This Testosterone Free and Total Test is an essential diagnostic tool that provides a comprehensive overview of an individual's testosterone levels by measuring both the total testosterone and the bioavailable, free testosterone in the blood. This test combines the assessments of:
Total Testosterone: Represents the cumulative amount of testosterone in the blood, including testosterone bound to proteins like sex hormone-binding globulin (SHBG) and albumin, as well as the free, unbound testosterone. This gives a broad perspective on the body's testosterone production.
Free Testosterone: Specifically measures the fraction of testosterone that circulates unbound in the bloodstream and is available for immediate biological activity. Free testosterone is crucial for understanding the body's available hormone levels that can directly influence physiological and sexual functions.
By concurrently measuring both these components, the Testosterone Free and Total Test offers a nuanced view that is vital for accurately evaluating hormonal health and diagnosing disorders related to testosterone levels. This dual approach is particularly beneficial because it allows distinguishing between cases where the total testosterone level might be within a normal range, but the bioavailable testosterone is abnormally low or high.
This test is often recommended when symptoms suggest testosterone imbalance, such as changes in libido, energy levels, muscle mass, and bone density. It's also a critical part of evaluating conditions like hypogonadism, androgen deficiency, and in monitoring the effectiveness of testosterone replacement therapy.
Overall, the Testosterone Free and Total Test provides valuable insights that aid in the comprehensive assessment of an individual's androgen status, helping guide treatment decisions and manage symptoms related to testosterone levels more effectively.
Testosterone, like other steroid hormones, is derived from cholesterol with production regulated by a classic negative feedback loop called the hypothalamic-pituitary-gonadal (HPG) axis. When testosterone levels are low, the hypothalamus secretes gonadotropin-releasing hormone (GnRH) to stimulate the anterior pituitary to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH). In men, FSH stimulates spermatogenesis, while LH stimulates testicular production of testosterone.
Testosterone secretion occurs in a circadian pattern with the highest levels occurring at 6 AM and the lowest levels at 6 PM. Testosterone is both an androgen and a prohormone which can be converted into an even more potent androgen, dihydrotestosterone (DHT), as well as an estrogenic hormone, estradiol. In males, testosterone and DHT are responsible for the development of external genitalia and secondary sexual characteristics; in females, the main role of testosterone is as an estrogen precursor (Matsumoto 2008).
Testosterone circulates in the blood as a free, active form (less than 5%); weakly bound to albumin (approximately 30%); or tightly bound to sex hormone binding globulin (SHBG, approximately 65%) (Manni 1985). Free and albumin-bound testosterone readily enter cells, and their levels better reflect the testosterone available for use by the body. Together free testosterone and albumin-bound testosterone are called bioavailable testosterone.
Bioavailable testosterone measurements are appropriate in the evaluation of females and children, as well as in males where the total testosterone levels are in the low-normal range or where abnormal SHBG levels are suspected (Ohl 2006).
Testosterone testing may be used to help evaluate the following conditions:
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