Thyroid Check

This panel looks at thyroid function from several complementary angles, which matters because thyroid health is not captured by a single number. The thyroid gland produces hormones that regulate metabolic rate, body temperature, heart function, lipid metabolism, and brain activity. These hormones influence nearly every organ system, making even mild dysfunction relevant for long term healthspan and cardiovascular risk.

Thyroid stimulating hormone, or TSH, is released by the pituitary gland in response to signals from the hypothalamus. Its job is to tell the thyroid how much hormone to produce. This feedback loop is called the hypothalamic pituitary thyroid axis. When circulating thyroid hormone levels rise, TSH is suppressed. When hormone levels fall, TSH increases. Because of this tight feedback, TSH is very sensitive to small changes in thyroid function.

That said, TSH reflects pituitary signaling, not hormone action in tissues, and it can appear normal in certain conditions such as central hypothyroidism, where the pituitary itself is not responding appropriately.

Free T4 and free T3 measure the unbound fractions of thyroxine and triiodothyronine that are biologically active. Most thyroid hormone in blood is bound to transport proteins and unavailable to cells. The free fraction is what enters tissues and drives metabolic effects.

T4 is the main hormone produced by the thyroid, while T3 is the more active form that binds thyroid hormone receptors. Much of T3 is produced outside the thyroid by conversion from T4 in organs like the liver, kidney, muscle, and brain. Low free T4 or free T3 can explain symptoms even when TSH is only mildly abnormal, and discordance between these values can point to impaired hormone conversion or altered binding.

Total T4 and total T3 measure both bound and unbound hormone. These values are influenced by thyroid binding proteins, which can change with estrogen status, pregnancy, liver disease, and certain medications. Total hormone levels help distinguish true thyroid dysfunction from changes driven by altered binding proteins.

For example, total T4 may appear high when binding proteins are elevated, even though free T4 and thyroid function are normal. Looking at both free and total hormones adds context and prevents misinterpretation.

Thyroid peroxidase antibodies, often called TPO antibodies, assess autoimmune activity against the thyroid. Thyroid peroxidase is an enzyme required for thyroid hormone synthesis. When the immune system produces antibodies against this enzyme, it can gradually damage thyroid tissue.

This process underlies Hashimoto thyroiditis, the most common cause of hypothyroidism in adults. TPO antibodies can be present years before TSH or hormone levels become abnormal, making them an early warning signal for future thyroid failure. Their presence also explains why thyroid levels may fluctuate over time rather than follow a linear decline.

Taken together, this panel allows you to see regulation at the brain level, hormone availability in circulation, downstream conversion to active hormone, and immune mediated risk. This is especially useful for people focused on longevity, since subtle thyroid dysfunction can influence lipid levels, insulin sensitivity, heart rhythm, bone health, and cognitive function long before overt disease is diagnosed.