Thyroid Biomarker
Collection Type: Blood
Related System: Thyroid
Free T4 (free thyroxine) is the unbound fraction of the thyroid hormone thyroxine circulating in blood; it is the biologically active form available to tissues. The Free T4 test measures the concentration of this unbound hormone to assess thyroid gland function and help diagnose hyperthyroidism or hypothyroidism, thyroiditis, and to monitor replacement or antithyroid therapy. Common reasons to test include unexplained weight change, fatigue, palpitations, temperature intolerance, hair loss, tremor, menstrual irregularities, or developmental concerns in children. Levels vary with age (newborns/infants have higher values; elderly may trend lower), pregnancy (binding changes may affect total but can influence free measurements), medications, and severe acute illness.
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Symptom Checker0.8-1.8 ng/dL OR 10-23 pmol/L
Q: What does T4 thyroxine free mean?
A: Free T4 (T4 thyroxine free) is the unbound portion of the thyroid hormone thyroxine circulating in blood that is biologically active and available to tissues. Measuring free T4 helps assess thyroid function—low levels suggest underactive thyroid (hypothyroidism), high levels indicate overactive thyroid (hyperthyroidism). It’s preferred over total T4 because it isn’t affected by blood binding proteins.
Q: What is a good T4 level for a woman?
A: A healthy adult woman’s free T4 typically falls about 12–22 pmol/L (0.9–1.7 ng/dL); total T4 reference is roughly 5–12 µg/dL. Lab-specific ranges vary, and results must be interpreted with TSH and clinical signs what’s “good” depends on symptoms, pregnancy and medications. Discuss abnormal results with your clinician for diagnosis and management. Regular monitoring is recommended.
Q: What happens if your free T4 is low?
A: If your free T4 is low, you may develop hypothyroid symptoms: fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, slowed thinking and a slower heart rate. Low FT4 with high TSH usually means primary thyroid failure; low/normal TSH suggests pituitary/hypothalamic causes. Untreated, it can raise cholesterol and cardiovascular risk; treatment is typically levothyroxine with regular monitoring.
Q: What if free T4 is high?
A: A high free T4 usually indicates thyroid overactivity (hyperthyroidism) from causes like Graves’ disease, toxic nodules, thyroiditis, or excess thyroid medication. Symptoms include weight loss, palpitations, heat intolerance, tremor and often a low TSH. Repeat testing, check TSH and antibody levels, review medications, and see your doctor for diagnosis and treatment (antithyroid drugs, radioactive iodine, or surgery) as needed.
Q: What are symptoms of low T4 thyroid?
A: Low T4 (hypothyroidism) commonly causes fatigue, unexplained weight gain, sensitivity to cold, constipation, dry skin and hair loss, slowed heart rate, muscle weakness and cramps, depression or low mood, memory and concentration problems, heavy or irregular menstrual periods, hoarseness, puffy face and swelling, and elevated cholesterol. Symptoms develop gradually and vary in severity.
Q: How to reduce T4 levels?
A: To lower elevated T4 you need medical evaluation. Treatments include adjusting or stopping excess levothyroxine under physician supervision, antithyroid medications (e.g., methimazole or PTU), radioactive iodine ablation, or thyroidectomy for persistent hyperthyroidism. Avoid excess iodine (supplements, seaweed, contrast) and discuss biotin interference with lab tests. Regular monitoring and endocrinology follow-up are essential; don’t change medications without medical advice.