Low testosterone in men: the lab panel and what the numbers really mean
Anchor biomarkers: Total testosterone, free testosterone, SHBG, LH, FSH
TL;DR
- •Total testosterone is just the start. The pattern across total T + free T + SHBG + LH + FSH tells you *where* the problem is — the testes or the brain's signal.
- •"Low normal" total T with low SHBG can still be symptomatic. And "in range" total T with high SHBG can still be functionally low.
- •Testosterone replacement is not a one-way street. Before reaching for treatment, the panel often reveals reversible drivers (sleep, weight, insulin resistance, opioid use, certain medications).
What each marker tells you
| Marker | Reference range | What it means |
|---|---|---|
| Total testosterone | 264 – 916 ng/dL (varies by lab) | The total circulating pool. Most labs flag < 300 as low; many practitioners use < 400 as functional concern. |
| Free testosterone | 5 – 21 ng/dL (varies; lab-dependent) | The bioavailable fraction reaching tissues. The number that correlates best with symptoms. |
| SHBG | 10 – 57 nmol/L | Binds testosterone. High SHBG = less free T despite normal total. Low SHBG = more free T despite low-normal total. |
| LH (luteinizing hormone) | 1.5 – 9.3 mIU/mL | The brain's signal to the testes. Elevated = testes underperforming despite the brain shouting (primary hypogonadism). Normal-or-low with low T = brain not signaling enough (secondary hypogonadism). |
| FSH (follicle stimulating hormone) | 1.4 – 18.1 mIU/mL | Brain signal for sperm production. Pattern across LH + FSH localizes the problem. |
| Estradiol | 8 – 60 pg/mL (sensitive assay) | Testosterone converts to estradiol via aromatase. Excess body fat → more aromatase → more estradiol → suppression of T. |
| Prolactin | < 18 ng/mL | High prolactin (pituitary issue) suppresses GnRH → low LH/FSH → low T. Always check before diagnosing "idiopathic" low T. |
| TSH + free T4 | normal | Thyroid dysfunction can mimic low-T symptoms. |
| HbA1c, fasting insulin | normal | Metabolic dysfunction is a common, reversible driver of low T. |
| Hematocrit | 38.8 – 50.0% | Tracked on testosterone therapy — TRT often raises hematocrit. |
| PSA | < 4 ng/mL (age-dependent) | Baseline before any testosterone therapy. |
Three real patterns Phi has seen
Example patterns · synthetic data drawn from Phi's scenario library. Not real patient records.
Pattern 1 — Secondary hypogonadism driven by metabolic dysfunction.
Total T 285 (low). Free T 6.2 (low). SHBG 15 (low). LH 3.2 (low-normal). FSH 4.1 (low-normal). Estradiol 38 (high-normal). Fasting insulin 22. HbA1c 6.1. BMI 32. The patient is told "your T is low, do you want TRT?" The Phi read: this is *secondary* hypogonadism (the brain isn't signaling because insulin resistance and adiposity are suppressing the HPG axis). The right first move is metabolic intervention — weight loss, sleep, exercise — which often raises T 100–200 points without medication. TRT becomes a fallback, not a first-line.
Example pattern · synthetic data
Pattern 2 — Primary hypogonadism with elevated gonadotropins.
Total T 240 (low). Free T 5.1 (low). SHBG 38. **LH 18 (elevated)**. **FSH 22 (elevated)**. Estradiol 24. Normal metabolic panel. The pattern: testes failing despite the brain shouting (high LH/FSH). Causes include prior chemotherapy, undescended testicles, prior infections, autoimmune, or aging. Lifestyle changes won't restore T meaningfully — TRT or, if fertility is a goal, hCG-based protocols may be appropriate. Different clinical pathway entirely than Pattern 1.
Example pattern · synthetic data
Pattern 3 — "Total T normal, free T low, symptomatic."
Total T 425 (normal). Free T 4.8 (low). SHBG 78 (elevated). LH 6.1. FSH 7. Estradiol 32. The standard reading: "Your testosterone is fine." The Phi read: high SHBG is binding the testosterone, leaving little free fraction available at tissue receptors. The patient is symptomatic for a reason. Common drivers of high SHBG: hyperthyroidism, aging, low body fat, certain medications, and liver issues. Addressing the SHBG driver often restores free T without changing total T.
Example pattern · synthetic data
Questions to bring to your doctor
- Have we measured free testosterone and SHBG — not just total?
- What are my LH and FSH telling us about whether the problem is in my testes or the signal from my brain?
- Have we checked prolactin? It's a treatable cause of low T that's often missed.
- What's my metabolic picture — fasting insulin, HbA1c, weight — and could those be driving the T number?
- Is my testosterone trajectory falling year over year, or is it stable?
- Before starting TRT, have we exhausted reversible causes (sleep, weight, medications, opioids, thyroid)?
- If I do start TRT, what's the monitoring plan — hematocrit, PSA, estradiol, lipids, fertility considerations?
What Phi adds beyond a single number
A single "low testosterone" number is a starting point, not a diagnosis. Phi reads the full panel — total T + free T + SHBG + LH + FSH + estradiol + prolactin + metabolic markers — together, and traces the trajectory across the panels you've uploaded. The integrated picture distinguishes primary from secondary hypogonadism, surfaces reversible causes before reaching for TRT, and tracks whether interventions (medical or lifestyle) are actually moving the right markers.
Upload your most recent lab report. Phi will pull out every testosterone-relevant marker, compare them against optimal (not just reference) ranges, flag the pattern, and tell you what to ask at your next appointment.
Frequently asked questions
At what age does testosterone normally decline?
Total T declines roughly 1% per year after age 30 on average. Free T declines faster because SHBG rises with age. Some men never become symptomatic; others become symptomatic well before they cross "low T" thresholds. Symptoms matter more than the number alone.
What are the actual symptoms of low T?
Fatigue (not just tiredness — a sustained low energy), decreased libido, erectile changes, reduced morning erections, mood changes (apathy more than depression), reduced muscle mass despite training, increased body fat (especially abdominal), and sleep disruption. Many of these overlap with metabolic, thyroid, and sleep disorders — so labs matter.
Will TRT shrink my testicles and make me infertile?
TRT shuts down endogenous testosterone production. Testes shrink, sperm production drops, and many men on TRT become infertile within months. Fertility-preserving protocols (clomiphene, hCG, enclomiphene) preserve testicular function and can be alternatives or additions for men who want to maintain fertility.
Should I get TRT from a "low T clinic"?
Quality varies dramatically. The right TRT protocol involves baseline metabolic and prostate evaluation, regular hematocrit and PSA monitoring, careful estradiol management, and consideration of fertility goals. A good endocrinologist or men's health specialist is preferable to clinics that issue testosterone without comprehensive workup.
Can I raise testosterone naturally?
Yes, often significantly — especially for secondary hypogonadism driven by metabolic factors. Weight loss (especially abdominal), resistance training, sleep ≥ 7 hours, addressing sleep apnea if present, vitamin D sufficiency, reducing alcohol, and managing chronic stress all measurably move T in men where the suppression is reversible.
What's a "good" total testosterone for a healthy adult male?
Many longevity-oriented practitioners target the upper half of the reference range (roughly 500–900 ng/dL) when symptomatic and clinically appropriate. The reference range floor (264 in many labs) is based on the lower 2.5% of a population that included many metabolically unhealthy men. "In range" and "optimal" are different conversations.
Is testosterone the same as anabolic steroids?
Testosterone is one anabolic steroid. The doses used in TRT (typically restoring physiologic levels) are very different from the supraphysiologic doses used in athletic doping. The risks scale with dose. Properly monitored TRT is a legitimate medical therapy with well-characterized risk-benefit data.
References
All citations verified against PubMed / publisher of record 2026-05-25.
- 1.Bhasin S, Brito JP, Cunningham GR, Hayes FJ, Hodis HN, Matsumoto AM, Snyder PJ, Swerdloff RS, Wu FC, Yialamas MA. (2018). Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 103(5):1715-1744. — Current standard for diagnosis and management of male hypogonadism: 264 ng/dL CDC-harmonized lower limit, two-morning-draw confirmation, free T via equilibrium dialysis or Vermeulen formula, primary vs secondary hypogonadism, monitoring on TRT. Basis for almost all biomarker thresholds and workup framing.PubMed →DOI →
- 2.Snyder PJ, Bhasin S, Cunningham GR, et al. (Testosterone Trials Investigators). (2016). Effects of Testosterone Treatment in Older Men. New England Journal of Medicine. 374(7):611-624. — The T-Trials: 790 men ≥65 with serum T < 275 ng/dL randomized to testosterone gel vs placebo for 1 year. Sexual function, walking distance, and mood showed improvement; no excess prostate or cardiac events at one year.PubMed →DOI →
- 3.Lincoff AM, Bhasin S, Flevaris P, et al. (TRAVERSE Study Investigators). (2023). Cardiovascular Safety of Testosterone-Replacement Therapy. New England Journal of Medicine. 389(2):107-117. — TRAVERSE: 5,246 men aged 45–80 with hypogonadism and elevated CV risk randomized to testosterone gel vs placebo. TRT was non-inferior to placebo for major adverse cardiovascular events. Basis for the modern view that monitored TRT has acceptable CV-safety profile in appropriately selected patients.PubMed →DOI →
- 4.Vermeulen A, Verdonck L, Kaufman JM. (1999). A critical evaluation of simple methods for the estimation of free testosterone in serum. Journal of Clinical Endocrinology & Metabolism. 84(10):3666-3672. — The Vermeulen formula for calculating free T from total T + SHBG + albumin; basis for the "total T can mislead — SHBG is the missing piece" framing.PubMed →DOI →
Reference ranges for free T vary by laboratory and assay methodology; the Endocrine Society guideline recommends equilibrium dialysis or Vermeulen-formula calculation over older analog "direct" free T assays. The "potentially reversible causes of secondary hypogonadism" list (sleep apnea, obesity, opioids, hyperprolactinemia, vitamin D deficiency, chronic kidney disease, etc.) is detailed in Table 1 of Bhasin et al. 2018. Every link above opens the PubMed abstract or publisher's DOI landing page in a new tab. All citations verified vs PubMed / publisher of record 2026-05-26.
By Steve Pinedo
Co-founder, Phi Longevity
Last updated: 2026-05-26
Steve Pinedo is the Co-founder of Phi Longevity, the AI application that turns a confusing stack of lab reports, wearable data, and clinical notes into a single, integrated picture of your health. He started Phi Longevity to make proactive health and wellness far easier to achieve. He realized how difficult it was for clients to manage their own care, records and coordination so he assembled a comprehensive M.D. led clinical team behind the platform, packaging the proactive-care experience that delivered measurable outcomes (lower triglycerides, reduced body fat, improved LDL, balanced hormones, relief from long-running autoimmune conditions) for any patient with a complicated lab to use now with an application. More about Phi →