Bloodwork & Diagnosis
Most men get their blood test back, glance at the column marked "Reference Range," see "normal" written next to each marker, and walk away with no clearer picture than before they paid for the test.
That is not the lab's fault. Reference ranges in the UK and US are built from population averages — the middle 95% of men who walked into a lab. The man who shows up at a GP surgery to ask for a hormone panel is usually not feeling great, which means the "normal" he is being compared to includes a lot of other men who also are not feeling great. The bar is low. The information that matters most — your free testosterone, your SHBG, the relationship between them — is often missing from the panel entirely, or buried in a way that lets a "normal" total testosterone hide a real androgen deficiency.
This article will not give you medical advice. It will give you the framework a sceptical, informed patient uses to read his own results before walking into the consultation. Take it with you. Compare your numbers to it. Then have a real conversation with your doctor armed with something more useful than a smiley face icon.
A lab reference range is a statistical band, not a clinical target. It typically covers the middle 95% of the male population tested at that lab. If 100 men walk in, the lab range will include the two-and-a-half lowest and the two-and-a-half highest as "out of range," and label everyone else "normal."
That works for some markers. A vitamin B12 level of 220 pg/mL is genuinely worse than 600 pg/mL across the population, and both are within reference range. The problem is most obvious with testosterone. In the UK, the lower bound of "normal" total testosterone in adult men is often quoted as 8 nmol/L (about 230 ng/dL). A 35-year-old man at 9 nmol/L is technically in range. He is also, on most measures, hormonally a 75-year-old.
The shift over the last twenty years matters here too. Total testosterone in the average man has dropped roughly 1% per year since the late 1980s (Travison et al., JCEM, 2007). That means today's "normal" is yesterday's "low." The reference range moves down with the population. Yours should not.
The framework below uses optimal ranges drawn from clinical literature on healthy, symptom-free men — not statistical bands. They are tighter than what your lab will flag, and they are what we use throughout The Testosterone Blueprint.
Most NHS GPs will order a "testosterone" test, full stop. That gives you total testosterone and nothing else. If you pay for a private panel through a service like Medichecks, LetsGetChecked, or Thriva in the UK, or Everlywell in the US, you will usually get the full picture. Push for these four. Without them, the rest is guesswork.
This is the total amount of testosterone circulating in your blood, bound and unbound combined. It is the number most men know about — and the one that misleads the most.
Optimal range: 18–30 nmol/L (520–870 ng/dL)
A total testosterone of 12 nmol/L is technically inside most UK lab reference ranges. It is also, in most men under 60, associated with measurable symptoms — fatigue, low libido, mood flatness, slower recovery. Use the optimal range, not the lab range, as your reference.
One caveat: total testosterone alone cannot tell you whether you have a real androgen problem, because most of your testosterone is bound and biologically inactive. That is where the next number comes in.
SHBG is a protein produced by the liver that binds to testosterone in the bloodstream. Testosterone bound to SHBG is locked up — it cannot enter your cells, cannot act on your tissues, and effectively does nothing.
Optimal range: 15–35 nmol/L
This is the marker that explains most cases of "normal total T, terrible symptoms." If your SHBG is elevated — say 55 nmol/L — a large fraction of your total testosterone is locked up, leaving very little free testosterone to actually do its job. Conversely, if your SHBG is very low (below 15), you may have more free testosterone available than your total reading suggests, but low SHBG is itself associated with insulin resistance and metabolic problems.
SHBG rises with age, with low calorie intake, with high alcohol consumption, and with thyroid dysfunction. It falls with obesity, insulin resistance, and high androgen states.
This is the biologically active testosterone — the fraction not bound to SHBG or tightly bound to albumin. This is what actually reaches your androgen receptors and produces the effects you care about.
Optimal range: 0.30–0.50 nmol/L (300–500 pmol/L on some lab reports, or 8.7–25 ng/dL in US units)
Most labs do not measure free testosterone directly — they calculate it from total testosterone, SHBG, and albumin using the Vermeulen formula. This is fine. The calculation is accurate enough for clinical use. If your panel does not report it, you can run the numbers yourself with our free testosterone calculator using your total T, SHBG, and a default albumin of 4.3 g/dL.
If your free T is below 0.30 nmol/L and you have symptoms, you have a problem worth addressing — regardless of what your total testosterone says.
Oestradiol is the primary form of oestrogen in men. Yes, men make oestrogen, and a moderate amount is essential — for bone health, brain function, libido, and joint comfort. The mistake is treating it as the enemy.
Optimal range: 40–100 pmol/L (about 11–27 pg/mL)
Two things matter here: too low (below 40 pmol/L) blunts libido and damages bone density. Men who aggressively suppress oestrogen on TRT often report feeling worse, not better. Too high (above 100 pmol/L) can cause water retention, mood changes, and gynecomastia. It is also a sign of excess aromatisation — your body converting testosterone to oestrogen, which is more common in overweight men because fat tissue contains the aromatase enzyme.
The ratio of testosterone to oestradiol matters as much as either number alone. A man with total T at 25 nmol/L and E2 at 80 pmol/L is in a very different position from a man with the same T and E2 at 200.
If you have already paid for the four hormones above and you are still chasing answers, this next set is what to add. Most private panels include them as standard. NHS panels usually do not.
Luteinising hormone (LH) and follicle-stimulating hormone (FSH) are produced by the pituitary gland and tell your testicles to make testosterone and sperm respectively.
Optimal LH range: 2–8 IU/L
Optimal FSH range: 2–10 IU/L
These two numbers tell you where a testosterone problem originates. Low T + high LH/FSH = primary hypogonadism (the testicles are not responding to signals). This is the textbook case for TRT. Low T + low LH/FSH = secondary hypogonadism (the pituitary is not sending signals). This often responds to lifestyle change, weight loss, or treating an underlying issue. TRT may not be the right first move.
Skipping LH and FSH and going straight to TRT for a low total testosterone reading is one of the most common medical mistakes in this field. It treats the symptom without diagnosing the cause.
Prolactin is a pituitary hormone that, when elevated, suppresses testosterone production. A small fraction of low-T cases are actually prolactin-secreting pituitary tumours (prolactinomas) — usually benign, almost always treatable, but only if you find them.
Optimal range: under 350 mIU/L (about under 16 ng/mL)
If your prolactin is elevated and your testosterone is low, request a repeat test fasted and then an MRI referral if it is still high. This is one of the cases where a doctor's input is non-negotiable.
Hypothyroidism mimics low testosterone almost perfectly: fatigue, weight gain, low mood, low libido, cold intolerance. It is also far more common, especially in men over 40, than most GPs admit.
Optimal TSH: 0.5–2.0 mIU/L (lab ranges go up to 4.5, but symptoms appear above 2)
Optimal Free T4: in the upper half of the lab range
Optimal Free T3: in the upper half of the lab range
If your TSH is 3.5, your GP will tell you it is normal. It is also the level at which a significant fraction of men start feeling thyroid-related symptoms. The standard panel often only includes TSH, which is not enough on its own — TSH can be normal while Free T3 is low.
These are the markers that adjust how you interpret the hormone panel — or reveal what is dragging your hormones down.
Optimal: 75–150 nmol/L (30–60 ng/mL)
Vitamin D is, functionally, a hormone. It is required for testosterone synthesis. Men with vitamin D below 50 nmol/L have measurably lower total testosterone, and supplementation in deficient men raises T modestly. It is one of the few supplement interventions with consistent evidence behind it (see our supplement guide for what works and what doesn't).
If you live in the UK or Northern Europe and have not been supplementing through autumn and winter, your vitamin D is almost certainly low. A good vitamin D3 with K2 supplement is the simplest correction available.
Optimal: 50–150 ng/mL
Iron deficiency causes fatigue that looks identical to low T. It also reduces oxygen transport, recovery, and exercise capacity. Men can be deficient without obvious anaemia, which is why ferritin (the storage marker) is more useful than haemoglobin alone.
If your ferritin is below 30, address iron before assuming the problem is hormonal. Above 300, get checked for haemochromatosis — iron overload is a real condition and it suppresses testosterone in its own right.
Optimal: under 5.4% (under 36 mmol/mol)
Insulin resistance suppresses testosterone — directly, by reducing SHBG and increasing aromatisation, and indirectly, through the visceral fat that goes with it. HbA1c gives you a snapshot of where your blood sugar has been sitting over the past three months. A reading above 5.7% is pre-diabetic territory and almost always coexists with reduced testosterone.
If your HbA1c is elevated and your testosterone is low, fixing the metabolic problem will usually do more for your hormones than any direct intervention.
A full lipid panel does not directly tell you about testosterone, but it tells you about the system testosterone runs in. Cholesterol is the raw material for testosterone — your body makes T from it. Men who aggressively reduce dietary fat and run total cholesterol below 4 mmol/L (155 mg/dL) sometimes see their testosterone drop with it. The relationship is not linear, but the floor matters.
What you want to see: HDL above 1.2 mmol/L (45 mg/dL), triglycerides below 1.5 mmol/L (130 mg/dL). Elevated liver enzymes (ALT, AST, GGT) — usually from alcohol, fatty liver disease, or medication — affect SHBG production and hormone metabolism. If your GGT is high and you drink regularly, that is the lever to pull first.
A panel does not interpret itself. Here is the order I work through it in:
1. Free testosterone first, not total. If free T is in the optimal range and you feel fine, the panel is functionally normal regardless of what total says. If free T is low and you have symptoms, you have a problem.
2. If total T is low, look at LH/FSH. High signals + low output = testicular. Low signals + low output = pituitary or systemic. The treatment paths diverge sharply.
3. Check SHBG. If SHBG is high and pushing free T down, address what is causing the elevation — usually low calorie intake, alcohol, or hyperthyroidism — before treating the testosterone number itself.
4. Check oestradiol against testosterone. A T:E ratio out of balance can produce symptoms even when both numbers are individually "normal."
5. Rule out the mimics. Thyroid, prolactin, vitamin D, ferritin, HbA1c. Any of these can produce the same symptom picture as low T. Treating them often resolves it.
6. Look at the metabolic background. HbA1c, lipids, liver function. If the metabolic foundation is broken, hormonal interventions will underperform.
If two or three of those markers are out of range, you have your starting point. If most of them are within optimal range and you still feel terrible, the answer probably is not hormonal — it is sleep, stress, training load, or something the panel does not measure.
Lab values fluctuate. A single test can mislead, especially for testosterone, which is sensitive to time of day, sleep the night before, recent illness, and recent training. Some practical rules: always test 7–10am, fasted. Testosterone is highest in the early morning and falls 20–25% by mid-afternoon (JCEM, 2009). An afternoon test is not a real reading.
Confirm any low result with a second test, ideally two to four weeks apart. One reading is data; two readings is a pattern. Avoid testing within 48 hours of heavy training, drinking, or illness — all three depress testosterone temporarily. Retest 8–12 weeks after any intervention. Hormonal changes from lifestyle and supplements take time to show in blood. Retesting at week three will tell you nothing useful.
You will end up in one of three places.
The numbers are fine, the symptoms remain. Look beyond hormones. Sleep, stress, training, light exposure, mental health — all measurable, all treatable, none of them visible on a blood panel. Our companion guide to normal blood tests with low T symptoms covers this case in detail.
The numbers are clearly out of range and the lifestyle picture explains it. Fix the lifestyle picture first. Most low T resolves with sleep, training, food, and a basic supplement stack before TRT becomes a consideration.
The numbers are out of range and lifestyle is already optimised. This is when a serious conversation with an endocrinologist or a TRT-experienced clinician becomes appropriate. We have written separately on how to know whether TRT or natural optimisation is right for you.
The blood test is a snapshot. What you do next is the protocol. Read your numbers carefully, but do not let them define you. Ranges shift. Bodies adapt. The man you are at week one is not the man you are at week twelve, and the numbers will say so if you give them time.
Chapter 13 of The Testosterone Blueprint walks you through the complete blood panel, every marker explained, with optimal ranges, what they mean, and what to do about them. Plus printable cards B4 (reference ranges) and B5 (questions for your GP).
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