Total Testosterone
Total T· also: Total Testosterone, TT
Clinical Overview
Testosterone is the primary male sex hormone, produced mainly in the testes in men and in smaller amounts in the ovaries and adrenal glands in women. It is essential for male sexual development, muscle mass, bone density, red blood cell production, and libido. In women, elevated testosterone may indicate PCOS or adrenal disorders.
Why This Test Matters
Low testosterone (hypogonadism) in men is associated with fatigue, reduced libido, erectile dysfunction, loss of muscle mass, osteoporosis, and metabolic syndrome. Two morning total testosterone measurements below the lower limit of normal (typically <300 ng/dL) confirm hypogonadism. In women, elevated total testosterone combined with clinical features (acne, hirsutism, irregular periods) supports a diagnosis of PCOS or adrenal hyperandrogenism.
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Male | 300 – 1000 | ng/dL | — |
| Adults (18–64) | Female | 15 – 70 | ng/dL | — |
Also reported in: nmol/L.
Critical (Panic) Values
Critical Low: < 100 ng/dL. Values outside these limits require immediate clinical attention.
What Causes Abnormal Results?
High Total T Causes
- In men: exogenous testosterone therapy, anabolic steroid use
- In women: PCOS (most common), congenital adrenal hyperplasia, adrenal tumor, ovarian tumor
- Rare: testosterone-secreting tumor
Low Total T Causes
- Primary hypogonadism (testicular failure): Klinefelter syndrome, chemotherapy, radiation, orchitis
- Secondary hypogonadism: pituitary or hypothalamic disease, hyperprolactinemia, obesity
- Aging (testosterone declines ~1–2% per year after age 30)
- Opioid use (suppresses the hypothalamic-pituitary axis)
- Corticosteroid use
- Severe systemic illness
Signs & Symptoms to Watch For
How to Prepare for This Test
Draw between 7–10 AM when testosterone is at its daily peak (circadian rhythm). Fasting is preferred. Two separate morning measurements are required to confirm hypogonadism, as testosterone levels vary day to day.
Factors That Can Affect Results
- Time of day (testosterone is highest in the morning — afternoon values can be 20–30% lower)
- Obesity (adipose tissue converts testosterone to estradiol, lowers testosterone)
- SHBG levels (affect total testosterone without changing free testosterone)
- Acute illness (testosterone drops during acute illness)
- Exogenous testosterone or anabolic steroids (suppress endogenous production)
Related Topics
Frequently Asked Questions
What is the difference between total and free testosterone?
Total testosterone measures all testosterone in the blood — protein-bound (to SHBG and albumin) plus the small free fraction (~2%). Free testosterone is the biologically active portion. When SHBG is elevated (obesity, thyroid disease, aging, liver disease), total testosterone can appear low while free testosterone is adequate. Free testosterone or calculated free testosterone is more accurate for assessing androgen status in these situations.
Should I take testosterone replacement if my level is low?
Testosterone replacement therapy (TRT) is indicated in men with confirmed hypogonadism (two low morning levels) and symptoms. Before starting, the cause should be identified and treatable causes addressed. TRT is contraindicated in men with prostate cancer, elevated hematocrit, untreated sleep apnea, or plans for future fertility (TRT suppresses sperm production). Benefits include improved libido, energy, mood, muscle mass, and bone density.