What is the Origin of Bioavailable Steroid Measurement?

This concept evolved from endocrinology as researchers noted that while total hormone levels might appear normal, symptoms of deficiency or excess persisted. The origin lies in understanding protein binding, particularly by Sex Hormone Binding Globulin (SHBG) and Corticosteroid Binding Globulin (CBG). Measuring the unbound fraction acknowledges the physiological reality that binding affinity dictates biological potency. It moves clinical assessment past simple concentration reporting toward functional availability.

What is the Mechanism of Bioavailable Steroid Measurement?

The mechanism involves laboratory separation techniques designed to isolate or calculate the unbound hormone concentration from the total measured level. This often employs equilibrium dialysis or advanced calculations based on total hormone and binding globulin levels. A reduced bioavailable fraction, even with normal total levels, indicates impaired receptor access and reduced endocrine signaling at the cellular level. This calculation is vital for diagnosing true hormonal insufficiency or excess.

Bioavailable Steroid Measurement ∞ Area

Bioavailable Steroid Measurement

Meaning

Bioavailable Steroid Measurement refers to the precise determination of the fraction of a steroid hormone, such as testosterone or cortisol, that is unbound to plasma proteins and thus free to interact with cellular receptors. Only this unbound fraction exerts direct physiological effects on target tissues. Clinically, total hormone levels can be misleading if transport protein concentrations fluctuate significantly. Therefore, this measurement provides a more accurate index of the hormone activity actually available to the body’s cells.