Serum androgen levels reflect a broad sweep of biological activity, from reproductive function and body composition to bone density, mood, and metabolic health. Testosterone is the androgen most commonly tested, but related hormones like dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), and its sulfated form DHEA-S also carry diagnostic information depending on the clinical question. A single testosterone reading is rarely meaningful on its own; it gains significance in the context of when the blood was drawn, how it was measured, and the person’s sex, age, symptoms, and binding-protein levels.
Free Versus Total Testosterone
Most testosterone in the blood is bound to proteins, primarily sex hormone-binding globulin (SHBG) and albumin. Only a small fraction circulates “free,” meaning unattached to any protein. This distinction matters because the tissue exposure your body experiences depends on the balance between free and total testosterone, which is set by how much SHBG and albumin are present.1PubMed Central. Role of sex hormone-binding globulin in the free hormone hypothesis and the relevance of free testosterone in androgen physiology SHBG-bound testosterone is effectively locked away from entering tissues and triggering androgen effects.2Scientific Reports. Sex hormone-binding globulin regulation of androgen bioactivity in vivo: validation of the free hormone hypothesis
This is why two people can have the same total testosterone number yet experience very different androgen effects. If your SHBG is high, say from hyperthyroidism or estrogen-containing medications, your total testosterone may look normal or even elevated while your free testosterone stays unremarkable.3Endocrine Abstracts. A surprising diagnosis in a man with high testosterone levels Conversely, low SHBG (common with obesity or insulin resistance) can make total testosterone look deceptively low while the biologically active fraction is adequate. A complete picture usually requires measuring both total and free testosterone, or at least total testosterone alongside SHBG so that free testosterone can be calculated.
Why the Time of Your Blood Draw Matters
Testosterone follows a circadian rhythm. Levels peak in the early morning and dip through the afternoon. In younger men, the difference is substantial: levels measured at 4 p.m. can be roughly 20 to 25 percent lower than those measured at 8 a.m.4PubMed Central. The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men That gap narrows with age, shrinking to about 10 percent by age 70, but it never disappears entirely. The early-morning rise appears to be driven by an internal circadian clock rather than sleep itself; studies separating the effects of sleep stages from time of day found that testosterone climbed in the early-morning hours regardless of whether the subject was asleep or awake.5The Journal of Clinical Endocrinology & Metabolism. Circadian Rhythm of Serum Testosterone and Its Relation to Sleep: Comparison with the Variation in Serum Luteinizing Hormone, Prolactin, and Cortisol in Normal Men
The practical consequence is that an afternoon blood draw can push someone below the clinical cutoff for low testosterone when their morning level would have been perfectly normal. In one study, 17 men whose afternoon readings fell below 300 ng/dL had entirely normal results on every morning measurement.4PubMed Central. The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men Guidelines therefore recommend drawing testosterone before noon, and ideally before 10 a.m., with a repeat confirmatory sample on a separate day.
What Low Androgens Indicate in Men
Male hypogonadism, the clinical term for persistently low testosterone accompanied by symptoms, is diagnosed when lab findings and clinical signs align. Symptoms typically include fatigue, reduced libido, erectile difficulty, depressed mood, and loss of muscle mass.6PubMed Central. Adult Male Hypogonadism: A Laboratory Medicine Perspective on Its Diagnosis and Management A low number alone, without symptoms, does not automatically warrant treatment, a point that can get lost in the direct-to-consumer testosterone marketing landscape.
The cause of low testosterone also matters. “Primary” hypogonadism means the testes themselves are failing, which typically shows up as low testosterone with elevated LH and FSH (the pituitary hormones trying to stimulate the testes harder). “Secondary” hypogonadism means the problem is higher up, at the pituitary or hypothalamus, and both testosterone and the signaling hormones are low. This distinction shapes treatment: secondary causes may include pituitary tumors, medications, or severe illness, each needing a different approach. Some researchers have argued for moving beyond population-based reference ranges toward evidence-based action thresholds that better predict who will benefit from treatment.7PubMed Central. Serum testosterone levels in male hypogonadism: Why and when to check-A review
Low testosterone in men is linked to a cluster of metabolic problems. The association with visceral fat accumulation and insulin resistance is well established, and low levels are tied to a higher prevalence of metabolic syndrome components.8Nature Reviews Endocrinology. Testosterone deficiency, insulin resistance and the metabolic syndrome Bone mineral density also declines as testosterone drops with age, contributing to fracture risk in older men.9PubMed Central. Testosterone and Bone Health in Men: A Narrative Review Both testosterone and estradiol, which testosterone is partly converted into, appear to influence bone independently, and both decline matters.10PubMed. Sex hormone levels as determinants of bone mineral density and osteoporosis in Vietnamese women and men
The Age-Related Decline
Testosterone does not fall off a cliff at some birthday. It drifts downward gradually, and the rate of decline is steeper than cross-sectional snapshots suggest. The Massachusetts Male Aging Study, which followed men over time, found total testosterone declined at about 1.6 percent per year longitudinally, while the biologically available fraction dropped at 2 to 3 percent per year.11The Journal of Clinical Endocrinology & Metabolism. Age Trends in the Level of Serum Testosterone and Other Hormones in Middle-Aged Men: Longitudinal Results from the Massachusetts Male Aging Study The Baltimore Longitudinal Study of Aging confirmed a similar age-invariant decline in both total and free testosterone.12The Journal of Clinical Endocrinology & Metabolism. Longitudinal Effects of Aging on Serum Total and Free Testosterone Levels in Healthy Men
What makes the Massachusetts data particularly interesting is the finding that longitudinal declines were steeper than cross-sectional ones. The researchers suggested that declining health itself may accelerate hormone loss, creating a feedback loop in which lower testosterone worsens metabolic health, which in turn pushes testosterone lower.11The Journal of Clinical Endocrinology & Metabolism. Age Trends in the Level of Serum Testosterone and Other Hormones in Middle-Aged Men: Longitudinal Results from the Massachusetts Male Aging Study The aging process also affects the signaling architecture: age acts on both the hypothalamus-pituitary pathway and the testosterone-producing Leydig cells in the testes, reducing production from both ends.13PubMed Central. Age-related testosterone decline: mechanisms and intervention strategies
What Androgen Levels Indicate in Women
Androgens in women come from two sources: the ovaries and the adrenal glands. The adrenal reticularis produces the bulk of DHEA and DHEA-S, which are weaker androgens often described as precursors.14PubMed Central. Regulation of the adrenal androgen biosynthesis The ovaries contribute testosterone and androstenedione more directly. Because women have much lower androgen levels than men, even small shifts carry outsized clinical weight.
The most common reason women get androgen levels checked is suspected polycystic ovary syndrome (PCOS). Elevated testosterone is one of the hallmarks, and serum total testosterone performs reasonably well as a diagnostic marker, with pooled sensitivity around 74 percent and specificity around 86 percent in a meta-analysis spanning over 2,000 participants.15Human Reproduction Update. Evaluating the diagnostic accuracy of androgen measurement in polycystic ovary syndrome: a systematic review and diagnostic meta-analysis to inform evidence-based guidelines DHEA-S, by contrast, is a less reliable PCOS marker, with lower specificity. One study using age-adjusted norms found true DHEA-S elevation in only about 8 percent of women with PCOS, casting doubt on its routine usefulness for diagnosing the condition.16PubMed. Is it useful to measure DHEAS levels in PCOS? That said, when DHEA-S is elevated, it does tend to track with higher testosterone and androstenedione levels.17PubMed Central. Increased Prevalence of Elevated DHEAS in PCOS Women with Non-Classic (B or C) Phenotypes: A Retrospective Analysis in Patients Aged 20 to 29 Years
On the other end of the spectrum, androgen deficiency in women is an underrecognized problem. After menopause, both ovarian and adrenal androgen production decline, which can reduce libido, dampen mood, and affect the health of genital and urinary tissues.18PubMed Central. Changes of androgens levels in menopausal women A low free testosterone level in a woman reporting reduced desire, diminished well-being, or persistent low mood raises the possibility of what has been termed the female androgen insufficiency syndrome.19Human Reproduction Update. Androgen insufficiency in women: diagnostic and therapeutic implications Currently, hypoactive sexual desire disorder remains the only evidence-based indication for testosterone therapy in women, and the doses used are a fraction of what men receive.
Lifestyle Factors That Move the Numbers
Serum androgen levels respond to everyday conditions, which means a single reading can reflect a temporary state rather than a lasting problem. Sleep is one of the bigger levers. A meta-analysis found that total sleep deprivation (staying awake for 24 hours or more) significantly lowered testosterone, while partial sleep restriction had a smaller and statistically nonsignificant effect.20Sleep Medicine. Effect of partial and total sleep deprivation on serum testosterone in healthy males: a systematic review and meta-analysis A controlled study in young healthy men found that even six weeks of modest sleep restriction did not produce the dramatic testosterone crash that popular media sometimes implies.21PubMed Central. Sleep restriction and testosterone concentrations in young healthy males: randomized controlled studies of acute and chronic short sleep The upshot: a truly terrible night or several days of no sleep will depress your reading, but moderate short sleep over a few weeks is unlikely to slash testosterone by the amounts you might fear.
Energy availability is a much more powerful suppressor. When calorie intake falls far short of expenditure, testosterone can plummet. In a study of men undergoing eight days of severe energy deficit combined with intense physical activity, testosterone dropped by about 45 percent.22PubMed. Effects of dietary protein content on IGF-I, testosterone, and body composition during 8 days of severe energy deficit and arduous physical activity Similar patterns have been documented in military training settings, where Marines who developed low testosterone after a short-term severe deficit also lost more lean mass than those whose levels held up.23PubMed Central. Testosterone status following short-term, severe energy deficit is associated with fat-free mass loss in U.S. Marines Extreme endurance training can produce a similar picture, sometimes called “exercise-hypogonadal male condition,” which appears to be a transient, functional suppression tied to low energy availability or excessive training load rather than permanent damage.24PubMed Central. Hypogonadism in Exercising Males: Dysfunction or Adaptive-Regulatory Adjustment? In these cases, the low reading is informative but not the same as chronic hypogonadism. It reflects a body under acute stress, and levels typically recover once energy balance is restored.
Medications That Alter Readings
Several commonly prescribed drugs shift androgen levels enough to confuse a diagnosis if the clinician is not looking for them. Glucocorticoids are among the most impactful. In a study of older men on chronic glucocorticoid therapy, testosterone averaged about 211 ng/dL, compared to roughly 449 ng/dL in matched controls not on steroids, a reduction of more than half.25PubMed. Reduction of serum testosterone levels during chronic glucocorticoid therapy The mechanism appears to involve suppression of the hypothalamic signal that drives testosterone production. Opioids, certain antidepressants, and antiepileptic drugs can also lower testosterone through various pathways, making a medication review an essential part of interpreting any androgen panel.
Thyroid disease provides another instructive example. Hyperthyroidism can raise total testosterone by boosting SHBG production in the liver, making total testosterone look elevated while free testosterone remains normal. The effect usually reverses once thyroid function is corrected.3Endocrine Abstracts. A surprising diagnosis in a man with high testosterone levels Without checking free testosterone or SHBG, a clinician might chase the wrong diagnosis entirely.
Mood, Cognition, and Behavior
Androgen levels are tied to psychological well-being in ways that go beyond the stereotypical “aggression hormone” framing. In men, low testosterone has been linked to depressive symptoms spanning a wide range, from general fatigue and listlessness to more severe hopelessness and even suicidal ideation. Anxiety traits, from unfocused worry to phobic patterns, have also been connected to low testosterone.26PubMed. Testosterone, mood, behaviour and quality of life The relationship between testosterone and major depression appears fairly consistent, with depressed men tending to have lower levels than non-depressed controls. The picture is murkier for bipolar disorder, where results are mixed.27PubMed. Association between testosterone levels and mood disorders: A minireview
Testosterone replacement in men with confirmed deficiency has shown improvements in depression scores and aging-related symptoms, and there is evidence of cognitive improvement in men who already had cognitive impairment at baseline.28PubMed Central. Effect of Testosterone Replacement Therapy on Cognitive Performance and Depression in Men with Testosterone Deficiency Syndrome These benefits were seen in men whose testosterone was genuinely low and who had clear symptoms before treatment. This does not mean that supplementing already-normal levels will sharpen your thinking or lift your mood; the evidence supports restoration, not enhancement.
Why the Same Level Affects People Differently
One of the more underappreciated factors in interpreting androgen levels is androgen receptor sensitivity. The androgen receptor gene contains a stretch of repeating DNA called the CAG repeat, and its length varies between individuals. Shorter repeats make the receptor more sensitive to testosterone, meaning a given testosterone level has a greater biological effect. Longer repeats do the opposite.29PubMed Central. Androgen receptor (AR) gene CAG trinucleotide repeat length associated with body composition measures in non-syndromic obese, non-obese and Prader-Willi syndrome individuals This helps explain why some men with borderline-low testosterone feel fine while others with the same number experience significant symptoms.
The CAG repeat length even modifies how testosterone interacts with metabolic health. In one study, the relationship between testosterone and insulin resistance flipped depending on CAG length: in men with longer repeats, rising testosterone improved insulin sensitivity, while in men with shorter repeats (below about 23), the same testosterone increase had the opposite effect.30PubMed. Androgen receptor CAG repeat length polymorphism modifies the impact of testosterone on insulin sensitivity in men This finding underscores why a testosterone number without clinical context is incomplete. Two patients with identical lab results may warrant different management based on their receptor genetics and their symptom profiles.
How the Testosterone Was Measured Matters More Than You Think
Not all testosterone assays are created equal, and the measurement method can meaningfully affect your result. Immunoassays, the automated platforms used in most hospital and commercial laboratories, are fast and cheap, but their accuracy deteriorates at low testosterone concentrations, exactly the range that matters most when evaluating women, children, or men suspected of hypogonadism. One comparison found that a widely used immunoassay platform produced results about 20 percent lower than mass spectrometry and showed minimal correlation with the reference method below 100 ng/dL.31PubMed Central. Using mass spectrometry to overcome the longstanding inaccuracy of a commercially-available clinical testosterone immunoassay
A broader comparison of six different immunoassay methods against liquid chromatography-tandem mass spectrometry (LC-MS/MS, considered the gold standard) found that some platforms consistently read low while others read high. One platform was biased downward by an average of 90 ng/dL, and another was biased upward by about 99 ng/dL across the adult male range.32The Journal of Clinical Endocrinology & Metabolism. Measurement of Total Serum Testosterone in Adult Men: Comparison of Current Laboratory Methods Versus Liquid Chromatography-Tandem Mass Spectrometry For distinguishing normal from low in adult men, most automated immunoassays still work well enough if the lab has established its own reference range. But for precise measurement in women or for tracking small changes over time, mass spectrometry is the better tool.
This matters if you are comparing results between labs or tracking your levels over time using different providers. A switch from one assay platform to another can produce an apparent change that is entirely methodological, not biological. If you are monitoring testosterone, try to use the same laboratory and the same method each time. The push for mass spectrometry-based assays has been gaining ground over the past decade, and major endocrinology journals now require mass spectrometry for sex steroid measurements in research submissions.33The Journal of Clinical Endocrinology & Metabolism. Requirement for Mass Spectrometry Sex Steroid Assays in the Journal of Clinical Endocrinology and Metabolism
Testosterone’s Downstream Hormones
Testosterone does not act alone. Much of its biological work is done after it is converted into other hormones, mainly DHT and estradiol. DHT is a more potent androgen that drives effects in the prostate, skin, and hair follicles. Estradiol, an estrogen, is produced from testosterone via the aromatase enzyme, particularly in fat tissue. In the Testosterone Trials, changes in estradiol were the strongest predictor of improvements in bone density and were also associated with increases in hemoglobin and sexual desire. Meanwhile, greater increases in estradiol tracked with larger drops in HDL cholesterol.34PubMed Central. Relation of Testosterone, Dihydrotestosterone, and Estradiol With Changes in Outcomes Measures in the Testosterone Trials This means that interpreting androgen levels in isolation, without considering how they are being converted, misses part of the picture.
The feedback loop governing all of this runs through the hypothalamus and pituitary. Rising testosterone inhibits the hypothalamic release of GnRH, which in turn dials back pituitary LH and FSH secretion, slowing further testosterone production. The feedback signal does not even act on GnRH neurons directly; it works through intermediate neurons called kisspeptin neurons in the hypothalamus.35PubMed Central. The role of testosterone, the androgen receptor, and hypothalamic-pituitary–gonadal axis in depression in ageing Men This elegant self-regulation is why exogenous testosterone (injections, gels, or pellets) suppresses your own production: the pituitary sees enough testosterone in the blood and stops sending the signal to make more. It is also why monitoring LH and FSH alongside testosterone provides a clearer diagnostic picture.
Polycythemia and Cardiovascular Monitoring During Testosterone Therapy
One of the more concrete risks flagged by androgen levels during testosterone replacement therapy is polycythemia, an increase in red blood cell concentration. Testosterone stimulates red blood cell production, which is why hemoglobin often rises during treatment. When hematocrit climbs too high, blood becomes thicker, and the risk of clotting events goes up. In a large analysis, men who developed polycythemia while on testosterone therapy had a higher rate of major cardiovascular events and blood clots compared to men whose hematocrit stayed normal, with about a 35 percent increase in odds.36PubMed Central. Secondary Polycythemia in Men Receiving Testosterone Therapy Increases Risk of Major Adverse Cardiovascular Events and Venous Thromboembolism in the First Year of Therapy This is why periodic blood count monitoring is standard practice during testosterone therapy, and why an unexpectedly high hematocrit can prompt dose adjustments or temporary treatment pauses. For women considering androgen levels in the context of bone health, the data also suggests a positive link between testosterone and bone mineral density at the lumbar spine in postmenopausal women, with the relationship being nonlinear.37PubMed Central. Association between Serum Total Testosterone Level and Bone Mineral Density in Middle-Aged Postmenopausal Women