What is the Origin of Total and Free Hormones?

This terminology is fundamental to clinical endocrinology, distinguishing between the reservoir and the active component of steroid and thyroid hormones. It arose from the discovery of plasma binding proteins like sex hormone-binding globulin (SHBG). Measuring both fractions provides a more complete picture of endocrine function.

What is the Mechanism of Total and Free Hormones?

The vast majority of hormones are bound to carrier proteins, which serve as a circulating reservoir and protect the hormone from rapid metabolic clearance. The free fraction is the key mechanistic component, as only these unbound molecules can pass through cell membranes to activate intracellular receptors. Measuring both total and free levels provides a complete picture of production and bioavailability.

Total and Free Hormones

Meaning

Total and Free Hormones are two distinct yet related measures of hormone concentration in the bloodstream: “Total Hormones” represent the sum of all circulating hormone molecules, both those bound to transport proteins and those unbound. “Free Hormones” are the small fraction of unbound molecules that are biologically active and capable of diffusing into tissues to exert their effect. The free fraction is generally considered the more accurate reflection of a patient’s true hormonal status.