Dihydrotestosterone (DHT), Free, LC/MS/Dialysis
The Free DHT test measures the unbound, biologically available fraction of dihydrotestosterone by equilibrium dialysis with LC-MS/MS. As the most potent androgen and the 5-alpha-reduced product of testosterone, DHT drives androgenetic alopecia, hirsutism, and prostatic growth.
3
Biomarkers
Blood (serum)
Sample
4–9 business days
Turnaround
No
Fasting
What is the Free DHT test?
The Dihydrotestosterone (DHT), Free, LC/MS/Dialysis test quantifies the unbound, biologically available fraction of the most potent human androgen, using physical equilibrium dialysis to isolate free hormone followed by liquid chromatography–tandem mass spectrometry for specific, interference-resistant quantitation. DHT is the 5-alpha-reduced product of testosterone and the principal androgen acting at the hair follicle, sebaceous gland, prostate, and external genitalia. Because the free fraction is what diffuses into these tissues and occupies the androgen receptor, measuring it directly gives the clinician a reading tied to androgen action rather than to total circulating mass, which is dominated by protein-bound hormone that is not immediately available.
In the diagnostic landscape this is a methodologically distinct assay, not a more precise version of a routine DHT order. A standard total DHT — particularly by immunoassay — reports the whole bound-plus-free pool and is vulnerable both to analytic cross-reactivity and to distortion by sex hormone-binding globulin. The dialysis-plus-mass-spectrometry free measurement sidesteps both problems, so it is reserved for questions where tissue androgen availability, not gross secretion, is the issue: evaluating androgen-dependent conditions in the setting of abnormal SHBG, resolving discordance between symptoms and a normal total result, and following the pharmacodynamic response to 5-alpha-reductase inhibition. Practitioners order it to clarify, monitor, and quantify androgen exposure, usually alongside testosterone and SHBG, rather than as a stand-alone screen.
What does the Free DHT test measure?
Dihydrotestosterone is the 5-alpha-reduced metabolite of testosterone and the most potent endogenous androgen, binding the androgen receptor with roughly two- to threefold greater affinity and dissociating more slowly than its precursor. It is generated largely in peripheral target tissues — skin, hair follicle, prostate, genital tissue — by the type 1 and type 2 isoforms of 5-alpha-reductase, so circulating concentrations partly reflect tissue conversion rather than gonadal secretion alone. In plasma the bulk of DHT travels bound to sex hormone-binding globulin and albumin; only the small unbound fraction is immediately available to diffuse into cells and engage the receptor. Equilibrium dialysis physically separates that free fraction before quantitation, which is why the measured free concentration tracks biological availability more closely than a total value does.
Free DHT reflects the androgen fraction actually available to receptor-bearing tissue and is the quantity most relevant to androgen-driven phenotypes such as androgenetic alopecia, hirsutism, and prostatic growth. Because it is measured on the unbound pool, it is far less distorted by shifts in sex hormone-binding globulin than total DHT, and it provides a more interpretable readout when monitoring the pharmacodynamic effect of 5-alpha-reductase inhibitors, in whom total and free DHT both fall but the free value better represents residual tissue exposure.
Total DHT is the sum of protein-bound and free dihydrotestosterone and is quantified here by liquid chromatography–tandem mass spectrometry, which resolves DHT from testosterone and other structurally similar steroids that cross-react in older immunoassays. Because most DHT is SHBG-bound, the total value moves with binding-protein concentration and can misrepresent tissue androgen availability when SHBG is high (ageing, thyroid excess, hepatic disease) or low (obesity, insulin resistance, exogenous androgen).
Total DHT by mass spectrometry is the specific, interference-resistant measurement of the whole circulating pool and the input from which the free fraction is derived during dialysis. It is informative for confirming 5-alpha-reductase activity and for documenting suppression on inhibitor therapy, but it should be read together with the free value and SHBG rather than alone.
The percent-free value is the ratio of dialysable (free) DHT to total DHT, expressed as a percentage. It summarises how binding-protein status partitions the hormone between bound and available pools: a rise in SHBG lowers the free fraction even when total DHT is unchanged, and a fall in SHBG raises it. The ratio is therefore a useful internal check on whether a given total value over- or under-represents biologically active androgen.
A derived marker rather than a direct measurement, the percent-free fraction helps the clinician judge whether an apparently normal or abnormal total DHT is explained by binding-protein shifts. It is most useful at the extremes of SHBG and when free and total results appear discordant.
Why is the Free DHT test ordered?
- Men with progressive androgenetic alopecia being evaluated before or during 5-alpha-reductase inhibitor therapy, where residual free DHT reflects ongoing follicular androgen exposure
- Clinicians monitoring finasteride or dutasteride pharmacodynamics, where confirming adequate DHT suppression informs dose and adherence decisions
- Women undergoing work-up of hirsutism or androgenic alopecia in whom SHBG is altered and total androgens are difficult to interpret
- Evaluation of benign prostatic hyperplasia or related lower urinary tract symptoms where tissue androgen drive is under consideration
- Patients with suspected or confirmed 5-alpha-reductase type 2 deficiency, or ambiguous virilisation, interpreted with the testosterone-to-DHT ratio
- Men and women with discordance between androgenic symptoms and a normal or borderline total DHT, where the free fraction may explain the clinical picture
- Assessment of androgen status in conditions with markedly abnormal SHBG (obesity, insulin resistance, thyroid dysfunction, hepatic disease) that invalidate total DHT interpretation
- Specialist monitoring of androgen-sensitive conditions during hormone therapy, interpreted alongside testosterone, SHBG, and oestradiol
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
4–9 business days
Collection notes
Phlebotomy at a LabCorp draw site (or Access Medical Laboratories depending on routing). A morning draw is preferred given diurnal variation in the androgen axis. Record any 5-alpha-reductase inhibitor, testosterone, or topical androgen use on the requisition, as these materially alter interpretation.
Specimen requirements
Serum collected in a plain or gel-separator tube; separate promptly and refrigerate or freeze per the performing laboratory's instructions, as the dialysis and LC-MS/MS workflow has defined handling and stability requirements. Note the performing laboratory and method for serial comparability; free DHT results are not transferable between methods.
What can affect Free DHT results?
These agents block conversion of testosterone to DHT; finasteride (type 2) lowers serum DHT substantially and dutasteride (dual-isoform) suppresses it further, so both total and free DHT fall sharply and must be interpreted against the therapeutic intent.
SHBG governs the bound-to-free partition; high SHBG (ageing, hyperthyroidism, hepatic disease) lowers the free fraction while low SHBG (obesity, insulin resistance, exogenous androgen) raises it, shifting free DHT independently of total production.
Supplying additional substrate for 5-alpha-reductase increases DHT generation, and the accompanying fall in SHBG further raises the free fraction, so free DHT can rise disproportionately during androgen therapy.
Transdermal androgens and inadvertent contact exposure can raise measured DHT; a careful exposure history is needed because local preparations may elevate systemic levels unpredictably.
These states suppress SHBG, which raises the free fraction, while altered peripheral steroid metabolism and aromatisation change the testosterone-to-DHT relationship, so results require metabolic context.
Free DHT depends on dialysis temperature, buffer, and dilution as well as the LC-MS/MS calibration; results from dialysis-based mass spectrometry are not interchangeable with calculated free values or immunoassays, and serial comparison should stay within one method.
What do Free DHT results mean?
Elevated
Raised free DHT indicates increased androgen availability at target tissue. Common contexts include exogenous or anabolic androgen use, states of low SHBG that raise the free fraction, and increased 5-alpha-reductase conversion. Elevated free DHT with androgenic symptoms (alopecia, hirsutism, acne, prostatic symptoms) supports an androgen-driven process; correlate with total DHT, testosterone, and SHBG to distinguish increased production from a binding-protein shift.
Normal
A free DHT within the method-specific reference interval does not exclude an androgen-mediated condition, since target-tissue sensitivity and local follicular 5-alpha-reductase activity vary and are not captured by circulating levels. Conversely, a normal total DHT with altered SHBG may conceal an abnormal free fraction, which is precisely the scenario the dialysis method is designed to clarify. Interpret in light of phenotype, testosterone, and SHBG.
Reduced
Low free DHT is the expected and desired finding during 5-alpha-reductase inhibitor therapy and confirms pharmacodynamic effect. Outside treatment, low values may reflect 5-alpha-reductase deficiency (with a high testosterone-to-DHT ratio), hypogonadism, or high SHBG reducing the available fraction. A low free value despite adequate testosterone points toward impaired conversion or increased binding.
Note: This is a method-specific measurement: free DHT by equilibrium dialysis with LC-MS/MS is not equivalent to a calculated free value, an immunoassay result, or a routine total DHT, and the numbers should not be compared across methods. Reference intervals are age- and sex-dependent and narrow; the free fraction is small, so pre-analytic and dialysis conditions matter. Always interpret alongside testosterone and SHBG, and read suppression on inhibitor therapy as an expected effect rather than a deficiency.
Frequently asked questions
A total DHT reports the whole circulating pool, most of which is protein-bound and not available to tissue, and it can be distorted by sex hormone-binding globulin or by immunoassay cross-reactivity. The free test uses equilibrium dialysis to isolate the unbound fraction and LC-MS/MS to quantify it specifically, so it reflects biologically available androgen. The two are methodologically distinct measurements, not duplicates.
How to access the Free DHT test
The Free DHT reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Bhasin S, et al. Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. (verify citation/PMID). (2018)
- Rosner W, et al. Position statement: utility, limitations, and pitfalls in measuring testosterone — mass spectrometry and the measurement of sex steroids. J Clin Endocrinol Metab. (verify citation/PMID). (2007)
- Andriole GL, et al. Effect of dutasteride on the risk of prostate cancer (REDUCE) — DHT suppression by dual 5-alpha-reductase inhibition. N Engl J Med. (verify citation/PMID). (2010)
- Kaufman KD, et al. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol. (verify citation/PMID). (1998)
- Swerdloff RS, et al. Dihydrotestosterone: biochemistry, physiology, and clinical implications of elevated blood levels. Endocr Rev. (verify citation/PMID). (2017)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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