Distinguishing autoimmune thyroid disease is difficult in its early stages. Both may have low TSH initially. Graves' disease has a low TSH due to overactive thyroid
Early-stage Hashimoto's typically has low TSH due to early Hashitoxicosis, which is the initial stage of hyperthyroidism. However, as Hashimoto's progresses, the hyperthyroidism decreases, and the TSH level increases as the disease progresses and the body moves more and more into a state of hypothyroidism.
Thyroid antibody tests & radioactive iodine uptake help differentiate between the two.
CLICK HERE to learn more about how to differentiate Grave's disease from Hashimoto's using blood biomarkers