You got your testosterone tested. The number came back. Now what?
The gap between receiving a testosterone result and understanding what it means is wider than most men realize. A "total testosterone" of 450 ng/dL might be perfectly adequate for one man and functionally low for another — and the difference often comes down to numbers most lab reports bury in the fine print: free testosterone and SHBG.
Total Testosterone: The Headline Number
Total testosterone is what most lab reports feature prominently. It measures everything — the testosterone bound to SHBG (inactive), the testosterone loosely bound to albumin (partially available), and the free testosterone floating unbound (fully active).
Standard reference ranges at most commercial labs:
| Lab | Reference Range | Notes |
|---|---|---|
| Quest Diagnostics | 250–1100 ng/dL | Adult males, LC-MS/MS method |
| LabCorp | 264–916 ng/dL | Adult males, updated 2024 |
| Endocrine Society | 300–1000 ng/dL | Guideline-based normal range |
The problem with these ranges: they're based on population distributions that include men from 18 to 80+. A 28-year-old at 310 ng/dL is technically "within range" but significantly below age-matched norms. The reference range tells you whether your number is statistically normal in the broadest population sense — not whether it's optimal for you at your age.
Free Testosterone: The Number That Matters More
Only about 2–3% of your total testosterone circulates free — unbound to any protein and immediately available for cellular use. This is the fraction that drives the effects you actually feel: energy, libido, muscle protein synthesis, mood regulation.
A man with total T of 600 ng/dL and high SHBG might have less bioavailable testosterone than a man with total T of 400 ng/dL and low SHBG. The total number looks better; the functional reality is worse.
Free T reference ranges:
- Direct measurement: 5–21 ng/dL (varies by assay)
- Calculated free T (Vermeulen equation): more accurate than direct immunoassays
- General guideline: clinicians often consider free T below 5–9 ng/dL as potentially symptomatic, depending on age
SHBG: The Hidden Variable
Sex Hormone Binding Globulin is a protein produced by the liver that grabs testosterone and holds it in an inactive state. SHBG is the gatekeeper between total testosterone and free testosterone.
High SHBG (above ~50–60 nmol/L) means more of your testosterone is locked up. Causes include aging, hyperthyroidism, liver disease, estrogen exposure, and certain medications. Men with high SHBG can have perfectly normal total T but functionally low free T.
Low SHBG (below ~20 nmol/L) means more free testosterone is available — but it also means faster metabolic clearance. Causes include obesity, insulin resistance, hypothyroidism, and some genetic variants. Counterintuitively, very low SHBG isn't always advantageous because the testosterone is cleared quickly.
The SHBG takeaway: A testosterone result without SHBG is an incomplete picture. If your total T is borderline and your SHBG is high, your functional testosterone is almost certainly low. If your total T is borderline and your SHBG is low, you may have adequate free T despite a modest total number.
Bioavailable Testosterone: The Compromise Metric
Bioavailable testosterone combines free T plus albumin-bound T. Because albumin binds testosterone loosely, albumin-bound T is considered "bioavailable" — it can dissociate and enter cells relatively easily.
Some clinicians prefer bioavailable T over free T because it captures a larger and more measurable fraction. Others argue that free T measured by equilibrium dialysis or calculated by the Vermeulen equation is the gold standard. Both are more informative than total T alone.
What "Low" Actually Means Clinically
The Endocrine Society defines hypogonadism as total testosterone below 300 ng/dL on two separate morning measurements, accompanied by symptoms. Both criteria must be met — a number alone doesn't establish a diagnosis, and symptoms alone don't either.
Here's where it gets nuanced:
- Below 200 ng/dL: Almost universally symptomatic. Treatment is clearly indicated after confirming the cause.
- 200–300 ng/dL: Most men are symptomatic. Treatment is guideline-supported if symptoms are present and the measurement is confirmed.
- 300–400 ng/dL: The "gray zone." Some men feel fine here; others have significant symptoms. Free T and SHBG become the deciding factors.
- Above 400 ng/dL: Symptoms attributed to "low T" at this level usually have other causes — sleep apnea, depression, metabolic dysfunction, medication side effects.
The Two-Morning-Draw Rule
Testosterone levels fluctuate significantly by time of day, sleep quality, stress, illness, and recent activity. A single low reading is not diagnostic. The protocol requires two separate morning blood draws (before 10 AM) showing consistently low levels. Men who test at 2 PM after a poor night's sleep and a stressful morning may get artificially low numbers that don't represent their actual hormonal status.
Practical Steps After Getting Your Results
Your Post-Lab Action Plan
- Total T in range, feeling fine: No action needed. Retest in 1–2 years for trending.
- Total T borderline (300–450) with symptoms: Get SHBG and free T measured. If free T is low, the conversation changes.
- Total T below 300, confirmed on two draws: Consult an endocrinologist or experienced men's health clinician. Investigate causes before jumping to treatment.
- Total T normal but high SHBG: Address underlying causes (thyroid, liver, medications) before considering TRT. Weight loss and metabolic improvement can lower SHBG naturally.
The Bottom Line
Three Numbers, Not One
A testosterone lab result is a puzzle with three pieces: total T, free T, and SHBG. Any clinic that prescribes TRT based on total testosterone alone — without checking free T and SHBG — is cutting diagnostic corners. Get all three measured, on two separate mornings, before making any treatment decisions.