Hormones
Dihydrotestosteron
A strong form of testosterone that acts mainly in the skin; a blood value says little about hereditary hair loss.
Everything about this testWhat it measures
Dihydrotestosterone (DHT) is made in the body from testosterone by the enzyme 5-alpha reductase. This conversion happens mainly in the tissues themselves, such as the skin, the hair follicles and the prostate, and that is also where DHT does its work. DHT is stronger than testosterone and is important for the development of the male sex organs and for body and beard hair. This analysis measures the amount of DHT in blood; that is only part of what happens in the tissues.
- Too much male hormone in women with excess hair growth, acne or thinning hair, in addition to testosterone
- The effect of medicines that block the conversion of testosterone into DHT, such as finasteride and dutasteride
- Use of testosterone, anabolic steroids or DHT-like substances
High
In men, a raised DHT is mainly due to the use of testosterone, anabolic steroids or DHT-like substances. In women, a raised value can fit too much male hormone, for example with PCOS, with symptoms such as excess hair growth, acne, irregular periods and thinning hair on the crown. Hereditary baldness is not explained by a high blood value: in that case the hair follicles are oversensitive to male hormones, while the amount of hormone in the blood is often simply normal. So a high value does not mean you will go bald, and a normal value does not mean you will not.
Low
A low DHT fits the use of finasteride or dutasteride, drugs for baldness or an enlarged prostate that block the conversion of testosterone into DHT. In men, a low value can also go together with a low testosterone; the testosterone itself then says more. In women, a low value has no clear meaning. A congenital deficiency of the enzyme 5-alpha reductase is rare and is noticed early in life.
If your result is abnormal
With an abnormal value, the GP first looks at medicines and substances such as finasteride, testosterone or anabolic steroids, and assesses testosterone and SHBG. In women with a raised value and an irregular cycle or excess hair growth, tests for PCOS or a referral to a gynecologist or internist-endocrinologist usually follow. With hair loss without other symptoms, a DHT result usually does not change the approach.
Reliability
DHT in blood says little about hair loss, because DHT acts mainly in the skin and the hair follicles themselves. According to the practice information of the Dutch dermatologists' society (NVDV), hereditary hair loss is diagnosed from the pattern of hair loss and the medical history; blood tests are only needed in a targeted way, for example for iron and thyroid, or for male hormones in women with other signs of too much male hormone. DHT is mainly useful for a specific question, and then together with testosterone. The measurement is technically difficult and results differ by laboratory and measurement method.
Limitations
- Medicines and substances: finasteride and dutasteride lower DHT; testosterone and anabolic steroids raise it.
- The value in blood gives only a limited picture of the amount and action of DHT in the skin and the hair follicles.
- Reference values differ by laboratory, measurement method, sex and age; generally used cut-off values are lacking.
- In women, hormonal contraception makes the assessment of male hormones unreliable.
How common is this
Hereditary hair loss is very common: among people aged 70, about 8 in 10 men and 3 in 10 women are affected. About 5 in 100 women have excess hair growth; usually the amount of male hormone is then normal and the skin is more sensitive to it. How often an abnormal DHT is the cause of symptoms has not been recorded in Dutch figures.
Who is this useful for
Useful in limited situations: in women with excess hair growth, acne or hair loss together with other signs of too much male hormone, in addition to testosterone and SHBG, and for a specific question from a specialist. Not useful to diagnose or predict hereditary baldness, nor to decide whether a hair loss treatment will work: the diagnosis is made from the pattern of hair loss. For men without symptoms the test has no value.
Downsides and risks
- A DHT result can wrongly be seen as the explanation for hair loss and lead to treatments that do not help, or to the use of finasteride without properly weighing up the side effects.
- A slightly abnormal value without symptoms can cause unnecessary worry and unnecessary follow-up tests.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results