Total vs free testosterone: which number tells you if your T is low
Start with total testosterone. The Endocrine Society and the American Urological Association (AUA) both diagnose low testosterone from a total testosterone level drawn in the early morning, confirmed with a second morning test, and read alongside your symptoms. Free testosterone becomes the deciding number when your total is borderline or when something is likely shifting SHBG, the protein that binds testosterone, such as obesity, aging, thyroid disease or liver disease.
One number on one morning does not settle it. Symptoms alone do not confirm low testosterone either. A diagnosis rests on consistent symptoms plus consistently low results, and the rest of this guide shows you how to read each line of the report.
Total testosterone: the first number to read, and its cutoff
Total testosterone is everything in your bloodstream: the testosterone tightly bound to SHBG, the portion loosely bound to albumin, and the small fraction floating free. MedlinePlus notes that most testosterone in the blood is attached to proteins, which is why the total and free numbers can tell different stories.
The two major guidelines use slightly different cutoffs:
| Guideline | Total testosterone threshold | How to test |
|---|---|---|
| AUA 2018 | Below 300 ng/dL is a reasonable cutoff to support the diagnosis | Two separate early morning measurements, plus symptoms and signs |
| Endocrine Society 2018 | Harmonized lower limit of normal of 264 ng/dL, based on healthy nonobese young men | Fasting morning test, repeated to confirm, using an accurate, standardized assay |
Why the morning? Testosterone runs highest early in the day and drops later, so an afternoon draw can look low when your real level is fine. The Endocrine Society also advises against testing during an acute illness, because short term illness can temporarily suppress testosterone.
If both morning results come back low, the next step is usually LH and FSH, the pituitary hormones that tell the testes to make testosterone. Those results help separate a testicular cause (primary hypogonadism) from a pituitary or hypothalamic cause (secondary hypogonadism), which is how a clinician starts answering the bigger question of what is causing your low T.
Free testosterone: calculated vs measured by equilibrium dialysis
Free testosterone is the small share that is not bound to any protein. It is the portion your tissues can use directly, which is why it matters when total testosterone may be misleading.
There are three common ways a lab reports it, and they are not equally reliable:
| Method | How it works | What the Endocrine Society says |
|---|---|---|
| Equilibrium dialysis (measured) | Physically separates free from bound testosterone in the sample | Reference method; recommended |
| Calculated free testosterone | Formula using your total testosterone, SHBG and albumin | Acceptable alternative; recommended |
| Direct analog immunoassay | Single quick immunoassay for free testosterone | Considered inaccurate; not recommended |
Check the method line on your report. If it says "calculated", your lab also measured SHBG, and that SHBG number is worth reading. If it says "direct" or "analog", ask your clinician whether to repeat it with a better method before drawing conclusions.
You may also see "bioavailable testosterone" on some reports. MedlinePlus describes this as free testosterone plus the testosterone loosely bound to albumin, which tissues can also access.
How SHBG changes the picture
SHBG (sex hormone binding globulin) holds testosterone tightly. When SHBG rises, more testosterone is locked up and less is free, even if your total looks normal. When SHBG falls, your total can look low while your free testosterone is actually adequate.
The Endocrine Society guideline lists conditions that commonly move SHBG:
| SHBG tends to go down | SHBG tends to go up |
|---|---|
| Obesity | Aging |
| Diabetes | Liver cirrhosis and hepatitis |
| Hypothyroidism (underactive thyroid) | Hyperthyroidism (overactive thyroid) |
| Glucocorticoid (steroid) use | Some anticonvulsant medications |
| Nephrotic syndrome | Estrogen use, HIV infection |
Two practical patterns follow. A man carrying extra weight may have a low total testosterone partly because his SHBG is low, so free testosterone helps show whether he is truly deficient. An older man, or one with liver or thyroid disease, may have a normal total but low free testosterone because his SHBG is high. In both cases, total testosterone alone can point you in the wrong direction.
Units: converting ng/dL and nmol/L
US labs usually report total testosterone in ng/dL. Labs in Europe, Canada, Australia and many research papers use nmol/L. The conversion comes from the molecular weight of testosterone: divide ng/dL by about 28.84 to get nmol/L, or multiply nmol/L by 28.84 to get ng/dL.
| Total testosterone (ng/dL) | Approximate nmol/L |
|---|---|
| 200 | 6.9 |
| 264 | 9.2 |
| 300 | 10.4 |
| 500 | 17.3 |
| 800 | 27.7 |
Free testosterone comes in much smaller units, usually pg/mL or pmol/L, and sometimes ng/dL. One pg/mL is roughly 3.47 pmol/L. Always compare your free testosterone with the reference range printed by the same lab, because free testosterone ranges depend heavily on the method used.
Normal total but low free: what the guidelines say
This is the most common follow up question, and the answer is that it can matter. The Endocrine Society recommends measuring free testosterone, by equilibrium dialysis or an accurate calculation, when total testosterone is near the lower limit of normal or when SHBG is likely to be abnormal. In that situation, the free number is what helps confirm or rule out deficiency.
The AUA guideline anchors its diagnosis on total testosterone measured on two separate early mornings, together with symptoms and signs. So a single low free result with a comfortably normal total, and no matching symptoms, is not a diagnosis by itself.
The symptoms guidelines consider more specific include reduced sex drive, fewer morning erections, loss of body hair, smaller testes and breast tissue enlargement. Fatigue, low mood, poor concentration and reduced muscle strength are real but less specific, because sleep, stress, thyroid problems and depression can cause them too. If your free testosterone is low and you have those symptoms, that is a pattern a clinician should evaluate, including a repeat morning test and a look at SHBG, thyroid and liver markers.
Why reference ranges differ by lab and age
MedlinePlus points out that normal ranges vary from lab to lab. That happens for a few reasons:
- Different assays. Immunoassays and mass spectrometry can give different values for the same blood. The Endocrine Society recommends assays standardized for accuracy, which is why it published a harmonized range.
- Different reference populations. Some labs build ranges from all adult men, including older and heavier men. Others use young, healthy men. A range drawn from a less healthy population will have a lower floor.
- Age. Testosterone tends to drift down with age while SHBG drifts up, so free testosterone often falls more than total. Some labs print age specific ranges; many do not.
Age also shapes treatment decisions. The Endocrine Society does not recommend routinely treating every older man whose testosterone is low; it advises an individualized discussion of benefits and risks. A number inside the printed range does not prove you are fine, and a number just below it does not prove you need therapy.
How BioCure reads your report with you
A decade ago, most men only checked testosterone when something already felt wrong. Now more men want a baseline and a clear explanation of it. At BioCure Health, every diagnostic panel includes a specialist visit to interpret your results, so you are not left decoding total, free and SHBG on your own. The Comprehensive Male panel covers hormones, thyroid, lipids, metabolic and organ markers, the same context that explains why SHBG or testosterone may be off.
You can test with an at home kit and an in home phlebotomist visit, or at a lab, and results return in 7 to 14 days. The physician video consultation is $199, which can be credited back with a membership. If your results and symptoms support treatment, BioCure's testosterone program has three tiers: bioOptimize (foundational), bioRestore (medications that raise your body's own testosterone without direct hormone replacement) and bioTest (full testosterone replacement with ongoing hormone monitoring). BioCure is physician led, licensed in 47 states, and does not bill insurance directly, though many patients use HSA or FSA funds with the documentation BioCure provides.
Frequently asked questions
Is total or free testosterone more important for diagnosing low T?
Total testosterone comes first; both the Endocrine Society and the AUA build the diagnosis on morning total testosterone confirmed by a repeat test. Free testosterone becomes important when your total is near the lower limit or when SHBG is likely high or low. Read them together, not in isolation.
What testosterone level is considered low?
The AUA uses total testosterone below 300 ng/dL as a reasonable cutoff, measured on two separate early mornings. The Endocrine Society uses a harmonized lower limit of 264 ng/dL based on healthy young men. Symptoms must also be present for a diagnosis.
Why do I need two morning blood tests for testosterone?
Testosterone peaks in the morning and varies from day to day, and illness, poor sleep or a late draw can push one result down. Guidelines require a confirmed low result before diagnosing deficiency. A single low number may simply be a bad day.
Can my total testosterone be normal but free testosterone low?
Yes. This usually happens when SHBG is high, which is more common with aging, liver disease, an overactive thyroid or some medications. The Endocrine Society recommends checking free testosterone by equilibrium dialysis or calculation in these cases, and a clinician should review it alongside your symptoms.
How do I convert testosterone from nmol/L to ng/dL?
Multiply nmol/L by about 28.84 to get ng/dL, or divide ng/dL by 28.84 to get nmol/L. For example, 10.4 nmol/L is about 300 ng/dL. Free testosterone uses smaller units such as pg/mL or pmol/L.
What does a high or low SHBG mean on my testosterone results?
High SHBG binds more testosterone, so less is free even if your total looks normal. Low SHBG, common with obesity, diabetes and an underactive thyroid, can make total testosterone look low while free testosterone is adequate. That is why SHBG changes how you read the other two numbers.
Your lab report is not a verdict; it is a set of clues. Read total testosterone first, check how free testosterone was measured, look at SHBG for the reason the two disagree, and confirm anything low with a second morning test. Longevity is not accidental, it is intentional, and it starts with understanding your own numbers.
Let BioCure Health lead you in the right direction. Call or text us to schedule an introductory call at 754-206-0838, your future self will thank you.