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)