Serum/plasma concentration of free testosterone (immunoassay)

Why This Test Matters

Free testosterone is the biologically active form of testosterone that circulates freely in your blood. Unlike total testosterone, which includes both free and bound forms, free testosterone is directly available to your cells. This test helps doctors evaluate your hormone health, especially in conditions affecting sex hormones, fertility, or symptoms like low libido or irregular menstrual cycles.

What to Expect Before the Test

No special preparation is needed for this test. You may have a blood draw at your doctor’s office or a lab. If you’re taking medications that affect hormones, like certain birth control pills or steroids, let your healthcare provider know before the test.

Common Reasons for Testing

Your doctor might order this test to check for hormonal imbalances, diagnose conditions like hypogonadism (low testosterone) or hyperandrogenism (high testosterone), or monitor treatment for hormone-related disorders. It’s also used in fertility evaluations or to assess symptoms like fatigue, mood changes, or changes in body hair.

What the Results Mean

Results are compared to reference ranges for your age, sex, and health status. While specific ranges vary by lab, low free testosterone may indicate conditions like pituitary disorders or androgen resistance, while very high levels could suggest tumors or other hormonal issues. Your doctor will interpret results in the context of your overall health.