A hormone blood panel provides a snapshot of the endocrine system at one moment in time. Single values are less meaningful than patterns across multiple tests, and no single number tells the whole story without context from the others. This guide explains what each commonly measured hormone means, what causes it to be high or low, and how the values interrelate.

Testosterone (Total)

What it measures: Total testosterone includes bound and free fractions. Most testosterone circulates bound to SHBG (inactive) or albumin (loosely bound, biologically available). Free testosterone, the unbound fraction, is approximately 2-3% of the total.

Normal range: 300-1,000 ng/dL in adult men. Laboratory reference ranges vary slightly. The bottom of the range (below 300 ng/dL) with symptoms meets the biochemical criterion for hypogonadism per Endocrine Society guidelines.

Timing matters: Testosterone peaks between 7-10 am and falls throughout the day by 20-40%. All testosterone measurements for diagnostic purposes should be collected between 7-10 am. An afternoon testosterone test that comes back low may reflect the diurnal decline, not true hypogonadism.

Two samples required: A single low value should be confirmed with a second morning sample on a separate day before concluding deficiency.

Free Testosterone

What it measures: The unbound fraction of testosterone available to enter cells and bind androgen receptors.

Normal range: Approximately 9-30 ng/dL (varies by lab and measurement method).

Why it matters: A man with normal total testosterone but high SHBG may have low free testosterone and experience symptoms of deficiency. Conversely, low total testosterone with low SHBG may still provide adequate free testosterone.

Measurement accuracy: Equilibrium dialysis (direct measurement) is the most accurate method. Many labs report “free testosterone” calculated from total testosterone and SHBG using the Vermeulen formula, this is adequate for clinical use but less precise than direct measurement at low levels.

SHBG (Sex Hormone-Binding Globulin)

What it measures: The binding protein that holds most circulating testosterone in an inactive form.

Normal range: Approximately 10-57 nmol/L in adult men, rising with age.

High SHBG: Increases with age, thyroid disease (especially hyperthyroidism), liver disease, and certain medications. High SHBG reduces free testosterone even when total testosterone appears normal.

Low SHBG: Associated with obesity, insulin resistance, type 2 diabetes, and hypothyroidism. Low SHBG may produce higher free testosterone relative to total testosterone.

LH (Luteinizing Hormone)

What it measures: The pituitary hormone that signals the testes to produce testosterone.

Normal range: 1.7-8.6 IU/L (varies by lab).

High LH with low testosterone = primary hypogonadism. The pituitary is working overtime trying to stimulate unresponsive testes.

Low or normal LH with low testosterone = secondary hypogonadism (or tertiary hypogonadism at the hypothalamic level). The pituitary is not sending adequate signal.

LH on TRT: Exogenous testosterone suppresses LH to near-zero. If you are on testosterone replacement, your LH will be undetectable, this is expected and does not reflect a problem.

FSH (Follicle-Stimulating Hormone)

What it measures: The pituitary hormone that drives sperm production (spermatogenesis) in the Sertoli cells.

Normal range: 1.5-12.4 IU/L.

Elevated FSH: Often seen with primary gonadal failure, particularly damage to the seminiferous tubules. Very high FSH with azoospermia (no sperm) indicates non-obstructive azoospermia, a testicular production problem rather than a blockage.

Why FSH matters alongside LH: Together, they help localize where the HPG axis is failing. Both high → primary gonadal failure. Both low or normal with low testosterone → central (hypothalamic or pituitary) failure.

Estradiol (E2)

What it measures: The primary biologically active estrogen in men, produced by aromatization of testosterone.

Normal range: 10-40 pg/mL in men, though this varies by assay type. LC-MS/MS measurement is more accurate at low levels than immunoassay.

High estradiol in men: Associated with obesity (high aromatase in fat tissue), elevated testosterone from TRT, or liver disease. May cause gynecomastia, water retention, reduced libido, and mood changes.

Low estradiol in men: Associated with aromatase inhibitor use, very low testosterone, or aromatase enzyme variants. Causes bone loss, joint pain, and reduced libido.

Prolactin

What it measures: A pituitary hormone that normally rises in women during lactation. In men, elevated prolactin suppresses GnRH and testosterone.

Normal range: Under 20 ng/mL in men (varies by lab).

Elevated prolactin: Causes secondary hypogonadism. Common causes: pituitary prolactinoma (benign tumor), certain medications (antipsychotics, some antidepressants, antiemetics), hypothyroidism, and renal failure.

Why it matters in the hypogonadism workup: A man with low testosterone, low LH, and elevated prolactin likely has a pituitary prolactinoma, a diagnosis requiring MRI and a different treatment approach than TRT.

Putting It Together: Reading the Panel as a Whole

A finding of low testosterone means very different things depending on what the rest of the panel shows:

  • Low T + high LH + high FSH = primary hypogonadism (testicular failure)
  • Low T + low LH + low FSH = secondary hypogonadism (central failure), next step: check prolactin, consider MRI
  • Low T + high prolactin + low LH = prolactinoma until proven otherwise
  • Low T + normal LH + normal FSH + high SHBG = technically adequate LH signaling, but free testosterone may be low due to SHBG binding

For context on what testosterone ranges mean at different ages, see Testosterone Levels by Age: What the Numbers Actually Mean. For the clinical criteria that determine when low testosterone warrants treatment, see What Is Hypogonadism? Primary vs. Secondary Explained.