The testosterone blood test explained: total, free and what your number means
How total and free testosterone tests work, why timing matters, what a result below 300 ng/dL can mean, and which laboratory tests may come next.
A testosterone test looks like a simple thing to order. One vial, one number, one answer.
It rarely works out that way. The time of day the blood was drawn, the form of testosterone that was measured and the laboratory that ran it all affect what comes back. Testing is easy. Interpreting the result is the difficult part.
Here is what the test measures, the conditions that make a result usable, and how the number fits into a diagnosis.
When a testosterone test is worth ordering
Cleveland Clinic lists the symptoms that usually prompt the test in men past puberty: erectile dysfunction, infertility, low libido, loss of armpit and pubic hair, low muscle mass and gynecomastia (Cleveland Clinic).
Tiredness, low mood and a thickening waist are the complaints men more often arrive with, and they are absent from that list, because on their own they point in too many directions. Our guide to the signs of low testosterone separates the symptoms that track hormones from the ones that mislead, and erectile difficulty has a guide of its own, since it carries cardiovascular meaning as well.
Symptoms are not a perfect filter in either direction. Not every man with a low level has symptoms, and the only way to know your level is to measure it (Cleveland Clinic).
What the test actually measures
Most of the testosterone circulating in your blood is bound to protein. Some is held tightly by sex hormone binding globulin (SHBG). Some is bound loosely to albumin and comes free more easily. A small share circulates unbound.
That gives three ways to report it:
- Total testosterone. Everything, bound and unbound. This is the standard first test.
- Free testosterone. The unbound portion only, which can be more helpful for diagnosing certain conditions (Cleveland Clinic).
- Bioavailable testosterone. Generally the free fraction plus the albumin-bound fraction.
Total testosterone is the right starting point for almost everyone.
When free testosterone helps
SHBG is the reason the free test exists. Obesity tends to lower it, while aging, liver disease and thyroid problems tend to raise it. When SHBG is shifted, a total result can look reassuring while the usable fraction is low, or the other way around.
The Endocrine Society suggests obtaining a free testosterone concentration in men whose total is near the lower limit of normal, or who have a condition that alters SHBG (JCEM, 2018).
| Your situation | Is total testosterone enough? |
|---|---|
| Comfortably normal total, no SHBG-shifting condition | Usually yes |
| Total near the lower limit of the laboratory range | Free testosterone and SHBG may add information |
| Obesity or type 2 diabetes, which tend to lower SHBG | Free testosterone and SHBG may add information |
| Aging, liver disease or thyroid disease, which tend to raise SHBG | Free testosterone and SHBG may add information |
The method matters as much as the order. The Endocrine Society specifies equilibrium dialysis, or an estimate calculated from total testosterone, SHBG and albumin using an accurate formula. Direct analog immunoassays are considered less reliable. If a free testosterone result is going to influence a decision, ask which method produced it.
How to get a usable result
Two conditions decide whether a reading can carry any weight.
An early morning, fasting sample. Testosterone is highest in the early part of the day, which is why the Endocrine Society specifies a fasting morning measurement with an accurate, reliable assay as the initial diagnostic test (JCEM, 2018). Laboratories differ on the exact window and on fasting instructions, so follow the ones you are given. If you work nights or sleep at unusual hours, ask the laboratory or your doctor how to time the draw relative to your own sleep.
A second measurement. The American Urological Association recommends that the diagnosis be made only after two total testosterone measurements taken on separate occasions, both in the early morning (AUA guideline). Where possible, use the same laboratory for both, since assays and reference ranges differ between them.
Why the test needs repeating
Testosterone moves. Researchers who sampled the same men repeatedly found that two measurements from one man differed by more than 18% to 28% roughly half the time, and by more than 27% to 54% about a quarter of the time. Their conclusion was that a single sample is generally not enough to characterize a man's hormone levels (Clin Endocrinol, 2007).
The question a doctor is trying to answer is not whether your testosterone was low once, but whether it is low consistently, alongside symptoms or signs that fit.
| What can move the number | How to read it | What it calls for |
|---|---|---|
| A sample taken later in the day | Can temporarily influence the result | Repeat at the time your laboratory advises |
| Acute illness | Can temporarily influence the result | Test once you are well again |
| Severe sleep loss or acute physiological stress | Can temporarily influence the result | Note it, and discuss timing before retesting |
| Ordinary day-to-day variation | Expected, and often large | A second early morning sample |
| Medications and other health conditions | Can affect the result in either direction | Bring the full list to the appointment |
| A problem in the testicles, or in the pituitary and hypothalamus | A possible underlying cause rather than a temporary influence | Further tests to work out which |
An abnormal result does not by itself mean you have a medical condition. Medications, other conditions and errors in processing all feed into it, and your history is part of the interpretation (Cleveland Clinic).
How to prepare
- Book an early morning appointment, and follow the laboratory's own timing and fasting instructions.
- Avoid testing during an acute illness. If you have recently been unwell, wait until sleep, appetite and routine are back to normal, or ask when to retest.
- Take a full list of your medicines and supplements, prescription and otherwise. Do not stop anything on your own account.
- If a repeat is likely, book it at the same laboratory.
- Ask for the printed report, including the reference range and, if free testosterone was ordered, the method used.
How to read the number
The AUA uses a total testosterone below 300 ng/dL as a reasonable cut-off supporting a diagnosis of testosterone deficiency, and is explicit that the clinical diagnosis is made only when a low level occurs together with symptoms or signs. Reference ranges and methods vary between laboratories, so your own report's range is the one that applies to your result (Cleveland Clinic).
| Your result | What it usually means | Sensible next step |
|---|---|---|
| Below 300 ng/dL, with symptoms | Consistent with possible testosterone deficiency, not yet confirmed | Repeat on a second morning, then discuss causes with a doctor |
| Below 300 ng/dL, no symptoms | A number, not a diagnosis | Repeat, and look for an explanation such as illness, sleep or weight |
| Near the lower end of your laboratory's range, with symptoms that fit | Unsettled. Assay, reference range and SHBG all affect how it reads | Repeat, and ask whether free testosterone and SHBG would add anything |
| Comfortably normal, with symptoms | Testosterone is unlikely to be the explanation | Look at sleep, thyroid, iron, mood, alcohol and medications |
Interpretation depends on more than the figure itself: the symptoms it sits beside, the repeat result, the assay, the laboratory's range and, in the right context, SHBG and free testosterone. Chasing a higher number inside the normal range is not a medical goal.
ng/dL, nmol/L and reference ranges
Reports outside the United States usually print nmol/L rather than ng/dL. The conversion is arithmetic: divide ng/dL by about 28.8, which puts the 300 ng/dL decision point at roughly 10.4 nmol/L.
Ranges themselves vary between laboratories and assays, and with age (Cleveland Clinic). The same figure can sit inside one laboratory's range and below another's, which is why the range printed next to your result is the one worth reading.
What doctors may test next
A confirmed low result raises the question of cause. The AUA recommends measuring luteinizing hormone (LH) in men with low testosterone, and prolactin when LH is low or low-normal. LH helps separate a problem in the testicles from a problem with the signal from the brain, and that distinction changes what happens next.
Before testosterone therapy, the AUA also calls for hemoglobin and hematocrit, and a PSA in men over 40. The Endocrine Society lists several situations in which therapy should not be started without further evaluation, among them plans for fertility in the near term, prostate or breast cancer, a raised PSA that has not been investigated, an elevated hematocrit, untreated severe sleep apnea, severe urinary symptoms, uncontrolled heart failure, and a heart attack or stroke within the previous six months (JCEM, 2018). That list is a prompt for a proper assessment, not a substitute for one.
Depending on symptoms, a workup often adds thyroid function, HbA1c or fasting glucose, ferritin and a lipid panel. Fatigue and low drive have several possible causes, as our guide to persistent tiredness sets out, and testing testosterone alone is how the others get missed.
Questions to ask your doctor
- Was this a fasting early morning sample, and when should it be repeated?
- What is this laboratory's reference range, and which assay produced my number?
- If free testosterone was measured, was it equilibrium dialysis or a calculated estimate?
- Have we looked for a cause, rather than stopping at the level itself?
- Could any of my medicines or other conditions be affecting this result?
Testosterone test checklist
- Book an early morning, fasting draw, following your laboratory's instructions.
- Postpone the test if you are acutely unwell.
- Repeat a low result at the same laboratory before drawing conclusions.
- Read the number against your own report's range and your symptoms.
- Take the printout to a doctor if the level is genuinely low, since some causes are reversible.
At-home kits sit in a middle position. Their quality depends on the sample type, the timing of collection, the assay and the laboratory behind them, and Cleveland Clinic notes that accuracy varies and advises against self-diagnosis (Cleveland Clinic). A result from one can be a reasonable prompt to get tested properly. It is not a diagnosis, and a low reading still needs confirmation with a properly timed laboratory measurement and a clinical review.
That is also the argument against buying a supplement on the strength of one reading. Most testosterone boosters do nothing, and an unconfirmed number is a poor reason to start.
Frequently asked questions
What is a normal testosterone level for a man?
There is no single universal number. Laboratories use different assays and print different reference ranges, so your result should be read against the range on your own report. As a decision point, the American Urological Association treats a total testosterone below 300 ng/dL as a reasonable cut-off supporting a diagnosis, and a clinical diagnosis also requires repeat early morning measurements together with symptoms or signs.
Why does the timing of a testosterone test matter?
Testosterone follows a daily rhythm and is highest in the early morning, so an afternoon sample can read lower in a man whose levels are normal. Guidelines prefer a fasting early morning sample for diagnostic assessment. An unexpectedly low result from another time of day is usually repeated at the right time rather than acted on.
Do I need to test free testosterone as well?
Not routinely. The Endocrine Society suggests measuring free testosterone when the total sits near the lower limit of normal, or when a condition is likely to alter SHBG, such as obesity, thyroid disease, liver disease or older age. How it is measured matters, so ask whether the result came from equilibrium dialysis or an accurate calculation.
Can one low testosterone result be wrong?
A single measurement is a poor description of a man's usual level. When researchers sampled the same men repeatedly, two readings differed by more than 18% to 28% about half the time. That is why guidelines ask for repeat early morning testing, ideally at the same laboratory, before any conclusion is drawn.
References
- Evaluation and Management of Testosterone Deficiency: AUA Guideline · American Urological Association
- Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline · The Journal of Clinical Endocrinology & Metabolism, 2018
- Testosterone Test · Cleveland Clinic
- Intraindividual variation in levels of serum testosterone and other reproductive and adrenal hormones in men · Clinical Endocrinology, 2007