Diagnostic Testing for Hashimoto's Thyroiditis
The diagnosis of Hashimoto's thyroiditis requires measurement of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and thyroid autoantibodies—specifically thyroid peroxidase antibodies (TPO-Ab) and thyroglobulin antibodies (TgAb)—with the autoantibodies being the definitive markers that confirm the autoimmune nature of the disease. 1
Initial Laboratory Panel
The cornerstone diagnostic approach involves simultaneous measurement of:
TSH and FT4: These should be measured together as the primary assessment of thyroid function 1. TSH is the most reliable indicator of thyroid status, with reference ranges typically 0.4-5.0 mIU/L 2. TSH has sensitivity above 98% and specificity greater than 92% when used to confirm suspected thyroid disease 3.
Thyroid Peroxidase Antibodies (TPO-Ab): This is the hallmark autoantibody for Hashimoto's thyroiditis and should be tested in all suspected cases 1. TPO-Ab is present in approximately 80% of Hashimoto's patients 4.
Thyroglobulin Antibodies (TgAb): This second autoantibody marker is critical for confirming autoimmune thyroid disease 1. TgAb positivity correlates with symptom burden in Hashimoto's patients, including symptoms like fragile hair, facial edema, eye edema, and harsh voice 5.
Additional Testing Considerations
Free T3 (FT3): Consider measuring FT3 when TSH and FT4 results are discordant or when patients remain highly symptomatic despite normal TSH/FT4 values 1.
TSH Receptor Antibodies (TRAb): These are not routinely needed for Hashimoto's diagnosis but are essential when differentiating Graves' disease from Hashimoto's thyroiditis in patients presenting with hyperthyroidism 2, 6.
Clinical Context for Testing
Testing should be pursued in patients with:
- Signs or symptoms suggestive of thyroid dysfunction 3
- High-risk features: female sex, age >60 years, family history of thyroid disease, personal history of autoimmune disease, type 1 diabetes, previous thyroid dysfunction, or history of head/neck radiation 3
- Palpable thyroid abnormalities or goiter 3
Important Testing Pitfalls
Avoid these common errors:
False TSH elevations: Heterophilic antibodies can cause falsely elevated TSH in some assays 1. Medications like glucocorticoids and dopamine can suppress TSH levels 1.
Severe non-thyroid illness: Acute illness can produce false-positive TSH results, with positive predictive values as low as 0.06 for hypothyroidism in hospitalized patients 3.
Timing considerations: Multiple TSH measurements over 3-6 months may be needed to confirm persistent abnormalities, as mild TSH elevations often normalize spontaneously 3.
Pregnancy effects: Total T4 (TT4) is unreliable during pregnancy due to elevated thyroid-binding globulin; always use FT4 instead 2.
Monitoring After Diagnosis
Once Hashimoto's is confirmed and treatment initiated: