Testosterone
HormonesWhat is Testosterone?
Testosterone is the primary androgenic (male sex) hormone, though it is produced in both men and women. In men, the testes produce approximately 95% of testosterone, with the remainder from the adrenal glands. In women, testosterone is produced in smaller amounts by the ovaries and adrenal glands. Testosterone is essential for the development of male reproductive tissues, muscle mass, bone density, body hair, deepening of the voice during puberty, and sperm production. It also plays important roles in mood, energy, cognitive function, and sexual desire in both sexes.
Most testosterone in the blood is bound to proteins—approximately 60–70% is bound to sex hormone-binding globulin (SHBG) and 30–40% to albumin. Only 1–3% circulates as free (unbound) testosterone, which is the biologically active form. Total testosterone measures all forms combined, while free testosterone measures only the unbound fraction. Testosterone levels follow a circadian rhythm with peak levels in the early morning, and they decline gradually with age—approximately 1–2% per year after age 30 in men. Testing should ideally be performed between 7–10 AM for the most accurate results.
Why It Matters
Testosterone is critical for sexual health, bone strength, muscle mass, mood regulation, and cardiovascular health in both men and women. In men, low testosterone (hypogonadism) affects an estimated 4–5 million Americans and is associated with decreased libido, erectile dysfunction, reduced muscle mass, increased body fat, osteoporosis, depression, and metabolic syndrome. In women, testosterone excess (as in polycystic ovary syndrome) leads to acne, hirsutism, menstrual irregularities, and infertility, while deficiency may contribute to low libido and fatigue. Accurate testosterone measurement is essential for diagnosing and managing these conditions.
Normal Reference Ranges
| Group | Range | Unit |
|---|---|---|
| Adult Men (total) | 270–1070 | ng/dL |
| Adult Women (total) | 15–70 | ng/dL |
| Adult Men (free) | 5–21 | ng/dL |
Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.
What High T Levels Mean
Common Causes
- Polycystic ovary syndrome (PCOS) in women
- Congenital adrenal hyperplasia
- Androgen-secreting tumors (adrenal or ovarian/testicular)
- Exogenous testosterone or anabolic steroid use
- Cushing's syndrome
- Insulin resistance and obesity (can initially raise testosterone in women)
Possible Symptoms
- Acne and oily skin
- Excess facial and body hair growth (hirsutism) in women
- Male-pattern hair loss
- Deepening of the voice in women
- Menstrual irregularities or absent periods in women
- Increased muscle mass
- Aggressive behavior or mood changes
- Infertility
What to do: High testosterone in women should be investigated for PCOS (the most common cause) with pelvic ultrasound, LH/FSH ratio, insulin levels, and DHEA-S. If an androgen-secreting tumor is suspected (rapidly progressive symptoms, very high testosterone), adrenal CT and ovarian ultrasound are warranted. Treatment depends on the cause: PCOS is managed with hormonal contraceptives, spironolactone for hirsutism, and lifestyle modifications. In men, unexpectedly high levels without supplementation should raise suspicion for androgen-producing tumors.
What Low T Levels Mean
Common Causes
- Primary hypogonadism (testicular failure from Klinefelter syndrome, orchitis, trauma, or chemotherapy)
- Secondary hypogonadism (pituitary or hypothalamic dysfunction)
- Age-related decline (late-onset hypogonadism)
- Obesity and metabolic syndrome
- Chronic opioid use
- Chronic illness (HIV, liver cirrhosis, chronic kidney disease)
- Medications (corticosteroids, ketoconazole, spironolactone)
Possible Symptoms
- Decreased libido and sexual desire
- Erectile dysfunction in men
- Fatigue and decreased energy
- Loss of muscle mass and strength
- Increased body fat, particularly abdominal
- Decreased bone density (osteoporosis)
- Depression and irritability
- Difficulty concentrating and poor memory
- Decreased body hair
What to do: Low testosterone should be confirmed with a second early-morning measurement. LH and FSH levels distinguish primary (elevated LH/FSH) from secondary (low or normal LH/FSH) hypogonadism. Prolactin and iron studies should be checked to rule out pituitary adenoma and hemochromatosis. In men with confirmed symptomatic hypogonadism, testosterone replacement therapy (TRT) via injections, gels, or patches may be considered after discussing risks and benefits. Lifestyle modifications including weight loss, exercise, and sleep optimization can also improve testosterone levels naturally.
When Is T Testing Recommended?
- When symptoms of low testosterone are present in men (low libido, erectile dysfunction, fatigue, decreased muscle mass)
- When evaluating signs of androgen excess in women (hirsutism, acne, irregular periods, infertility)
- When monitoring testosterone replacement therapy
- When evaluating delayed or precocious puberty in adolescents
Frequently Asked Questions
Related Biomarkers
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Upload Lab Results →Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.