How to Read Your Testosterone Lab Results

You got your testosterone tested. The results came back. Your doctor says "everything looks normal." But something still feels off — low energy, brain fog, declining libido, a body that doesn't respond to training the way it used to. Sound familiar?

The problem is that "normal" and "optimal" are very different things when it comes to testosterone. This guide teaches you how to read your own results, understand what each marker actually tells you, and recognize when "normal" is actually suboptimal.

The Key Markers (And What They Mean)

Total Testosterone

What it is: The total amount of testosterone in your blood — both free (bioavailable) and bound (to SHBG and albumin). This is the "headline number" most men focus on.

Lab reference range: 264-916 ng/dL (this varies by lab)
Optimal: 600-900 ng/dL for most men 25-55

Common mistake: A man with total T of 350 ng/dL is told he's "normal." Technically true — 350 falls within the lab reference range. But that reference range is built from a population that includes obese, sedentary, and metabolically unhealthy men. For an active 35-year-old, 350 is likely symptomatic.

Free Testosterone

What it is: The testosterone that's actually available for your body to use. Only 2-3% of total testosterone is "free" — the rest is bound to proteins (primarily SHBG). This is arguably the more important number.

Lab reference range: 5-21 ng/dL
Optimal: 15-25 ng/dL

Why it matters: You can have a total T of 700 ng/dL (looks great on paper) but if your SHBG is extremely high, your free T could be 8 ng/dL — functionally low. Free T tells you what your tissues are actually seeing.

Testing note: Request "direct free testosterone" (equilibrium dialysis or ultrafiltration) rather than calculated free T. The calculated version uses algorithms that can be inaccurate, especially at extremes of SHBG.

SHBG (Sex Hormone Binding Globulin)

What it is: A protein produced by your liver that binds to testosterone. Higher SHBG = more testosterone bound up = less free testosterone available.

Lab reference range: 10-57 nmol/L
Optimal: 20-40 nmol/L

What drives it up: Hyperthyroidism, low-carb/keto diets, aging, liver issues, certain medications
What drives it down: Obesity, insulin resistance, type 2 diabetes, high-dose androgens

Estradiol (E2) — Sensitive Assay

What it is: The primary estrogen in men. Men need estrogen — it's essential for bone health, brain function, cardiovascular protection, and libido. The goal isn't to eliminate estrogen; it's to keep it balanced with testosterone.

Lab reference range: 8-35 pg/mL
Optimal: 20-30 pg/mL

Critical note: Always request the sensitive estradiol assay (LC/MS method). The standard immunoassay is designed for detecting female-range estrogen levels and is unreliable at the lower levels found in men. Many labs default to the standard assay — you must specify sensitive.

LH and FSH: The Upstream Signals

LH (Luteinizing Hormone) and FSH (Follicle-Stimulating Hormone) are produced by the pituitary gland. LH signals your testes to produce testosterone. FSH stimulates sperm production. These are critical for understanding why testosterone is low.

• Low T + High LH/FSH: Primary hypogonadism — the testes aren't responding to the pituitary signal. The brain is sending the message, but the testes can't produce enough testosterone.
• Low T + Low LH/FSH: Secondary hypogonadism — the pituitary isn't sending enough signal. Could indicate a pituitary issue, obesity-driven suppression, or medications affecting the HPG axis.
• Low T + Low LH (on TRT): Expected and normal — exogenous testosterone suppresses pituitary LH production via negative feedback.

Prolactin: The Hidden Disruptor

If testosterone is genuinely low and LH/FSH are also low, prolactin should be tested. Elevated prolactin (from medications, pituitary adenomas, or other causes) suppresses GnRH → LH → testosterone production. It's an often-overlooked cause of secondary hypogonadism.

Normal range: 4-15 ng/mL for men
Red flag: Prolactin above 20 ng/mL warrants investigation. Above 50 suggests possible pituitary adenoma — MRI is recommended.