Free testosterone (serum/plasma)

What Does Free Testosterone Measure?

Free testosterone is the portion of testosterone that is not bound to proteins in your blood. It’s the form that directly affects tissues and organs, including those involved in sex drive, muscle mass, and bone health. Unlike total testosterone, which includes both free and bound forms, free testosterone alone reflects your body’s biologically available hormone levels.

Why Is Free Testosterone Important?

Measuring free testosterone helps doctors assess hormone imbalances that could affect fertility, energy levels, mood, and sexual function. It’s particularly useful when total testosterone results are unclear or when protein levels (like albumin) vary.

When Might You Need This Test?

Your doctor may order a free testosterone test if you have symptoms like low libido, fatigue, irregular menstrual cycles (in women), or unexplained muscle weakness. It’s also used in fertility evaluations, hormone replacement therapy planning, and monitoring conditions like polycystic ovary syndrome (PCOS) or hypogonadism.

How Is the Test Performed?

A blood sample is drawn from a vein, typically in the arm. The serum or plasma is then analyzed using an immunoassay method to measure free testosterone levels accurately.