, though some evidence suggests a lower threshold of 2.6-2.9 mU/L may better identify Hashimoto's thyroiditis 2, 3
- A single elevated TSH requires confirmation, as 30-60% of elevated values normalize spontaneously on repeat testing 4
Step 2: Free T4 (FT4) Measurement
- Measure free T4 simultaneously with TSH to distinguish between subclinical hypothyroidism (normal FT4) and overt hypothyroidism (low FT4) 4, 1
- This combination determines disease severity and guides treatment decisions 1
Step 3: Anti-TPO Antibodies
- Measure anti-TPO antibodies to confirm autoimmune etiology of thyroid dysfunction 4, 1
- Positive TPO antibodies identify patients at higher risk of progression to overt hypothyroidism (4.3% per year versus 2.6% in antibody-negative individuals) 4, 1
- TPO antibodies are the most specific marker for Hashimoto's thyroiditis 1
Additional Antibody Testing
Anti-Thyroglobulin (TgAb) Antibodies
- Consider measuring TgAb in patients with symptom burden despite normal TSH and negative TPO antibodies 5
- Elevated TgAb levels correlate with increased symptom burden, including fragile hair, face edema, eye edema, and harsh voice 5
- TgAb positivity (with or without TPO antibodies) confirms Hashimoto's thyroiditis 1
Confirmation Testing Protocol
Repeat Testing Timeline
- If TSH is elevated on initial testing, repeat TSH and free T4 after 3-6 weeks to confirm the diagnosis 4
- This interval accounts for transient causes of TSH elevation including acute illness, recent iodine exposure, recovery from thyroiditis, or certain medications 4
High-Risk Populations Requiring Screening
The USPSTF identifies specific groups with higher screening yield, though routine screening of asymptomatic adults is not recommended 2:
- Postpartum women: Subclinical hypothyroidism is associated with poor obstetric outcomes and poor cognitive development in children 2
- Elderly patients: Prevalence increases with age, reaching up to 5% in women and 3% in men 2
- Patients with Down syndrome: Higher risk for thyroid dysfunction, though evaluating symptoms is complicated by overlapping clinical features 2
- Patients with high radiation exposure (>20 mGy): Increased risk of thyroid dysfunction 2
Critical Pitfalls to Avoid
- Never treat based on a single elevated TSH value without confirmation testing, as 30-60% normalize spontaneously 4
- Do not rely on TSH alone in patients with pituitary disease or suspected central hypothyroidism, as TSH may be inappropriately normal despite low free T4 4
- Avoid missing thyroid hormone autoantibody (THAAb) interference, which can cause falsely abnormal thyroid function results; if results are inconsistent with clinical presentation, retest on different platforms or use polyethylene glycol (PEG) precipitation 6
- Do not overlook TgAb testing in symptomatic patients with negative TPO antibodies, as TgAb positivity alone can confirm Hashimoto's thyroiditis and correlates with symptom burden 5
When Screening is NOT Recommended
The USPSTF concludes that evidence is insufficient to recommend for or against routine screening for thyroid disease in asymptomatic adults, as the positive predictive value of TSH in primary care populations is low and treatment benefits for screen-detected disease are uncertain 2