Before starting TRT, you need two morning total testosterone tests (drawn between 7-10 AM, ideally fasted, on separate days) plus a supporting panel: free testosterone, LH/FSH, estradiol, hematocrit, PSA, and SHBG. Both the AUA and Endocrine Society require two low morning readings — generally below ~300 ng/dL — before diagnosing low testosterone. Here’s what every test means, what the numbers should look like, and how online clinics handle the whole process.
Why Blood Work Matters So Much for TRT#
TRT is one of the few treatments where the diagnosis lives almost entirely in your blood work. Symptoms like fatigue, low libido, and brain fog overlap with dozens of other conditions — poor sleep, depression, thyroid problems, vitamin D deficiency. Blood work is how you and your provider confirm that low testosterone is actually the problem, and later, that treatment is working safely.
Any clinic that offers to prescribe testosterone without blood work is a red flag. Legitimate providers — online or local — always test first.
The Core Panel: Test by Test#
Total Testosterone#
What it measures: All the testosterone in your blood — both bound to proteins and free.
Reference range: Roughly 300-1,000 ng/dL for adult men, though exact ranges vary by lab.
What matters: The AUA defines low testosterone as below 300 ng/dL on two separate morning tests. The Endocrine Society uses a similar threshold and emphasizes confirming with a repeat test, because a single low reading is wrong surprisingly often — up to 30% of men with one low result test normal on repeat.
Total testosterone is the headline number, but it doesn’t tell the whole story. That’s where the next test comes in.
Free Testosterone#
What it measures: The 1-3% of testosterone that isn’t bound to proteins — the fraction your body can actually use.
Reference range: Approximately 5-21 ng/dL (or 50-210 pg/mL, depending on the lab’s units and method).
Why it matters: Two men with identical total testosterone can feel completely different if one has much higher SHBG (see below) binding up his testosterone. If your total T is borderline but your free T is clearly low — and you have symptoms — that’s meaningful. Guidelines recommend checking free T specifically when total T is near the cutoff.
LH and FSH (Luteinizing Hormone and Follicle-Stimulating Hormone)#
What they measure: The pituitary signals that tell your testes to produce testosterone (LH) and sperm (FSH).
Why they matter: These two tests answer a critical question — where is the problem?
- High LH + low testosterone = primary hypogonadism. Your brain is shouting, but your testes aren’t responding. TRT is usually the appropriate treatment.
- Low or normal LH + low testosterone = secondary hypogonadism. The signal itself is weak. This can be caused by weight gain, chronic stress, sleep deprivation, certain medications, or (rarely) a pituitary issue. Sometimes this pattern responds to lifestyle changes or fertility-preserving medications like clomiphene instead of TRT — which matters a lot if you want kids. Read more in our TRT and fertility guide.
Estradiol (E2)#
What it measures: Your primary estrogen. Yes, men need estrogen — it’s made from testosterone via the aromatase enzyme and supports bone density, joint health, libido, and mood.
Reference range: Roughly 10-40 pg/mL on a sensitive (LC/MS) assay. Ask for the sensitive assay — the standard assay was designed for women and is unreliable at male levels.
Why it matters on TRT: When testosterone goes up, estradiol usually goes up too. Most men feel fine with moderately elevated E2, but very high levels can cause water retention, moodiness, or nipple sensitivity. Providers generally treat symptoms, not numbers — reflexively prescribing anastrozole for a slightly high E2 with no symptoms is an outdated practice.
Hematocrit (via Complete Blood Count)#
What it measures: The percentage of your blood made up of red blood cells.
Reference range: Roughly 38-50% for men.
Why it’s the most important safety marker on TRT: Testosterone stimulates red blood cell production. If hematocrit climbs too high (above 54%, per Endocrine Society guidance), blood becomes thicker and the theoretical risk of clots rises. This is the single most common reason for dose adjustments on TRT. Management options include lowering the dose, switching from injections to a transdermal, splitting injections into smaller more frequent doses, or therapeutic blood donation.
PSA (Prostate-Specific Antigen)#
Who needs it: Generally men 40 and older before starting TRT, per AUA guidance (some providers start at 45-50 for average-risk men).
Why it matters: Current evidence does not show that TRT causes prostate cancer, but testosterone can accelerate the growth of an existing cancer. A baseline PSA screens for undiagnosed prostate issues before you start, and periodic monitoring catches significant changes. A PSA increase of more than 1.4 ng/mL in a year, or a confirmed level above 4.0, warrants urology referral.
SHBG (Sex Hormone-Binding Globulin)#
What it measures: The protein that binds most of your testosterone and controls how much is free.
Why it matters: SHBG rises with age and certain conditions (liver issues, hyperthyroidism) and falls with obesity, insulin resistance, and diabetes. High SHBG can make a “normal” total testosterone functionally low; low SHBG can do the opposite. SHBG context is essential for interpreting borderline results.
Supporting Tests Worth Getting#
- Comprehensive metabolic panel (CMP) — liver and kidney function, blood glucose
- Lipid panel — baseline cholesterol, since TRT can modestly affect lipids
- Prolactin — if LH is low, to rule out a pituitary cause
- Thyroid (TSH) — hypothyroid symptoms mimic low T almost exactly
- Vitamin D and B12 — common deficiency causes of fatigue
When and How to Test: Getting Accurate Numbers#
The three rules for an accurate testosterone test:
- Test in the morning (7-10 AM). Testosterone peaks in the early morning and can drop 20-30% by afternoon. Diagnostic cutoffs are based on morning values.
- Test fasted. Eating — especially glucose — can transiently lower testosterone. An overnight fast with a morning draw is standard.
- Test twice. One low reading isn’t a diagnosis. Illness, poor sleep the night before, or normal biological variation can tank a single result. Both AUA and Endocrine Society guidelines require two separate low morning tests before diagnosing hypogonadism.
Other things that skew results: acute illness, a night of heavy drinking, severe sleep deprivation, recent intense training, and crash dieting. If any of these apply, wait a week or two and test then.
Curious how your numbers compare to other men your age? Use our testosterone levels by age tool to see where you fall.
What Do the Results Mean? Quick Interpretation Guide#
| Pattern | Likely Meaning | Typical Next Step |
|---|---|---|
| Total T <300, high LH | Primary hypogonadism | TRT candidate |
| Total T <300, low/normal LH | Secondary hypogonadism | Investigate cause; TRT or alternatives |
| Total T 300-400 with symptoms | Borderline | Check free T, SHBG; retest |
| Total T normal, free T low, high SHBG | Functionally low | Treat based on symptoms + free T |
| Total T normal, symptoms present | Look elsewhere | Thyroid, sleep, vitamin D, mental health |
If your levels are borderline and you’re not sure whether your symptoms fit, our low testosterone symptoms guide walks through what low T actually feels like at different severities.
How Online TRT Clinics Handle Blood Work#
One of the most common questions about telehealth TRT: how do they test my blood over the internet? They don’t — they coordinate real lab draws. The typical process:
- You complete an intake questionnaire about symptoms and health history
- The clinic sends a lab order to a national chain like Quest Diagnostics or LabCorp
- You walk into a local draw site (usually a 10-15 minute visit, morning appointment)
- Results go directly to the clinic’s physicians, who review them with you in a telehealth consult
- If you qualify, medication ships to your door; if not, a good clinic tells you so
Some clinics include the initial panel in their price; others charge $100-300 separately. A few offer at-home fingerstick collection kits — convenient, but venous draws are more accurate and are what guidelines are based on, so most quality clinics use walk-in labs for diagnosis. See the full step-by-step in how online TRT works.
Follow-up schedule to expect: repeat labs at 6-12 weeks after starting (to check your levels on your dose, plus hematocrit and estradiol), then every 6-12 months once stable. A clinic that never asks for follow-up labs is not monitoring you properly.
Key Takeaways#
- Two morning, fasted total testosterone tests are required for a proper diagnosis — below ~300 ng/dL is the guideline cutoff
- Free T, SHBG, and LH/FSH turn a single number into an actual diagnosis
- Hematocrit is the most important ongoing safety marker — keep it under 54%
- PSA at baseline for men 40+, monitored periodically on treatment
- Online clinics use real labs (Quest/LabCorp) — no legitimate provider skips blood work
- Retest at 6-12 weeks, then every 6-12 months once your protocol is stable
Ready to Get Tested?#
Both of our recommended clinics coordinate comprehensive lab panels and have physicians review your results before any prescription is written.
See our recommended TRT clinics →
What does TRT cost, labs included? →
This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare provider before starting any treatment. Affiliate disclosure