Most people who have Hashimoto's disease -approximately 90% - have antibodies that can be measured in the blood. The Thyroid Peroxidase Antibodies (TPO) test detects those antibodies.
At the same time, around 5% of people who have the disease and were diagnosed by other means (i.e., ultrasound, biopsy, etc.) do not have measurable thyroid antibodies.
In one study, researchers looked at patients who had been diagnosed with Hashimoto's thyroiditis, but had no measurable antibodies. This group was compared to patients who had Hashimoto's and antibodies.
What they found was that overt hypothyroidism — defined as an elevated thyroid stimulating hormone (TSH) level, and low Free Thyroxine (Free T4) levels was more common in those patients who tested positive for thyroid antibodies. Subclinical hypothyroidism — mildly increased TSH — was more common in the group who did not test positive for antibodies. The researchers concluded that the presence of antibodies was more associated with overt hypothyroidism, and thyroid enlargement. Hashimoto's without antibodies was associated with milder, subclinical hypothyroidism. Additionally, it was concluded that treating patients with subclinical hypothyroidism and positive thyroid antibodies could prevent the development of overt hypothyroidism.
What This Means for You and Your Hashimoto's Thyroiditis?
First, this makes it clear that you can have Hashimoto's disease, even if you test negative for TPO antibodies. This goes against some of the standard dogma of conventional medicine, which claims that only those who have elevated TPO antibodies can be diagnosed with Hashimoto's disease.
Next, as the study suggested, treating even subclinical hypothyroidism in Hashimoto's — whether confirmed by antibodies testing or not — may prevent progression to overt hypothyroidism.
This provides more ammunition to the position that integrative physicians have had for years — that treating patients who have thyroid antibodies with normal reference range thyroid levels, or those with mild hypothyroidism, can benefit those patients by preventing them from becoming overtly hypothyroid.
Source: Rotondi M et al. "Serum negative autoimmune thyroiditis displays a milder clinical picture compared with classic Hashimoto's thyroiditis." European Journal of Endocrinology, 2014;171:31-6. April 17 2014