How to Prepare for a DHT (Dihydrotestosterone) Blood Test

Dihydrotestosterone is one of the most potent androgens in the body, yet a single blood value can be skewed by the time of day, a hard workout or a common hair supplement. Our editorial team explains what the DHT test shows, how to prepare for it, and which factors most often distort the result.

What a DHT test measures and why it is ordered

Dihydrotestosterone, usually shortened to DHT, is a potent androgen formed when the enzyme 5-alpha reductase converts testosterone inside tissues such as the skin, hair follicles and prostate. Only a small share of circulating androgen exists as DHT, yet it binds the androgen receptor several times more tightly than testosterone itself.

Physicians order a serum DHT test for a fairly narrow set of reasons. These include evaluating ambiguous genitalia or suspected 5-alpha reductase deficiency in children, investigating hirsutism and androgen excess in women, and checking how strongly a drug such as finasteride or dutasteride is suppressing the enzyme in men treated for hair loss or an enlarged prostate.

In sports medicine the test occasionally appears in broader hormone panels, for example when a clinician is assessing acne, scalp hair thinning or prostate symptoms in someone who uses or has used androgens. On its own, however, DHT is rarely the deciding number. It is interpreted together with total and free testosterone, SHBG, LH and estradiol.

Because DHT circulates in low concentrations, usually reported in nanograms per deciliter or picograms per milliliter in US laboratories, small technical errors matter. That is the main reason preparation deserves attention: a poorly timed draw or an overlooked medication can shift the result enough to change how a doctor reads it.

Timing: morning draws and the daily hormone rhythm

Androgens follow a circadian rhythm. In younger men testosterone peaks in the early morning and drifts down through the afternoon, and DHT broadly follows its precursor. A large analysis of community-dwelling men by Brambilla and colleagues found that afternoon values can be meaningfully lower than morning values, especially before middle age.

For that reason most US labs and endocrinology guidelines recommend drawing androgen tests between roughly 7 and 10 a.m. If you work night shifts, tell the ordering clinician, because your rhythm may be shifted and the ideal collection time may differ from the standard advice.

Consistency is just as important as the exact hour. If you are tracking DHT over months, for instance to see how a prescribed 5-alpha reductase inhibitor is working, try to book every draw at a similar time of day, at the same laboratory, and under similar conditions of sleep and activity.

Women who menstruate may be asked to test during a particular phase of the cycle, typically the early follicular phase, so that results can be compared with reference ranges built on that window. Your gynecologist or endocrinologist will specify the day if it is relevant.

Food, alcohol, exercise and sleep before the test

A DHT test does not always require strict fasting, but many clinicians order it alongside glucose, lipids or other hormones, so labs often ask for an overnight fast of 8 to 12 hours. Research by Caronia and colleagues showed that a glucose load can acutely lower testosterone, which is another reason a fasting morning sample is the cleaner choice.

Plain water is allowed and actually helpful, because good hydration makes the venipuncture easier. Coffee with sugar, juice and breakfast should wait until after the draw. If you take medications that must be taken with food, ask the clinician how to time them rather than skipping them on your own.

Alcohol in the preceding day or two can temporarily disturb androgen metabolism and the liver handling of hormones. Hard training, an endurance race or an all-night shift can also lower androgen values for a short period. A calm 24 to 48 hours before testing gives a result that reflects your usual state.

A practical checklist that most US labs would accept looks like this:

• Schedule the draw for early morning, ideally before 10 a.m.
• Fast overnight if other fasting tests are on the same order; water is fine.
• Avoid alcohol for at least 24 hours and skip intense workouts the day before.
• Get a normal night of sleep and arrive a few minutes early to sit quietly.
• Bring a written list of every medication, supplement and topical product you use.

Medications and supplements that can change the result

The single most important factor is drug therapy. Finasteride and dutasteride are designed to block 5-alpha reductase, and dutasteride in particular can suppress serum DHT by more than 90 percent, as Clark and colleagues documented in men with benign prostatic hyperplasia. A low DHT in someone taking these drugs is expected, not a disease.

Testosterone therapy, topical testosterone gels and any non-prescribed androgen use tend to raise DHT, sometimes markedly. Topical products applied to the skin are a particular source of high DHT, because skin is rich in 5-alpha reductase. Your clinician needs to know about all of them, including products you stopped recently.

High-dose biotin is a separate issue. The FDA has warned that biotin, common in hair, skin and nail supplements, can interfere with immunoassays that use biotin-streptavidin chemistry. Many labs measure DHT by liquid chromatography with tandem mass spectrometry, which is less affected, but pausing biotin for at least 72 hours, if your doctor agrees, removes the doubt.

Never discontinue a prescribed drug simply to get a "cleaner" number. In most cases the point of the test is to see your hormones under your real treatment conditions, and stopping a medication can be risky in its own right.

Reading the result and when to retest

Reference ranges for DHT vary widely between laboratories, methods and sexes, so the range printed on your report is the one that applies. Mass spectrometry and immunoassay values are not directly interchangeable, which is why repeat tests are best done with the same method.

A DHT result outside the range is a starting point for interpretation rather than a diagnosis. Clinicians look at the ratio of testosterone to DHT, at SHBG and at the clinical picture. A high ratio may point toward 5-alpha reductase deficiency, whereas elevated DHT with acne and hair loss may simply reflect high androgen exposure.

The Endocrine Society notes that hormone assays carry analytical variability, and a single abnormal value, especially a borderline one, is usually confirmed with a repeat draw. If your first sample was taken in the afternoon, after a hard training block or during illness, a retest under standard conditions is reasonable.

Elevated DHT has been studied in relation to prostate growth, hair loss and acne, but the long-term significance of moderately raised levels in healthy men is still debated, as reviewed by Swerdloff and colleagues. Avoid drawing conclusions from internet calculators; discuss the full panel with a physician.

Conclusions of the editorial team

A DHT test is easy to perform but easy to distort. Morning timing, a quiet day beforehand, avoidance of alcohol and heavy training, and an honest medication list are the habits that make the number meaningful.

The biggest influences on the result are drugs that act on androgen metabolism, especially 5-alpha reductase inhibitors and any form of testosterone. Report them clearly instead of stopping them on your own initiative.

Interpretation belongs in the context of a full androgen panel and a clinical examination. Borderline findings are typically repeated before any decision is made.

If you found this guide useful, our editorial team also suggests reading about how to prepare for a total and free testosterone test, what SHBG tells you about hormone balance, and how hematocrit is monitored in people receiving androgen therapy.

References

1. Swerdloff RS, Dudley RE, Page ST, Wang C, Salameh WA. Dihydrotestosterone: biochemistry, physiology, and clinical implications of elevated blood levels. Endocr Rev. 2017;38(3):220–254.
2. Brambilla DJ, Matsumoto AM, Araujo AB, McKinlay JB. The effect of diurnal variation on clinical measurement of serum testosterone and other sex hormone levels in men. J Clin Endocrinol Metab. 2009;94(3):907–913.
3. Rosner W, Auchus RJ, Azziz R, Sluss PM, Raff H. Position statement: utility, limitations, and pitfalls in measuring testosterone: an Endocrine Society position statement. J Clin Endocrinol Metab. 2007;92(2):405–413.
4. Clark RV, Hermann DJ, Cunningham GR, Wilson TH, Morrill BB, Hobbs S. Marked suppression of dihydrotestosterone in men with benign prostatic hyperplasia by dutasteride, a dual 5alpha-reductase inhibitor. J Clin Endocrinol Metab. 2004;89(5):2179–2184.
5. Caronia LM, Dwyer AA, Hayden D, Amati F, Pitteloud N, Hayes FJ. Abrupt decrease in serum testosterone levels after an oral glucose load in men: implications for screening for hypogonadism. Clin Endocrinol (Oxf). 2013;78(2):291–296.
6. 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.
7. US Food and Drug Administration. The FDA warns that biotin may interfere with lab tests: FDA safety communication. Silver Spring (MD): FDA; 2017.
8. https://masscraftusa.com/cabergolin-05-mg-balkan-pharmaceuticals-33647-us