Testosterone Total measures the full amount of testosterone circulating in a serum sample, protein bound and unbound counted together. It is the default testosterone line on almost every panel. Typical lab reference ranges run roughly 264 to 1200 ng/dL in men and 8 to 120 ng/dL in women, and ranges vary by lab, age and sex. FitScript's optimal range is 500 to 900 ng/dL in men and 15 to 70 ng/dL in women, and optimal ranges are FitScript's optimization targets, not diagnostic cut-offs. The Endocrine Society clinical practice guideline recommends a morning sample and confirmation of a low value on a separate day before conclusions are drawn 1. The marker page carries the full detail on ranges and results. The rest of this guide is about names.
Testosterone is most often printed as 'Testosterone, Total', 'Total Testosterone' or 'Testosterone, Serum', and depending on what was ordered it can also appear as 'Free Testosterone', 'Bioavailable Testosterone', 'Testosterone, Free and Total', or as a calculated index derived from testosterone and SHBG.
The variation is not medical, it is clerical. Laboratories name analytes according to their own catalogue, and the printed line often combines three separate pieces of information in one string. There is the analyte itself (testosterone), the fraction being reported (total, free, bioavailable), and sometimes the method (LC/MS-MS, equilibrium dialysis, direct). A line reading 'Testosterone, Free, Equilibrium Dialysis' and a line reading 'Free Testosterone (Direct)' are both free testosterone, but they were produced in very different ways.
Some panels also add a population qualifier, such as a high sensitivity or female specific assay. That does not change the hormone being measured, only the analytical sensitivity the laboratory applies to it.
| Line on the report | What that line measures |
|---|---|
| Testosterone, Total / Total Testosterone / Testosterone, Serum | All testosterone in the sample, protein bound plus unbound |
| Testosterone, Free (Direct) | The unbound fraction, estimated with an analog immunoassay |
| Testosterone, Free (Equilibrium Dialysis) | The unbound fraction, physically separated before measurement |
| Free Testosterone, Calculated | The unbound fraction estimated from total testosterone, SHBG and albumin |
| Bioavailable Testosterone | The free fraction plus the loosely albumin bound fraction |
| Testosterone, Free and Total / Free, Total and Bioavailable | A bundled order showing several fractions on one panel |
| Testosterone, Total, LC/MS-MS (or MS) | Total testosterone measured by mass spectrometry |
| Testosterone, high sensitivity / female / paediatric | The same analyte on an assay tuned for low concentrations |
| SHBG (sex hormone binding globulin) | The main carrier protein, not testosterone itself |
| Free Androgen Index (FAI) | A ratio of total testosterone to SHBG, not a concentration |
| Albumin | A second carrier protein, used inside free testosterone calculations |
If you cannot match your report to this table, the method name printed underneath the result, or the footnote at the bottom of the page, usually resolves it.
The total includes every molecule of testosterone in the sample, whether it is travelling bound to a protein or circulating free. Most of it is not free. The majority is held by sex hormone binding globulin (SHBG), which binds testosterone tightly, and a large further share rides on albumin, which binds it loosely. Only a small remainder circulates completely unattached.
That distribution is why one number can be read in two ways. Two people with an identical total can have quite different amounts of hormone available to tissue if their carrier protein levels differ. Research suggests that SHBG binding is more dynamic than the classical single site model assumed, which matters because most free testosterone calculations are built on that older model 2.
For most people with unremarkable carrier proteins, total testosterone remains the practical starting point. It is the measurement clinical guidelines are written around 1. The fractional lines exist to answer the question total alone cannot answer, which is how much of that hormone is actually accessible.
Free testosterone is listed separately because the tightly bound portion of the total is not freely available to tissue, so the free line estimates the share that is not anchored to SHBG. It is reported in different units from the total, usually pg/mL or pmol/L, which is one reason the two numbers look nothing alike on the page.
There are three common ways to produce that number. Equilibrium dialysis physically separates the unbound hormone before measuring it and is generally regarded as the reference approach. Calculated free testosterone uses total testosterone, SHBG and albumin in an equation. Direct analog immunoassays estimate it in a single step and are the cheapest option. Studies indicate that free testosterone values differ depending on which of these approaches was used and on the binding model behind the calculation, so method matters when you compare results 3.
Practically, this means a free testosterone number is only interpretable alongside the method that produced it. A calculated value from one panel and a dialysis value from another are not interchangeable, and tracking a trend works best when the same laboratory and the same method are used each time.
Bioavailable testosterone is the free fraction plus the loosely albumin bound fraction, reported as a single number. The reasoning is that albumin releases testosterone readily as blood passes through tissue, so albumin bound hormone behaves more like available hormone than the tightly held SHBG bound portion does.
It is measured either by precipitating the SHBG bound fraction out of the sample, or by calculation from total testosterone, SHBG and albumin. Laboratories report it in ng/dL or nmol/L, the same units as the total, which sometimes confuses readers who see two similar looking numbers stacked on one page.
Bioavailable testosterone tends to be ordered when carrier protein levels are expected to be unusual, for example in older adults, in people with obesity or insulin resistance, in people with thyroid or liver conditions, and in people using oral estrogen, all of which shift SHBG. In those situations the total alone can be misleading in either direction, and a fractional measurement gives a clinician more to work with 2. It is a complement to the total, never a replacement for it.
SHBG appears beside testosterone because it determines how much of the total is accessible, and because every calculated free or bioavailable value needs it as an input. Without SHBG, a calculated free testosterone cannot be produced at all, which is why ordering free testosterone frequently adds an SHBG line to the report automatically.
SHBG is a liver made glycoprotein, and its concentration moves with age, thyroid status, liver function, insulin sensitivity, body composition and estrogen exposure. It tends to rise with age and with thyroid overactivity, and tends to fall with obesity and insulin resistance. Higher SHBG is associated with a lower free fraction at the same total testosterone, so the two lines can move in opposite directions on the same report 2.
This is the single most common source of confusion for people reading their own results. A total sitting comfortably inside the reference range alongside a low free value, with a high SHBG underneath, is a recognisable pattern. It is not a diagnosis of anything. It is an observation that the distribution of the hormone, rather than the quantity of it, is what deserves the conversation with a clinician.
Several other hormones are often printed in the same block and are routinely mistaken for testosterone itself. They are related, but each measures something different.
DHEA-S is an adrenal precursor, abundant in circulation and frequently ordered alongside testosterone when the adrenal contribution to androgen levels is in question. Androstenedione is another precursor sitting upstream of testosterone. DHT, dihydrotestosterone, is the more potent downstream product formed in tissue. Estradiol appears because testosterone is converted to it by aromatase, and the balance between them is part of the picture clinicians consider.
LH and FSH are pituitary signals rather than androgens, and they are measured to work out whether a low testosterone result originates in the testes or in the pituitary and hypothalamus, a distinction the clinical guideline treats as central to evaluation 1. Prolactin is sometimes added for the same reason.
A newer group is also worth knowing about. Research suggests that 11-oxygenated androgens of adrenal origin, including 11-keto-testosterone, contribute to circulating androgen activity and are not captured by a conventional testosterone measurement 4. They are not on standard panels yet, but they explain why androgen related findings sometimes do not line up neatly with a normal testosterone result.
Laboratories differ because two measurement conventions coexist, the conventional system using mass per volume and the SI system using moles per volume. Neither is more correct, and conversion between them is straightforward arithmetic once you know which unit applies to which fraction.
| Unit | Usually attached to | Conversion |
|---|---|---|
| ng/dL | Total and bioavailable testosterone | 1 ng/dL is about 0.0347 nmol/L |
| nmol/L | Total and bioavailable testosterone (SI) | 1 nmol/L is about 28.8 ng/dL |
| ng/mL | Total testosterone, less common | 1 ng/mL equals 100 ng/dL |
| pg/mL | Free testosterone | 1 pg/mL is about 3.47 pmol/L |
| pmol/L | Free testosterone (SI) | 1 pmol/L is about 0.288 pg/mL |
| nmol/L | SHBG | Reported in nmol/L almost everywhere |
| Percent or index | Percent free testosterone, free androgen index | A ratio, not a concentration |
The free androgen index deserves a note because it looks like a measurement and is not one. It is total testosterone in nmol/L divided by SHBG in nmol/L, multiplied by one hundred. It is cheap to produce and widely reported, but it is a derived ratio whose usefulness depends heavily on the population it is applied to.
Units also explain a common scare. A free testosterone of 15 pg/mL and a total testosterone of 500 ng/dL describe the same blood, but a reader comparing the raw digits without checking units can conclude something alarming that is not there.
The method changes the number enough that laboratories print it in the analyte name, which is why you see suffixes such as LC/MS-MS, MS or ED on the report. Two broad families are in use. Immunoassays rely on antibody binding and run quickly on high volume analysers. Liquid chromatography with tandem mass spectrometry separates the molecule physically before measuring it and is generally regarded as the more specific approach.
Research suggests that immunoassays lose accuracy at the low end of the measuring range, which is exactly where samples from women, children and strongly suppressed adult men fall 5. Evidence suggests that reliable measurement in women requires assays validated at low concentrations, because many routine platforms were calibrated around the adult male range 6.
There is also a history problem. Research suggests that between method differences have historically been large enough that results from different platforms should not be compared directly without knowing how each was calibrated 7. Standardisation efforts have narrowed those gaps, but the practical rule for an individual reader has not changed. Compare your result to the reference interval printed on your own report, and track changes over time at the same laboratory using the same method, not across laboratories.
A result outside the printed reference interval is an observation that needs context, never a conclusion on its own. The useful habit is to read it in three steps, what the value shows, what it might reflect, and what is worth raising with a clinician.
A low total testosterone with a low free value may reflect reduced production, and the guideline approach is to repeat it on a morning sample on a separate day before anything further, because single values fluctuate and acute illness suppresses the axis 1. A low total with a normal free value and a high SHBG often reflects carrier protein distribution rather than production. A normal total with a low free value and high SHBG is the mirror image of that pattern.
In men, an unexpectedly high total can reflect exogenous androgen exposure, assay interference, or simply an unusual draw.
A suboptimal value is not an emergency, but a result far outside the reference interval, or any result accompanied by significant symptoms, is worth discussing with a clinician promptly rather than waiting for the next panel.
Quite a lot moves it, which is why one result is a snapshot rather than a verdict. Testosterone follows a daily rhythm, running highest in the morning and declining through the day, and that rhythm is more pronounced in younger men. This is the main reason guidelines specify a morning draw in the fasting state and a repeat measurement before conclusions are reached 1.
Short term influences include sleep restriction, acute illness or infection, recent very heavy training, significant caloric restriction, alcohol intake and psychological stress. A glucose load can lower measured values, which is part of the rationale for fasting samples. Longer term influences include body composition and insulin sensitivity, both of which act partly through SHBG, as well as thyroid status and liver function. Any medication question belongs with the prescribing clinician.
Analytical variation adds a further layer on top of the biological variation 7. The practical consequence is simple. Standardise your own conditions as far as you can, draw in the morning, avoid testing during illness or immediately after an unusually hard training block, and judge direction across several results rather than reacting to one.
The fractional lines and the carrier proteins come first, because they decide how the headline number should be read. SHBG and albumin let a free or bioavailable value be calculated and explain most mismatches between total and free 2.
From there, LH and FSH indicate whether a low value originates at the testes or at the pituitary level, a distinction the clinical guideline places at the centre of evaluation 1. Estradiol shows how much is being aromatised. Prolactin and thyroid markers are standard parts of a hormonal workup because both axes influence the gonadal one. DHEA-S captures part of the adrenal contribution, and adrenal androgens also include 11-oxygenated forms such as 11-keto-testosterone 4.
Metabolic markers belong in the same reading. Fasting glucose, insulin, HbA1c, triglycerides and liver enzymes all track with the conditions that shift SHBG, so they frequently explain a pattern that hormones alone do not. A complete blood count with hematocrit, ferritin and vitamin D round out the picture that a clinician reviews.
This is the logic behind testing broadly rather than in isolation. FitScript's membership covers 150+ biomarkers tested per year, and Atlas, FitScript's AI health advisor, reads a hormone line in the context of the carrier proteins, pituitary signals and metabolic markers drawn at the same time.
Work through it in a fixed order and most of the confusion disappears. Start with the analyte name and identify which fraction it is, total, free or bioavailable. Then check the unit, because ng/dL, nmol/L and pg/mL are not comparable digits. Then look for a method suffix, since a direct free testosterone and a dialysis free testosterone are different measurements wearing similar names 3.
Next, read the reference interval printed beside your result rather than one you found elsewhere, and check whether it is sex and age specific. Confirm the collection time if it is recorded, because an afternoon draw changes how a borderline value should be read 1. If a free or bioavailable value appears, look for SHBG and albumin nearby and see whether the free line is flagged as calculated.
Finally, place the result in a sequence. One value is a point, two or three values at the same laboratory are a direction. If your report carries a flag, note it and bring it to a clinician rather than discounting it, even when the rest of the page looks unremarkable.
Any flagged result is worth discussing, and so is an unflagged result that sits at odds with how you feel. The clearest prompts are a low morning total testosterone confirmed on a second sample, a mismatch between total and free with an unusual SHBG, a value in women that is persistently above the reference interval, or any result alongside symptoms such as persistent fatigue, low libido, mood change, loss of muscle mass, menstrual irregularity or unexplained hair changes.
A clinician will look at the whole panel, your history, your medications and the pituitary markers before forming any view, and will decide whether repeat or additional testing is needed. If any therapy is ever considered, a licensed provider evaluates whether it is appropriate for you, selects it and supervises it. Nothing about that decision can be made from a single line on a report, and this guide deliberately does not cover it.
This article is educational and is not medical advice. Discuss your own results, and any therapy you are considering, with a clinician or licensed provider.
For the practical side of getting tested, including timing and preparation, see how to test testosterone levels, and for one of the more common questions about nutrient status and hormone levels, see does vitamin d affect testosterone.
Yes, in almost every case. 'Testosterone, Serum' simply names the sample type and refers to the total measurement, bound and unbound hormone counted together. If a laboratory reports a separate free or bioavailable value, it will be printed on its own line with its own unit, usually pg/mL or pmol/L for free testosterone.
It means the unbound fraction was estimated with a direct analog immunoassay in a single step, rather than separated by equilibrium dialysis or calculated from total testosterone, SHBG and albumin.
Because SHBG is the main carrier protein for testosterone and is a required input for any calculated free or bioavailable value. Many panels add it automatically. It also explains the most common mismatch readers notice, where a normal total sits next to a low free value because SHBG is high.
Multiply the nmol/L figure by about 28.8 to get ng/dL, or divide ng/dL by about 28.8 to go the other way. For free testosterone the units are different again, with 1 pg/mL equalling roughly 3.47 pmol/L. Always check which fraction the unit belongs to before converting anything.
It is the free fraction plus the loosely albumin bound fraction, reported as one number in ng/dL or nmol/L. The idea is that albumin releases testosterone readily as blood passes through tissue, so that portion behaves more like accessible hormone than the tightly SHBG bound portion does.
Reference intervals are set by each laboratory for its own assay, population and calibration, and they vary by age and sex. Compare your value against the interval printed on your own report rather than one taken from elsewhere.
Not always. Because most circulating testosterone is protein bound, a normal total can sit alongside a lower free fraction when SHBG is high, and the reverse pattern occurs when SHBG is low. That is why clinicians often look at total, free and SHBG together rather than at one line alone.
It is a calculated ratio, total testosterone in nmol/L divided by SHBG in nmol/L and multiplied by one hundred. It is not a concentration and it is not a substitute for a measured free testosterone. Its usefulness depends on the population and the assay behind the two inputs.
Testosterone follows a daily rhythm that peaks in the morning, and clinical guidance specifies a morning sample in the fasting state, with a low result confirmed on a separate day. Avoid testing during acute illness or straight after an unusually hard training block, and keep conditions consistent between draws.