What Does Low TSH and Normal T3 and Normal T4 Mean?

Some patients with low TSH combined with normal levels of T3 and T4 eventually develop overt thyroid disease, but clinical assessment and management needs to be tailored to each patient, according to Thyroid Foundation of Canada. Typically, low or suppressed TSH combined with high levels of T4 or T3 indicates hyperthyroidism. Abnormally high TSH in conjunction with low T4 is usually a sign of hypothyroidism.

TSH is released by the pituitary gland to stimulate and regulate thyroid production of the hormones T3 and T4. When thyroid levels decrease, TSH production increases and vice versa. An abnormal TSH reading is believed to indicate thyroid disease, according to Thyroid Foundation of Canada, but there are exceptions.

Research shows that unusual results on TSH tests combined with normal levels of serum hormones T3 and T4 could be related to a nonthyroidal illness, according to Medscape. After the patient recovers, thyroid function tests should return to normal.

Symptoms of true hypothyroidism, or low thyroid production, include dry skin, fatigue, poor appetite, intolerance to cold, constipation and muscle weakness. Symptoms of hyperthyroidism, or overactive thyroid, include weight loss, accelerated or irregular heartbeat, and irritability, according to Mayo Clinic. True hypothyroidism and hyperthyroidism are both treatable with medication, radioactive iodine or surgery.