Dihydrotestosterone, Free, Serum
The free DHT test measures the biologically active unbound fraction of dihydrotestosterone, the most potent naturally occurring androgen synthesised peripherally from testosterone by 5-alpha reductase. It is ordered to investigate suspected 5-alpha reductase deficiency, monitor biochemical response to inhibitor therapy, and evaluate unexplained androgen excess when testosterone is normal.
1
Biomarkers
Blood (serum)
Sample
3–5 business days
Turnaround
No
Fasting
What is the Free DHT test?
The Dihydrotestosterone, Free, Serum test measures the biologically active unbound fraction of the most potent endogenous androgen. It is not a routine screen but a specialised tool ordered when the clinician suspects a disorder of androgen metabolism or target-tissue response that total or free testosterone alone cannot explain. DHT is synthesised peripherally rather than secreted directly by the gonads, so its circulating concentration reflects both testosterone supply and local 5-alpha reductase activity. Practitioners turn to this assay in paediatric endocrinology to investigate undervirilisation or ambiguous genitalia, in adult urology to monitor biochemical response to 5-alpha reductase inhibitors, and occasionally in dermatology or endocrinology when signs of hyperandrogenism coexist with normal testosterone. Because most DHT action occurs within tissues, serum free DHT is an indirect window onto peripheral androgen metabolism rather than a direct measure of intracellular activity.
What does the Free DHT test measure?
Dihydrotestosterone is the most potent naturally occurring androgen, synthesised from testosterone by 5-alpha reductase enzymes predominantly in peripheral target tissues including skin, prostate, and hair follicles. Free DHT represents the unbound fraction not carried by sex hormone-binding globulin or albumin and is biologically active, mediating classical androgen-receptor effects in androgen-sensitive tissues. Although circulating DHT concentration is far lower than testosterone, its higher receptor affinity makes it the principal androgen in the prostate, external genitalia, and scalp hair follicles.
Measurement of free DHT is reserved for clinical scenarios in which tissue androgen action is in question despite normal testosterone. Practitioners order it to evaluate suspected 5-alpha reductase deficiency in children with ambiguous genitalia or incomplete virilisation, to monitor patients on 5-alpha reductase inhibitors for benign prostatic hyperplasia or male-pattern hair loss, and occasionally to investigate unexplained signs of hyperandrogenism when testosterone and other androgens are unremarkable. Because DHT is synthesised locally in target tissues, circulating levels correlate only loosely with intraprostatic or follicular androgen activity.
Why is the Free DHT test ordered?
- Evaluation of suspected 5-alpha reductase deficiency in infants or children with ambiguous genitalia, micropenis, or incomplete masculinisation at puberty
- Biochemical monitoring of patients on 5-alpha reductase inhibitors (finasteride, dutasteride) for benign prostatic hyperplasia or androgenetic alopecia, when treatment response is uncertain
- Investigation of unexplained signs of androgen excess — hirsutism, severe acne, androgenetic alopecia — when testosterone, DHEA-S, and androstenedione are normal or only modestly elevated
- Work-up of male infertility or sexual dysfunction when the testosterone-to-DHT ratio is suspected to be abnormal, though this is rarely the first-line investigation
- Research or specialised andrology protocols examining the testosterone-to-DHT conversion pathway in disorders of male reproductive development
- Assessment of potential androgen-receptor signalling defects, interpreted alongside androgen-receptor studies and a detailed phenotype
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
3–5 business days
Collection notes
Phlebotomy at Quest Diagnostics patient service centre; no fasting or special preparation required. Morning collection is preferred in adult males to align with the peak of testosterone secretion, though DHT itself shows less pronounced diurnal variation. Avoid collection immediately after strenuous exercise.
Specimen requirements
Minimum 1 mL serum (gel separator acceptable). Separate from cells promptly and freeze if not analysed within 48 hours; DHT is stable frozen. Note the performing laboratory for serial comparability.
What can affect Free DHT results?
These drugs directly inhibit conversion of testosterone to DHT; reduced free DHT is the intended pharmacological effect and confirms adherence and biochemical response.
Supraphysiological testosterone increases substrate for 5-alpha reductase, raising circulating DHT; interpretation requires knowledge of any exogenous androgen use.
SHBG binds DHT with lower affinity than testosterone, so free DHT is less affected by SHBG changes than free testosterone, but obesity, insulin resistance, and thyroid states can still alter the free fraction.
DHT rises during male puberty and declines modestly with ageing; paediatric reference intervals differ markedly from adult ranges and must be applied carefully.
Severe liver or kidney disease can alter sex-steroid binding proteins and steroid metabolism, complicating interpretation of any free androgen measurement.
DHT shows less pronounced diurnal variation than testosterone but modest day-to-day fluctuation; assay performance at low concentrations (in women and children) varies, and liquid chromatography–mass spectrometry is preferred over immunoassay when precision is critical.
What do Free DHT results mean?
Elevated
Elevated free DHT may reflect exogenous androgen use, upregulated 5-alpha reductase activity, or androgen-secreting tumours (rare). In women, mild elevations can accompany polycystic ovary syndrome or idiopathic hyperandrogenism, though testosterone and androstenedione are more often the dominant androgens. Artefactual elevation can occur if the assay cross-reacts with other steroids, so confirmation with liquid chromatography–mass spectrometry may be warranted.
Normal
A normal free DHT does not exclude local tissue androgen excess (intraprostatic or follicular DHT may be high when serum DHT is normal) or disorders of androgen-receptor signalling. Interpretation always requires correlation with the clinical phenotype, total and free testosterone, SHBG, and the specific reason the test was ordered.
Reduced
Low or undetectable free DHT in males suggests 5-alpha reductase deficiency (especially in infancy or at puberty), pharmacological inhibition, or severe androgen deficiency. In adults on finasteride or dutasteride, suppressed DHT confirms drug effect. In children with ambiguous genitalia, a low DHT with normal testosterone and an elevated testosterone-to-DHT ratio points strongly to 5-alpha reductase deficiency and should prompt genetic testing.
Note: Free DHT is method-dependent and not standardised across laboratories; serial monitoring should use the same assay platform. The testosterone-to-DHT ratio is often more informative than the absolute DHT level when investigating 5-alpha reductase deficiency. Because most DHT is synthesised and acts locally, circulating concentrations are an imperfect proxy for target-tissue androgen activity.
Frequently asked questions
Testosterone is the principal circulating androgen and the first-line test. DHT is synthesised from testosterone in peripheral tissues and is far more potent but circulates at much lower concentrations. Free DHT is ordered only when the clinician suspects a disorder of 5-alpha reductase or unexplained androgen effects despite normal testosterone.
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
- Wilson JD, et al. The role of 5α-reductase in androgen physiology. Endocrinology. (2001)
- Imperato-McGinley J, et al. Steroid 5α-reductase deficiency in man: an inherited form of male pseudohermaphroditism. Science. (1974)
- Traish AM, et al. The dark side of 5α-reductase inhibitors' therapy: sexual dysfunction, high Gleason grade prostate cancer and depression. Korean J Urol. (2014)
- Rosner W, et al. Position statement: Utility, limitations, and pitfalls in measuring testosterone: an Endocrine Society position statement. J Clin Endocrinol Metab. (2007)
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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