t4 free direct dialysis

Free T4, or thyroxine, is the active thyroid hormone that regulates metabolism, energy, and body temperature. This test measures the unbound form of T4 circulating in your blood—the portion your body can actually use. Low free T4 suggests an underactive thyroid (hypothyroidism), causing fatigue and weight gain. High free T4 indicates an overactive thyroid (hyperthyroidism), causing rapid heartbeat and anxiety. Free T4 is often ordered alongside TSH to assess thyroid function comprehensively.

The free T4 index is a calculated measure of thyroid hormone activity that estimates the amount of thyroxine (T4) available to affect your metabolism. Unlike total T4, it accounts for proteins that bind thyroid hormones, providing a more accurate picture of active thyroid hormone. This test helps evaluate thyroid function and diagnose hyperthyroidism or hypothyroidism when TSH alone may be unclear.

This panel measures both thyroid stimulating hormone (TSH) from the pituitary gland and free T4 (thyroxine), the active thyroid hormone. Together, these tests provide a comprehensive assessment of thyroid function. TSH shows whether the pituitary is signaling the thyroid correctly, while free T4 measures the actual active hormone. This combination is more reliable than either test alone for diagnosing thyroid disorders.