What Is Testosterone in a Blood Test?
Testosterone is the primary male sex hormone. It regulates muscle mass, bone density, libido, mood, and red blood cell production.
Normal Ranges (Total Testosterone)
- Adult men: 300–1,000 ng/dL
- Peak: age 18–25
- Decline: ~1–2% per year after 30
- Hypogonadism: below 300 ng/dL with symptoms, confirmed twice
- Women: 15–70 ng/dL
Free vs Total
- Total = bound + free (most commonly measured)
- Free = unbound, biologically active (1–3% of total)
- High SHBG lowers free T even when total T is normal
When and How to Test
- Test in the morning (7–10 AM)
- Fast if possible
- Confirm low with a second morning test
- Check LH and FSH to determine cause
Low Testosterone Causes
- Aging, obesity, chronic disease
- Medications — opioids, steroids
- Pituitary or testicular disorders
- Klinefelter syndrome
High Testosterone Causes
- Anabolic steroid use
- TRT over-replacement
- PCOS (women)
- Tumors (rare)
Source: NLM MedlinePlus, American Association for Clinical Chemistry.
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