Finding Hashimoto's takes more than the single TSH test most people get. The disease has a clear signature across a handful of markers — antibodies, hormone levels, and sometimes an ultrasound — and knowing which to ask for is half the battle.
The hallmark is thyroid-peroxidase antibodies (anti-TPO), positive in over 90% of cases and the test that actually names the autoimmune process — it can be raised 10–20 years before your TSH ever moves. Anti-thyroglobulin (anti-Tg) is less sensitive but catches some cases anti-TPO misses. Higher antibody levels signal faster progression (though not necessarily worse symptoms today). Evidence ●●●●●
TSH is the primary screen (it rises as the gland fails); free T4 tells you whether you've tipped from 'subclinical' (high TSH, normal T4) to 'overt' (high TSH, low T4). Free T3 and reverse T3 are where mainstream and functional medicine diverge: mainstream considers them unhelpful in an underactive thyroid, while functional practitioners test them to look for poor T4→T3 conversion. Reasonable to include, but read cautiously. Evidence ●●●●○ (TSH/T4) / ●●○○○ (reverse T3)
The disease moves through stages: antibody-positive but normal function → subclinical → overt hypothyroid. A thyroid ultrasound isn't needed to diagnose it, but it shows the characteristic damaged, patchy gland, and it guides a needle biopsy if a suspicious nodule turns up. Knowing your stage is what tells you whether to treat or simply monitor. Evidence ●●●●○
The panel to ask for
If you're symptomatic, request: TSH, free T4, anti-TPO, and anti-Tg — plus vitamin D, ferritin, and B12 to catch the deficiencies that mimic thyroid symptoms. Not TSH alone. That single addition — the antibodies — is what surfaces the disease years earlier.
The Hashimoto’s Guide