Hair loss: which blood tests to ask for, and what the results actually mean

Which blood tests should you ask for if your hair is falling out?

If your hair is thinning all over or you are shedding more than usual, the tests with the strongest case behind them are few. Ask for serum ferritin, which shows your iron stores, a full blood count (CBC) to look for anaemia, and TSH to check your thyroid. Many doctors add vitamin D, which is reasonable in a region where low levels are common. For women with irregular periods, acne or new facial hair, hormone tests such as total testosterone come next.

That short list catches the treatable causes that blood can reveal. It will not explain every case, because the two most common types of hair loss, pattern hair loss and shedding after a stressful event, usually come with completely normal blood results. A normal result is still useful information. It tells you and your doctor that the cause lies elsewhere, and it saves you money on supplements you do not need.

What you should be wary of is the long "hair analysis" package that many private labs and salons now sell, with twenty or more items including copper, selenium, biotin and a full hormone panel for men. Most of these add cost without changing what happens next. The sections below go through each test, what it looks for and when it earns its place.

Ferritin: the test that matters most, especially for women

Ferritin is the protein your body stores iron in, and a low ferritin is one of the most frequent findings when women with hair shedding have their blood checked. It falls before haemoglobin does, so your CBC can look normal while your iron stores are already running low. Heavy periods, pregnancy, breastfeeding, a diet light on red meat, and repeated blood donation all drain it.

A study from the dermatology department at Cairo University, published in 2013, compared 80 women aged 18 to 45 with hair loss against 40 women without it. Average ferritin was 14.7 µg/L in women with telogen effluvium and 23.9 µg/L in women with female pattern hair loss, against 43.5 µg/L in the women with healthy hair. The researchers found that ferritin below roughly 27 to 30 µg/L best separated the women with hair loss from those without.

This matters because many lab reports flag ferritin as normal from about 10 or 15 µg/L upwards, so a result of 18 may be printed without any warning mark. That number is enough to make blood, but may not be enough for a healthy hair cycle. If your ferritin is in this grey zone, it is worth discussing with your doctor rather than accepting the word "normal" on the page. Iron tablets cause side effects and can be harmful in people who do not need them, so let a doctor decide whether and how you should take them.

Ferritin also rises with infection and inflammation, so a high or normal figure taken during an illness can hide low stores. If you had a fever recently, a repeat test a few weeks later gives a truer picture.

Thyroid tests and the CBC: cheap, quick and worth doing

Both an underactive and an overactive thyroid can cause diffuse thinning, because thyroid hormone helps set the pace of the hair growth cycle. TSH is the screening test. If it is abnormal, your doctor will usually add free T4 and sometimes thyroid antibodies to find the cause. Hair often improves once the thyroid is treated, though it can take several months to show.

The full blood count looks at your red cells, white cells and platelets. It picks up anaemia, which can come from low iron, low vitamin B12 or folate, or other causes that need their own investigation. In parts of the region where thalassaemia trait is common, a CBC can also show small red cells that are not due to iron at all, which is one more reason to test ferritin rather than assume.

One practical warning applies here. Many hair, skin and nail supplements contain high doses of biotin, and biotin can interfere with the way many labs measure thyroid hormones. A detailed 2018 review in Endocrine Reviews describes how it can make results look like an overactive thyroid when the gland is perfectly normal. If you take any such supplement, tell the lab and your doctor before the test and ask whether you should pause it beforehand.

Shedding two or three months after a fever, birth or diet: telogen effluvium

Each hair on your head goes through a growing phase lasting years, then a resting phase of a few months, after which it falls out. A shock to the body, such as a high fever, a severe infection, surgery, childbirth, a crash diet or a period of intense stress, can push many hairs into the resting phase at the same time. The shedding comes later, which is why people rarely connect it to the cause.

That delay is the single most useful fact about this condition. Shedding typically begins about two to three months after the trigger, so a woman who gave birth in spring may notice hair in the shower drain in early summer. Hairs come out from all over the scalp, often with a small white bulb at the root. You do not go bald from it. The NHS notes that losing 50 to 100 hairs a day is normal, and in telogen effluvium the number can be several times higher for a while.

Researchers at Umm Al-Qura University in Makkah reviewed 343 patients seen in dermatology clinics for hair loss after COVID-19 between 2020 and 2022. Telogen effluvium made up 86.7 percent of the cases they could classify, nearly half of patients noticed more than 120 hairs a day, and half saw hair gathering on the pillow. The same pattern follows typhoid, dengue, malaria and any illness with a high fever.

Most telogen effluvium settles within about six months without treatment, and the regrowth then takes several more months to show because hair grows only about a centimetre a month. Blood tests still help, because low ferritin or a thyroid problem can keep the shedding going. If it carries on beyond six months, see a doctor to look for a second cause.

Pattern hair loss in men and women: when blood tests help and when they do not

Male pattern hair loss, or androgenetic alopecia, is the most common type of all. It starts with a receding hairline at the temples or thinning at the crown, runs in families, and is driven by the normal male hormone dihydrotestosterone acting on hair follicles that are genetically sensitive to it. Your hormone levels are usually normal. For a man with this classic pattern and no other symptoms, blood tests rarely add anything, and a full hormone panel sold as part of a hair package is money spent for little return.

Female pattern hair loss looks different. The front hairline usually stays in place, while the parting widens and the crown thins, so the scalp shows more under bright light. Many women with it also have normal hormones. Ferritin, CBC and TSH are still worth checking, because low iron often sits alongside pattern loss and makes it worse, as the Cairo study showed.

Hormone testing becomes worthwhile when there are other signs of excess androgens: irregular or absent periods, persistent acne, or coarse hair growing on the chin, upper lip or chest. These point towards polycystic ovary syndrome (PCOS), which is common in women across the Arab world. In that situation your doctor may order total testosterone, sometimes with SHBG to estimate the free fraction, DHEAS from the adrenal glands, prolactin, and occasionally 17-hydroxyprogesterone to look for a hereditary adrenal condition. Blood for these is usually taken in the first days of the cycle and in the morning.

Vitamin D, zinc and biotin: what the evidence actually shows

Vitamin D is linked to hair loss in several studies. In the Cairo study, women with hair loss had much lower vitamin D than women without it. But a link is not proof that vitamin D causes the loss, and there is little good evidence that taking vitamin D regrows hair in people who are not deficient. Testing is reasonable because deficiency is very common across the Gulf and the Levant and is worth treating for bone health anyway. Just do not expect a vitamin D course to be the answer to your hair on its own.

Zinc deficiency can cause hair loss, but it is uncommon in people who eat a varied diet. A study at Benha University in Egypt measured zinc and biotin in 60 men with pattern hair loss and 60 healthy men. Zinc was lower in the men with hair loss, yet neither zinc nor biotin levels tracked how severe the hair loss was. Testing zinc makes sense if you have had weight loss surgery, chronic diarrhoea or bowel disease, or a very restricted diet. Taking zinc for months without a deficiency can lower your copper and cause anaemia.

Biotin is the supplement most often sold for hair, and the evidence is the thinnest. A 2017 review found only 18 reported cases where biotin helped hair or nails, and every one of those people had an underlying condition that caused deficiency. There is no good evidence that it helps healthy people. A 2019 review of vitamins and minerals in hair loss, led by dermatologists in Riyadh and Miami, reached the same overall conclusion: supplements help when you are deficient, and the evidence beyond that is not convincing.

So be sceptical when a clinic recommends a large vitamin panel followed by an expensive multivitamin for hair. Testing what is likely to be low, and correcting what is genuinely low, is the approach the research supports.

Other causes your doctor may look for

Several common causes of hair loss are diagnosed by looking at the scalp, not by blood tests. Alopecia areata causes smooth, round bald patches that appear suddenly, sometimes in the beard or eyebrows. It is an autoimmune condition, and while there is no blood test that confirms it, your doctor may check your thyroid because the two often occur together. Traction alopecia comes from hair being pulled tightly for years, for example under a tight bun, braids or a firmly fixed headscarf, and shows as thinning along the hairline and temples.

Fungal infection of the scalp, called tinea capitis, is common in children in the region. It causes scaly patches with broken hairs and sometimes a swollen, tender lump. It needs a doctor and prescription antifungal treatment by mouth, because creams alone do not reach the root. Medicines can also cause shedding, including some epilepsy drugs, isotretinoin for acne, blood thinners and chemotherapy. If you suspect a medicine, talk to the doctor who prescribed it and do not stop it on your own.

Rarely, specific infections such as secondary syphilis cause patchy, "moth-eaten" hair loss, and a doctor who suspects it will order a targeted blood test. That is a good example of why tests should follow the examination, rather than a long list being ordered first in the hope that something turns up.

Warning signs: when hair loss needs a doctor soon

Most hair loss is not dangerous, even though it is upsetting. A few patterns, however, need to be seen by a doctor or dermatologist rather than handled with a lab package or a pharmacy shampoo. Scarring hair loss is the most important. In it, the follicles are destroyed by inflammation, and the hair cannot grow back once that happens, so early treatment protects what remains.

In women, hair loss that comes with a rapidly deepening voice, fast-growing body hair or a change in body shape over a few months needs prompt assessment, because a sudden rise in male hormones is different from the slow picture of PCOS. In children, any patchy hair loss with scaling should be checked, since scalp ringworm spreads to brothers, sisters and classmates.

Bring photographs taken a few weeks apart, a list of any illness, pregnancy, surgery or diet in the past six months, and every medicine and supplement you take. That information does more to identify the cause than a long panel of tests.

How to prepare for your hair loss blood tests

A few simple steps make the results more reliable. Most of these tests do not need fasting, but if your doctor adds glucose or lipids to the same sample, you may be asked to fast overnight. Morning samples are best for hormone tests, and women having testosterone checked are often asked to test in the first week of the cycle.

Ask for the results with the lab's reference range printed beside each number, and keep the paper or a photo. Ranges vary between labs and machines, and comparing a ferritin of 20 this year with 45 after treatment is only meaningful if you know both came from comparable methods. If your local lab has no quality accreditation and a result looks out of keeping with how you feel, repeating it at a larger lab is reasonable.

Finally, give any treatment time before judging it. Hair grows slowly, so even when the cause is found and corrected, it is usually three to six months before shedding falls and longer before your hair looks fuller.

Sources

• Rasheed H, Mahgoub D, Hegazy R et al: Serum ferritin and vitamin d in female hair loss: do they play a role?, Skin pharmacology and physiology, 2013
• Abdulwahab RA, Aldajani BM, Natto NK et al: Prevalence of Hair Loss After COVID-19 Infection in Makkah Region, Saudi Arabia, Cureus, 2022
• El-Esawy FM, Hussein MS, Ibrahim Mansour A et al: Serum biotin and zinc in male androgenetic alopecia, Journal of cosmetic dermatology, 2019
• Almohanna HM, Ahmed AA, Tsatalis JP et al: The Role of Vitamins and Minerals in Hair Loss: A Review, Dermatology and therapy, 2019
• Patel DP, Swink SM, Castelo-Soccio L et al: A Review of the Use of Biotin for Hair Loss, Skin appendage disorders, 2017
• Favresse J, Burlacu MC, Maiter D et al: Interferences With Thyroid Function Immunoassays: Clinical Implications and Detection Algorithm, Endocrine reviews, 2018
• NHS: Hair loss