Testosterone is a steroid hormone made mainly in the testes in men and in the ovaries and adrenal glands in women. The blood test measures the total or free fraction, and it is ordered when hormone function is being assessed. Timing, age, sex, and method matter, and the range printed on your report decides how the value is read.
Testosterone is one of the hormones most likely to be compared across years, and one of the easiest to misread when two reports were collected at different times of day or measured by different methods.
What the test measures
Testosterone is an androgen, a steroid hormone that influences muscle and bone, body hair, libido, mood, and sperm production. In men, most of it is made by cells in the testes, with a smaller contribution from the adrenal glands. In women, the ovaries and adrenal glands produce smaller amounts, and those amounts still matter for the same tissues.
In blood, most testosterone is bound to proteins: sex hormone binding globulin, usually shortened to SHBG, and albumin. Only a small fraction circulates unbound. Total testosterone measures the bound and free hormone together. Free testosterone measures the unbound part, and some reports print a calculated free androgen index or a bioavailable testosterone estimate instead. Each of those is a different measurement or calculation, and each is read against its own range.
Why it may be ordered
- As part of a hormone panel, with cortisol and prolactin, or with LH and FSH.
- When a clinician is assessing low energy, reduced libido, or changes in body hair and muscle, alongside the rest of the assessment.
- When fertility is being investigated, in men or in women.
- When puberty is being assessed, because testosterone changes markedly through it.
- When acne, excess hair growth, or menstrual changes are being assessed in women, where androgens are part of the picture.
- When a known hormone condition is being followed over time.
The unit on your report
| What you may see | Unit | What it reflects |
|---|---|---|
| Testosterone, total testosterone, T | ng/dL | The total hormone concentration in serum, bound and free, in nanograms per decilitre. |
| Testosterone, total testosterone | nmol/L | The same measurement in nanomoles per litre. The two scales are not the same number. |
| Free testosterone, free T | pg/mL or pmol/L, as the laboratory reports | The unbound fraction, which some laboratories measure and others calculate. |
| Bioavailable testosterone | ng/dL or nmol/L, as the laboratory reports | The fraction that is not bound to SHBG, estimated from total testosterone and SHBG. |
| Free androgen index | unitless | A calculated ratio of total testosterone to SHBG. |
Some reports print total testosterone and SHBG and leave the free fraction to be calculated. Others print a calculated value directly. Read the range beside the line you are looking at, because a range for total testosterone does not apply to a free testosterone result.
Why this page does not print a range
Testosterone ranges differ by laboratory and method, and the method matters more here than for many tests: some laboratories use immunoassays and others use mass spectrometry, and the two can give different results on the same sample. Ranges also differ by sex, by age, and by the time of day the sample was collected, and some reports print age-banded ranges. Pregnancy and the use of oestrogen-containing medicines raise SHBG and change total testosterone.
The range printed on the report that produced your value is the one that applies. Doctano keeps that printed range with the result and does not replace it with a general range. When a report prints age-banded ranges, the one that matches your age and sex is the one to read.
What a high value can mean
A result above the report's range means the testosterone concentration is higher than the laboratory's interval. In men, possible contributors include testosterone or anabolic steroid use, and rare conditions in which the testes or adrenal glands produce excess hormone. In women, possible contributors include polycystic ovary syndrome, congenital adrenal hyperplasia, and rare hormone-producing conditions.
A high total testosterone can also reflect a high SHBG rather than more free hormone, which is why a report may print SHBG or a free fraction alongside the total. The result does not confirm or rule out any of these, and a clinician reads it with the clinical picture and the other hormone results.
What a low value can mean
A result below the report's range means the testosterone concentration is lower than the laboratory's interval. In men, possible contributors include conditions affecting the testes or the pituitary gland, obesity, severe illness, some medicines including opioids and glucocorticoids, and ageing. In women, low testosterone is less clearly defined, and the result is interpreted with more caution.
A low result can also be a matter of timing. Testosterone tends to be higher in the morning, and a sample collected later in the day can be lower than a morning sample from the same person. Illness and poor sleep can lower it too. A single low value does not establish a hormone condition, and a clinician reads it with symptoms, other hormones, and the collection time.
What can move the value
- Time of day. Testosterone tends to be higher in the morning, and the pattern is clearest in men.
- Day-to-day variation. Values fluctuate between samples, so one result is a snapshot.
- SHBG. Liver disease, thyroid changes, obesity, ageing, and oestrogen-containing medicines change SHBG and therefore total testosterone.
- Illness and sleep. Acute illness and poor sleep can lower the measured value.
- Medicines. Opioids and glucocorticoids can lower testosterone, and a clinician can say whether a medicine is relevant.
- Assay and calibration. Different laboratories and methods can produce different results on the same sample.
What to compare it with
Read testosterone with LH and FSH, which show how the pituitary is signalling the gonads; with SHBG, which explains a total value that seems out of step with the clinical picture; and with prolactin, because a raised prolactin can affect gonadal function. In women, the result is read with the menstrual history and with other androgens. The same laboratory, the same method, and a similar collection time make two results easier to compare.
How to see the trend
Doctano reads the testosterone value, its unit, and the reference range printed on the report. It keeps the range with the result, normalizes the marker name across laboratories, and places the value on the profile's timeline. Where the report prints the collection time, that stays with the value.
Because testosterone is reported in different units and measured by different methods, verify the value and the unit against the original report before comparing two results. A change is easier to trust when both samples came from the same laboratory at a similar time of day.
What this page is not
This page explains the test in general. It does not interpret your result, diagnose a condition, or recommend treatment. It is not medical advice. Verify the value and the unit against the original report, and discuss the result with a qualified professional.