Thyroxine - Total (TT4)

Normal total thyroxine (TT4) in adults is roughly 5–12 µg/dL (64–154 nmol/L). Reference ranges can vary by laboratory, age and pregnancy; changes in binding proteins, medications or illness affect total T4. TT4 should be interpreted alongside TSH and free T4. If your result is outside the local reference range or you have symptoms, consult your healthcare provider.

If total T4 (TT4) is high, it often indicates excess thyroid hormone—commonly hyperthyroidism—which can cause weight loss, rapid heartbeat, tremor, heat intolerance, anxiety, increased appetite, and sleep problems. It may reflect raised thyroid-binding proteins (pregnancy, estrogen) or a lab artifact. High TT4 with suppressed TSH supports hyperthyroidism; persistent excess risks atrial fibrillation and osteoporosis and needs medical evaluation. Free T4 is more clinically relevant.

TT4 stands for total thyroxine, the combined amount of protein-bound and free T4 in the blood. It reflects thyroid hormone production and binding‑protein levels. Elevated TT4 can occur with hyperthyroidism, pregnancy, or increased binding proteins; low TT4 may indicate hypothyroidism, low binding proteins (e.g., nephrotic syndrome), or nonthyroidal illness. TT4 is interpreted alongside TSH and free T4.

When thyroxine (T4) is low, metabolism slows causing fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, slowed heart rate and depression. In women it can cause heavier periods and infertility; in children, growth and developmental delays. Blood tests often show elevated TSH in primary hypothyroidism. Untreated, low T4 can raise cholesterol and, rarely, progress to life‑threatening myxedema coma.

Yes. Acute and chronic stress alter the hypothalamic–pituitary–adrenal axis, which can reduce total T4 and modify peripheral conversion of T4 to T3, increasing reverse T3. Free T4 is usually minimally changed, but stress can transiently affect thyroid blood tests and symptoms. Stress doesn't typically cause primary thyroid disease, but it can complicate interpretation of thyroid function tests and clinical management.

High T4 (hyperthyroidism) commonly causes weight loss despite increased appetite, heat intolerance and excessive sweating, rapid or irregular heartbeat (palpitations), tremors, anxiety or irritability, nervousness, and difficulty sleeping. People may also experience muscle weakness, fatigue, more frequent bowel movements or diarrhea, thinning hair, and menstrual irregularities. Long-term untreated hyperthyroidism can increase fracture risk and worsen cardiovascular problems.