There is no single number that means "low." The Endocrine Society's diagnostic standard is symptoms plus unequivocally and consistently low concentrations — not a threshold you cross.[1] And for a substantial group of men, the total testosterone figure at the top of the report is the least useful line on it, because it counts hormone their tissue cannot reach.
What the three numbers on a good panel mean
Total testosterone. Everything in circulation, bound and unbound together. It is the recommended initial test, and for many men it settles the question on its own.[1]
SHBG. Sex hormone-binding globulin binds testosterone tightly. Testosterone bound to SHBG is, for practical purposes, out of play. SHBG is not a footnote on the panel — it is the variable that determines whether total testosterone means what it appears to mean.
Free testosterone. The fraction not bound to SHBG. This is the number that tracks with what tissue can actually use, and it is the one a basic panel most often omits.
The distribution between these fractions is more complex than the classic textbook account, and a 2017 reappraisal in Endocrine Reviews revised the model of how testosterone binds in circulation.[2] The practical consequence for reading your own results is unchanged and simple: total and free can tell different stories about the same man.
When your clinician should be looking at free testosterone
The guideline is specific. Obtain a free testosterone concentration when total testosterone is near the lower limit of normal, or when the man has a condition that alters SHBG.[1]
Things that move SHBG are common: age, thyroid disease, liver disease, obesity, diabetes, and several medications. If any apply to you, a total testosterone reading in isolation is a weaker piece of evidence than it looks.
Why "within range" is a weaker reassurance than it sounds
Reference ranges describe a population. They are wide, they are drawn from morning samples, and they vary between laboratories and assays — which is why the guideline emphasises an accurate and reliable assay rather than naming a universal cut-off.[1]
Two men can both sit inside the range and be in entirely different clinical situations. The one whose SHBG has risen may have meaningfully less usable hormone than his total suggests, and that gap widens with age: the European Male Ageing Study measured total testosterone falling about 0.4% a year against free testosterone falling about 1.3%.[4]
This is the single most common way a result gets misread — as reassurance, when the fraction that matters was never measured. The mechanism is set out in free vs total testosterone.
What a result cannot tell you
A number cannot tell you whether your symptoms come from testosterone. That is the honest limit of the panel, and it cuts against enthusiasm in both directions.
Low reading with no symptoms is not a diagnosis under the guideline.[1] Symptoms with a normal free testosterone point somewhere else — sleep, thyroid, mood, alcohol, medication — and those causes are common and treatable in their own right. The symptom articles in this hub, including brain fog and sleep, each cover what the trials found and what else produces the same picture.
Frequently asked questions
My total is normal but my free is low. Which one counts? Both are real measurements; they answer different questions. Free testosterone tracks the fraction available to tissue, which is why the guideline asks for it specifically when SHBG is likely to be distorting the total.[1] Interpretation belongs with your clinician alongside symptoms.
Why did two labs give me different numbers? Assays differ. This is precisely why the guideline specifies an accurate and reliable assay and recommends confirming a result rather than acting on one.[1] Where possible, keep repeat testing on the same assay.
Do I need LH and FSH? The guideline recommends further evaluation to establish the cause of a confirmed deficiency.[1] Pituitary hormones are part of how that question gets answered — they help distinguish a testicular cause from a signalling one.
Is there a target number for treatment? For men on therapy, the guideline suggests aiming at testosterone concentrations in the mid-normal range.[1] That is a treatment target, not a diagnostic threshold — a distinction worth keeping separate.
Getting the full picture measured
The panel that answers the question is total testosterone, free testosterone and SHBG together, drawn fasting in the morning, confirmed on a second draw, and read against your symptoms.
Keen connects you with a licensed clinical team for a telehealth consultation and lab review. If your testosterone is clinically low, treatment is Keen Testosterone Spray Rx — a once-daily topical spray powered by Hypospray® transdermal delivery.
Related reading: your first testosterone test and how much testosterone you lose with age.
References
4 sources
- Bhasin S, Brito JP, Cunningham GR, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2018;103(5):1715–1744. doi:10.1210/jc.2018-00229 · PMID 29562364
- Goldman AL, Bhasin S, Wu FCW, et al. A Reappraisal of Testosterone's Binding in Circulation: Physiological and Clinical Implications. Endocr Rev. 2017;38(4):302–324. doi:10.1210/er.2017-00025 · PMID 28673039
- Vermeulen A, Verdonck L, Kaufman JM. A critical evaluation of simple methods for the estimation of free testosterone in serum. J Clin Endocrinol Metab. 1999;84(10):3666–3672. doi:10.1210/jcem.84.10.6079 · PMID 10523012
- Wu FC, Tajar A, Pye SR, et al. Hypothalamic-pituitary-testicular axis disruptions in older men are differentially linked to age and modifiable risk factors: the European Male Aging Study. J Clin Endocrinol Metab. 2008;93(7):2737–2745. doi:10.1210/jc.2007-1972 · PMID 18270261
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