Your GP rings to tell you your testosterone is 16 nmol/L. You feel terrible, no energy, no drive, soft in the middle. He tells you it's normal. You go home confused, thinking one of you is mad.
This happens because your GP is looking at total testosterone. And total testosterone is, frankly, a poor proxy for what's actually happening in your body. What matters is free testosterone, the fraction that's not locked up and useless.
The most dramatic example I've seen: a 47-year-old client with total T of 19.2 nmol/L (GP said "perfectly normal") but SHBG of 68 nmol/L. His calculated free testosterone was 0.21 nmol/L — genuinely low. Once we addressed the high SHBG through body composition work and thyroid optimisation, free T climbed to 0.38 nmol/L without any medication. His energy and libido returned within two months.
Let me walk you through this, because it changes everything about how you understand your hormones.
The Three Forms of Testosterone in Your Blood
Your body doesn't send testosterone round your bloodstream naked. It gets bound to proteins like cargo on a lorry. There are three fractions:
Albumin-bound testosterone (~60% of total) binds loosely to the protein albumin. This is weakly bound, tissue can prise it loose when needed.
SHBG-bound testosterone (~30-40% of total) binds tightly to sex hormone-binding globulin. This is the locked-away fraction. Your tissues can't use it.
Free testosterone (~1-3% of total) genuinely floats free in your blood, ready to hit androgen receptors in your muscles, brain, and fat.
Only the free and albumin-bound fractions matter functionally. The SHBG-bound stuff is dead weight.
Here's the practical reality: you can have 16 nmol/L total testosterone and feel fantastic if your free testosterone is high. Or you can have 18 nmol/L and feel like a ghost if your SHBG is sky-high, trapping most of it.
Your GP orders total testosterone because it's cheap and standard. Not because it's useful.
Vermeulen et al. - A critical evaluation of methods for free testosterone
Free testosterone calculated from total testosterone, SHBG, and albumin provides a clinically meaningful measure that better reflects androgenic status than total testosterone alone.
Why SHBG Is the Hidden Driver
SHBG is the troublemaker. It binds testosterone and says "you're not using this."
Several things drive SHBG up:
Obesity and insulin resistance. Insulin actually suppresses SHBG production. The heavier you are, the less insulin-resistant you become (in fat men especially), SHBG drops, but your total testosterone also tends to plummet. Net result: you're screwed either way. Fix the obesity first.
Alcohol. Regular drinking elevates SHBG. This is one reason heavy drinkers often have low free testosterone despite reasonable total numbers. Cut the booze for 8 weeks and retest.
Thyroid dysfunction. High SHBG is common in hyperthyroidism. If you're hyper, fix that first.
Age. SHBG rises as you get older, naturally trapping more testosterone. This is one reason men over 50 often feel testosterone-deprived even when total levels look adequate.
Oestrogen dominance. Excess oestrogen (from body fat or poor methylation) can elevate SHBG.
Calculating Free Testosterone: The Vermeulen Formula
Here's where it gets practical. You can't directly measure free testosterone accurately with a standard blood test, the lab methods damage the fragile free fraction. But you can calculate it from total testosterone, SHBG, and albumin using the Vermeulen formula.
Most good private labs (Medichecks in the UK, for instance) will report it if you order the right panel. Ask for:
- Total testosterone
- SHBG
- Albumin
- Free testosterone (calculated)
If your GP's labs don't calculate it, take the numbers to a private clinic or use Medichecks' testosterone panel (around £60). Plug total T and SHBG into an online Vermeulen calculator. You'll get a realistic picture.
What's Actually Optimal?
Total testosterone: 12-30 nmol/L is the reference range. Most feeling-good men sit 18-25.
Free testosterone: 0.3-1.0 nmol/L (or roughly 200-500 pg/mL in older units). This is where the action is.
SHBG: 30-100 nmol/L. Higher SHBG means less available testosterone per unit total.
A man with 15 nmol/L total but SHBG of 40 might have 0.35 nmol/L free, perfectly decent. Another with 20 nmol/L but SHBG of 120 might have only 0.15 nmol/L free, symptomatic.
If Your Free T Is Low but Total T Is Normal
This is the classic scenario. Total testosterone looks fine. You feel dreadful. Here's your action plan:
1. Get SHBG down. Lose body fat if you're overweight. Cut alcohol to 2-3 units per week. Fix your thyroid if it's off. These alone often bring SHBG down 20-30%.
2. Liver support. Your liver metabolises oestrogen. Poor liver function (fatty liver, poor diet) can leave oestrogen running high, which elevates SHBG. Two months of clean eating, moderate alcohol, and no seed oils often helps.
3. Check your thyroid properly. Free T3, Free T4, and TPO antibodies. Hypothyroidism raises SHBG; hyperthyroidism raises it further.
4. Consider supplementation. Calcium d-glucarate (500mg daily) and DIM (100-200mg daily) support oestrogen metabolism. These won't magic up free testosterone, but they can help.
5. If nothing budges and you're symptomatic, consider testosterone replacement. This is a conversation for a proper clinic, not your GP.
The Bottom Line
Your total testosterone number is roughly as useful as knowing the total weight of a car without knowing how much is actual cargo versus packaging. Free testosterone is what matters. SHBG is the thief. Get it measured, understand your own numbers, and stop assuming your GP's normal-range verdict means you're fine.
Free testosterone — not total — is what actually hits your androgen receptors and drives how you feel; if your GP only tests total T, demand SHBG and free T as well.
Order a proper panel from Medichecks (affiliate link, they're solid). Calculate your free T. Address the obvious stuff first: body composition, alcohol, sleep. Then reassess. You might find you feel like yourself again without ever needing medication.
Related Guides
- Why Your Testosterone Drops 1% Every Year After 30, And What Actually Matters
- SHBG Explained: Why Your Total Testosterone Number Is Almost Meaningless
- Body Fat and Testosterone: Why Your Waist Size Is Wrecking Your Hormones
- Cortisol and Testosterone: Why Chronic Stress Is Quietly Wrecking Your Hormones
