A low TSH with elevated levels of T3 and T4 indicates an overactive thyroid, or hyperthyroidism. Hyperthyroidism occurs when thyroid hormone levels are elevated, which causes an increase in metabolism, and raises the risk of heart problems, bone loss, and pregnancy complications, explains eMedicineHealth.
The most common cause of hyperthyroidism is Grave’s disease, in which the immune system produces dysfunctional antibodies that mimic TSH, a hormone secreted by the pituitary gland. Under normal conditions TSH stimulates the thyroid to produce thyroid hormone and functions to regulate metabolism, according to WebMD.
In Grave’s disease, faulty antibodies produced by the immune system circulate in the blood stream and stimulate the gland to produce an excess amount of thyroid hormone. The constant stimulation of the thyroid can sometimes cause it to swell and cause a goiter, states Mayo Clinic.
The exact cause of Grave’s disease is not known; research suggests that heredity, environment and stress play important roles in its development. Studies show that identical twins have a 20 percent chance of developing Grave’s disease if one of the twins has it. Women are more likely to develop the disease, while smokers are more likely to develop eye problems associated with Grave’s, explains WebMD.