Testosterone Free, Profile II is a laboratory assessment that measures the biologically active fraction of testosterone not bound to sex hormone-binding globulin (SHBG) or albumin, typically calculated or measured via equilibrium dialysis or analog immunoassay methods. Free testosterone represents approximately 1–3% of total circulating testosterone and is considered the physiologically active form available to target tissues. This profile often includes total testosterone alongside calculated or directly measured free testosterone to provide a comprehensive hormonal assessment. Testosterone is primarily produced in the Leydig cells of the testes in males and, to a lesser extent, in the ovaries and adrenal glands in females, under regulation by the hypothalamic-pituitary-gonadal (HPG) axis via luteinizing hormone (LH). In circulation, approximately 44–65% of testosterone is tightly bound to SHBG, 33–54% is loosely bound to albumin, and only 1–3% circulates as free testosterone available for cellular uptake and androgen receptor binding. Free testosterone levels can be disproportionately elevated or reduced relative to total testosterone when SHBG concentrations are altered by conditions such as obesity, liver disease, thyroid dysfunction, or exogenous hormone use.
Free testosterone is the small portion of testosterone in your blood that is not attached to proteins and is immediately available for your body to use. Unlike total testosterone, which includes hormone bound to proteins, free testosterone reflects what your tissues can actually access. Measuring free testosterone is helpful when doctors want to understand whether you have too much or too little active testosterone, especially when protein levels in your blood may be affecting the total testosterone reading. This test is commonly used to evaluate symptoms like low energy, changes in sexual function, irregular periods, or unwanted hair growth. Your doctor will interpret this result alongside other hormone tests and your symptoms to get a complete picture.
When elevated: Elevated free testosterone may indicate androgen excess states, which in women can manifest as hirsutism, acne, menstrual irregularities, virilization, or features consistent with PCOS or androgen-secreting tumors. In men, elevated free testosterone may be associated with exogenous androgen use, anabolic steroid administration, or, rarely, androgen-secreting neoplasms. Elevated levels may also reflect decreased SHBG with normal total testosterone, as seen in obesity, insulin resistance, or hypothyroidism. When low: Low free testosterone in men is associated with symptoms of hypogonadism including decreased libido, erectile dysfunction, fatigue, loss of muscle mass, decreased bone density, and mood disturbances. In women, low free testosterone may contribute to reduced libido, fatigue, and decreased sense of well-being, though clinical thresholds are less well-established. Low free testosterone may result from primary gonadal failure, hypothalamic-pituitary dysfunction, or elevated SHBG reducing the free fraction despite normal total testosterone.
Free testosterone is the hormonally active form driving muscle protein synthesis, recovery, and performance adaptations to training. Athletes monitor this marker to assess anabolic status, training stress, and whether total testosterone levels accurately reflect hormonal availability—particularly useful when SHBG varies due to body composition changes, thyroid function, or training intensity.
Fasting Required
No
Method
Albumin: Colorimetric, Testosterone: Liquid chromatography/tandem mass spectrometry (LC/MS-MS), SHBG: Electrochemiluminescence immunoassay (ECLIA)
verifiedGold StandardMass spectrometry — higher accuracy, especially at low concentrations
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$55.00
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