Understand how SHBG affects total and free testosterone, when clinicians consider extra testing, and why symptoms and test methods matter.
Total testosterone and free testosterone describe different aspects of circulating hormone, so their relationship can change how clinicians assess possible testosterone deficiency.
This article is for informational purposes only and is not medical advice. A qualified clinician should interpret individual results and make decisions about further testing or treatment.
Total testosterone measures the testosterone circulating in blood, including both protein-bound and unbound hormone. Sex hormone-binding globulin, usually shortened to SHBG, is a protein that binds testosterone. The word “total” describes what is included in the measurement rather than how much testosterone is unbound.
The European Association of Urology (EAU) guideline places morning total testosterone at the centre of the laboratory assessment for suspected late-onset hypogonadism. This is the clinical condition in which compatible symptoms or signs occur alongside consistently low testosterone. Total testosterone therefore has an established medical use rather than being a less useful version of a free-testosterone test.
Its interpretation still depends on what contributes to that total. The EAU guideline notes that total testosterone values may vary with SHBG. Understanding how bound and unbound measurements fit together helps explain why an additional measurement may sometimes add useful context.
The question is not simply whether total testosterone is a “good” test. It is whether that result adequately answers the clinical question in the circumstances being assessed.
Free testosterone is the unbound fraction of circulating testosterone. It is not a different hormone from total testosterone. Instead, it describes one component within the total measurement.
This gives the two tests different roles. Total testosterone captures the combined circulating amount, while free testosterone focuses on the portion not bound to proteins. According to the EAU guideline, evaluating free testosterone can improve diagnostic accuracy when SHBG may be altered.
However, the label “free testosterone” does not identify how the result was obtained. The guideline distinguishes between measurement methods and calculation.
The EAU guideline identifies equilibrium dialysis as the most accurate method for measuring free testosterone. Knowing whether this method was used gives the clinician important information about the result being interpreted.
“Measured” and “calculated” should therefore remain visible distinctions on a report or in a clinical discussion. They describe different ways of obtaining a value for the same unbound fraction.
The guideline describes calculation using total testosterone, SHBG and albumin as an alternative. In this approach, free testosterone is derived from those inputs rather than obtained through equilibrium dialysis.
That makes the calculation method part of the interpretation. A useful discussion includes the underlying measurements rather than treating the final calculated number as unrelated to them. Testostra’s explanation of the inputs behind a calculated result provides further context for this distinction.
The EAU guideline advises against direct free-testosterone estimates from available immunoassays because it considers them inaccurate. A laboratory result labelled “free testosterone” should not automatically be assumed to have the same reliability as equilibrium dialysis or an appropriate calculation.
The practical question is specific: how was this free-testosterone value obtained?
SHBG helps explain why total and free testosterone may not tell the same story. Because it binds circulating testosterone, a change in SHBG can change the relationship between the total amount and the unbound fraction.
The EAU guideline strongly recommends measuring SHBG and calculating free testosterone when a condition associated with altered SHBG is present. This is a targeted use of additional testing rather than a recommendation that every man needs every measurement.
With higher SHBG, more testosterone can be bound. A total value that appears reassuring may therefore need the additional context of free testosterone.
The EAU guideline lists ageing, hyperthyroidism and hepatic disease among factors associated with higher SHBG. Hepatic disease means disease affecting the liver. The guideline also lists smoking, HIV and certain medicines.
These circumstances help explain why clinicians may look beyond total testosterone. The total measurement includes bound hormone, so it does not separately identify how much is unbound. Free-testosterone assessment addresses that narrower question.
The reverse pattern can also matter. Lower SHBG can make total testosterone appear low while free testosterone remains normal.
A 2026 article in the Journal of Clinical Endocrinology & Metabolism specifically describes this pattern in association with obesity, diabetes and insulin resistance. The article discusses how low SHBG can produce spuriously low total testosterone despite a normal free-testosterone value.
The EAU guideline also lists obesity and insulin resistance among factors associated with lower SHBG. Other listed associations include type 2 diabetes or metabolic syndrome, hypothyroidism and some medicines.
These are associations rather than explanations for an individual result. Neither a health condition nor a medicine should be assumed to account for a particular SHBG value without clinical assessment.
Together, the two patterns show why “Which testosterone number matters more?” is often the wrong starting question. A better question is whether SHBG changes the meaning of the total result enough to make free-testosterone assessment useful.
Ageing can make the distinction between total and free testosterone more relevant. The EAU guideline cites European Male Ageing Study estimates of a 0.4% annual decline in total testosterone and a 1.3% annual decline in free testosterone.
Those figures describe study estimates rather than a yearly timetable for every man. Their value here is that the two measurements did not change at the same estimated rate.
The guideline also lists ageing among the circumstances associated with higher SHBG. That provides a reason to consider protein binding when interpreting testosterone results in older men rather than assuming total testosterone tells the whole story.
At the same time, the EAU describes healthy ageing as being associated with only a small and gradual testosterone decline. It identifies obesity and other health conditions as important contributors to functional hypogonadism.
The clinical picture is therefore broader than age alone. The guideline notes that free-testosterone evaluation can be particularly helpful in symptomatic older men with obesity. This brings the comparison back to the combination of symptoms and health context rather than an assumption that getting older necessarily means having testosterone deficiency.
Total and free testosterone are not competing treatments. They are measurements that can contribute to the assessment before a clinician decides whether testosterone replacement therapy, or TRT, is appropriate.
The EAU framework combines compatible symptoms or signs with consistently low testosterone. It also notes that symptoms are not specific to hypogonadism. A low laboratory value or a symptom by itself does not establish the diagnosis.
The guideline recommends morning total-testosterone testing while fasting and using a reliable assay. It calls for confirmation on at least two occasions and repeat measurement of a low result before testosterone therapy begins.
These requirements concern the quality and consistency of the evidence used for a decision. Adding free testosterone does not remove the need to establish whether the underlying findings are persistent and clinically relevant.
Acute illness is another consideration. The EAU guideline says acute disease can be associated with functional hypogonadism and advises against testosterone testing during acute illness. It also notes that non-fasting measurement can underestimate total testosterone in the circumstances it describes.
For interpretation, collection conditions belong alongside the result rather than being treated as an afterthought. A clinician can then decide whether a measurement reflects the situation that needs assessment or whether repeat testing is indicated.
The EAU guideline discusses 220 pmol/L (6.4 ng/dL) as a potentially useful free-testosterone threshold in the setting of altered SHBG. It explicitly describes the supporting evidence as limited.
That figure is not a universal cutoff or an automatic trigger for TRT. Its place is within the guideline’s broader diagnostic framework rather than outside it.
This distinction matters when comparing a laboratory report with a number found online. The clinical meaning depends on the testing method and the circumstances in which the threshold is being considered.
The evidence supports a focused discussion with a qualified clinician:
These questions clarify why another test might be useful without assuming that more testing always produces a better answer. The purpose is to resolve a specific uncertainty in the clinical picture.
For readers researching treatment, placing these biomarkers within a TRT discussion helps keep laboratory interpretation connected to clinical assessment. Neither measurement should be selected simply because it gives the more concerning or more reassuring result.
Total testosterone describes the circulating whole, while free testosterone clarifies its unbound component within the context of SHBG and the wider clinical assessment.
Ignoring SHBG can turn the comparison between total and free testosterone into a misleading choice between two numbers. Testostra’s evidence-led reporting puts biomarker terminology in clinical context so men researching their results can better understand what is being measured, without presenting that education as an individual diagnosis or treatment plan.
Testostra follows testosterone research, clinical guidance and emerging evidence without turning general information into personal treatment advice.
Send us a question, research idea or topic suggestion. Reader questions help shape future Testostra content.
Contact Testostra