Hormone Panel Basics: Testosterone, Estradiol, SHBG, LH and FSH
A hormone panel is only as useful as the conditions it was drawn under. Here is what each common marker measures, how timing and method change the numbers, and how to convert between US and SI units.
The markers
| Marker | What it tells you |
|---|---|
| Total testosterone | All testosterone in the blood, bound and unbound. |
| SHBG | Sex hormone-binding globulin, the protein that binds testosterone tightly. High SHBG means less of the total is available. |
| Free testosterone | The small unbound fraction. Usually calculated from total testosterone, SHBG and albumin, or measured by equilibrium dialysis. |
| Estradiol (E2) | The main estrogen. In men and postmenopausal women, levels are low enough that a sensitive LC/MS-MS assay is more accurate than standard immunoassays. |
| LH and FSH | Pituitary hormones that signal the testes or ovaries. External androgens suppress them. |
| Prolactin | Pituitary hormone; high levels can suppress testosterone and libido. |
Timing matters
- Men: testosterone peaks in the morning, so draw between about 7 and 10 AM, fasted. Endocrine guidelines call for two separate morning results before concluding testosterone is low, because single values vary.
- Women: estradiol, progesterone, LH and FSH change across the menstrual cycle. Baseline hormones are usually drawn in the early follicular phase (cycle days 2-5); progesterone to confirm ovulation is drawn about a week after it.
- Recent illness, poor sleep and very low calorie intake all lower testosterone temporarily.
Unit conversions
| Marker | US unit | SI unit | Conversion |
|---|---|---|---|
| Testosterone | ng/dL | nmol/L | ng/dL × 0.0347 = nmol/L |
| Free testosterone | pg/mL | pmol/L | pg/mL × 3.47 = pmol/L |
| Estradiol | pg/mL | pmol/L | pg/mL × 3.671 = pmol/L |
Compounds that act on this axis, such as Kisspeptin-10, Gonadorelin and hCG, are studied by tracking exactly these markers.
This guide explains lab tests. It is not medical advice, does not interpret individual results, and does not endorse using any compound. Review your results with a licensed clinician.
FAQ
What time should testosterone be tested?
In the morning, roughly 7 to 10 AM, after fasting, because testosterone peaks early in the day. Guidelines recommend confirming a low result with a second morning test.
What is the difference between total and free testosterone?
Total testosterone includes hormone bound to SHBG and albumin plus the small unbound fraction. Free testosterone is only the unbound part, usually calculated from total testosterone, SHBG and albumin.
Why use a sensitive estradiol test?
Standard estradiol immunoassays are designed for the higher levels seen in premenopausal women and can be inaccurate at the low levels typical in men. LC/MS-MS sensitive assays measure low values more reliably.