Sex hormones
Total testosterone
Total androgen; influenced by SHBG. Always interpret with SHBG and free/bioavailable testosterone.
Sample
Serum, 8–10 AM
Clinical reference range
264 to 916 ng/dL
Adult male
Conv: 264–916 ng/dL
Biology
What it measures
Leydig cell product under LH control. ~44% bound to SHBG, ~54% to albumin (bioavailable), 1–2% free.
Clinical use
Why we order it
Diagnose hypogonadism (two morning values <300 with symptoms); monitor TRT.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Endocrine Society 2018 guideline requires symptoms PLUS two unequivocally low morning testosterone values.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Anabolic steroids
- ↑Androgen-secreting tumors
- ↑PCOS (mild in women)
Causes of LOW
- ↓Primary hypogonadism (high LH/FSH)
- ↓Secondary (low LH/FSH — pituitary/hypothalamic)
- ↓Obesity (low SHBG, low total)
- ↓Opioids
Pitfalls
Pre-analytic & interpretation traps
- !Single low total testosterone is insufficient — repeat morning, paired with LH, FSH, SHBG, prolactin.
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