Which blood tests are relevant for hair loss?

The key points

1177, the Swedish national health guide, states that the most common cause of hair loss is heredity. Hereditary hair loss shows in no blood test.
Everyone sheds between 50 and 150 hairs a day. What gets investigated is the departure from your own baseline.
1177 names thyroid disease, iron deficiency and chronic illnesses such as diabetes among the conditions that can cause hair loss.
Internetmedicin lists CRP, haemoglobin, white cell count, a urine dipstick and thyroid tests as the sampling in a hair-loss work-up.
If you menstruate and are shedding more than usual while your periods become irregular and body hair increases, 1177 gives that as a reason to contact primary care.

What counts as hair loss

Everyone sheds between 50 and 150 hairs a day, 1177 writes. That is the hair's normal turnover, and it is not what gets investigated.

What gets investigated is a clear increase in shedding, or hair that does not come back. Internetmedicin, the Swedish clinical reference for doctors, describes telogent effluvium (telogen effluvium) as considerably more than physiological shedding, with a large amount of hair lost in the telogen phase over a short period, perhaps 1000 hairs a day. The triggers listed are infection with fever, childbirth, stress, thyroid disease, anaemia, nutritional deficiencies, chronic illnesses and certain medicines.

Several of those can be measured in blood. That is why blood tests come up at all in hair loss.

Hereditary hair loss

1177 states that the most common cause of hair loss is heredity.

Internetmedicin describes androgenetic alopecia as usually manifest in middle age in more than half of all men, and notes it can begin as early as 17 to 18 years of age. In women it affects around 10 percent, usually starting at 25 to 30. In women, 1177 says hereditary hair loss most often appears around klimakteriet (the menopause), when the hair gradually thins until the scalp shows through.

There is no blood test for this. Hereditary hair loss is judged from the pattern on the scalp, the course over time and the family history. A clean set of results therefore contradicts nothing, and an off value does not prove that the off value is what is causing the hair loss. The blood tests in a hair-loss work-up have a different job: finding the causes that can be acted on.

Iron and ferritin

1177 writes that certain illnesses can cause hair loss, naming thyroid disease, iron deficiency and chronic conditions such as diabetes. Internetmedicin counts anaemia and nutritional deficiencies among the triggers of telogen effluvium.

Ferritin is the value that reflects the body's iron stores, according to internetmedicin. That is why ferritin comes up when someone is assessed for increased shedding, particularly in people who menstruate. 1177 states that menstrual bleeding is the most common cause of iron deficiency anaemia in Sweden.

One thing about ferritin is worth knowing. The value rises with inflammation, and internetmedicin notes that a normal ferritin can still be consistent with iron deficiency. Ferritin is therefore read together with transferrin saturation and CRP.

A caveat belongs here. Internetmedicin's sampling list for hair loss covers CRP, haemoglobin, white cell count, a urine dipstick and thyroid tests, and does not name ferritin explicitly. That iron deficiency can cause hair loss comes from 1177. Which iron values are warranted in your case is decided by whoever assesses you.

The thyroid

Both an overactive and an underactive thyroid appear among the causes of hair loss.

In an underactive thyroid, 1177 describes dry skin and dry hair, and says you may also lose hair. The other symptoms listed are growing tiredness, feeling cold easily, low mood, weight gain and a slow pulse. In an overactive thyroid, hair loss is also part of the picture, alongside sweating, poor sleep, palpitations, loose stools and weight loss despite eating as usual.

Internetmedicin lists thyroid tests, meaning TSH and T4, in the sampling for a hair-loss work-up. TSH is produced in the pituitary gland and acts on the thyroid, and according to 1177 the test can show whether the gland is working as it should. High values usually mean an underactive thyroid, low values usually an overactive one.

Thyroid-driven hair loss rarely arrives alone. If hair loss is the only symptom, with no tiredness, temperature sensitivity or weight change, the thyroid is a less likely explanation, even though the test is often taken anyway to close the question.

Hormones in women

Two hormonal situations are worth keeping apart.

The first is temporary. 1177 writes that shedding a lot of extra hair in the months after childbirth is common, and that the hair usually grows back after about six months. That situation normally needs no testing at all.

The second is one 1177 names as a reason to seek care: if you menstruate and are shedding more hair than usual while your periods become irregular and you get more hair on your body. The combination of thinning hair on the scalp, increased body hair and irregular periods is what leads on to a hormonal work-up.

Internetmedicin states that assessment of testosterone level is recommended in hirsutism, meaning increased body hair, and that the most common cause of raised androgens is PMOS (previously called PCOS), polyendocrine metabolic ovarian syndrome, which explains 70 to 80 percent of all hirsutism cases. Which hormone tests apply is decided by the overall picture and by whoever assesses you. A single hormone value without that picture is hard to do anything with.

When to seek care

1177 says to contact a primary care centre if any of the following applies.

You are losing a lot of hair and feel unwell at the same time. You have lost hair and it has not come back within six months. You are losing hair from a spot where the scalp itches, is tender and may be red. You have bald patches or have lost all your hair. You have lost a lot of hair and think a medicine you take may be behind it. You menstruate and are shedding more hair than usual while your periods become irregular and you get more hair on your body.

A blood test complements that assessment. It can show whether the thyroid or your iron stores are involved, and whether any of the conditions internetmedicin lists is in the picture. It cannot see the scalp, the pattern or how long the process has been running, and it does not make a diagnosis.

Common questions

Which tests are usually taken for hair loss?

Internetmedicin lists CRP, haemoglobin, white cell count, a urine dipstick and thyroid tests in the form of TSH and T4, plus targeted sampling such as ANA, RF and anti-CCP where indicated. Iron deficiency appears as a cause of hair loss at 1177, and ferritin is the value that reflects iron stores. What gets taken in your case is decided by whoever assesses you.

Can a low ferritin alone explain my hair loss?

Iron deficiency is among the conditions 1177 lists as causing hair loss, and ferritin reflects iron stores. A single value settles nothing, though. Ferritin rises with inflammation, so a normal value can still be consistent with iron deficiency according to internetmedicin, and the most common cause of hair loss is heredity per 1177.

My TSH is normal but I am losing hair. What does that mean?

That the thyroid becomes a less likely explanation. What remains are the causes no test measures, above all hereditary hair loss and telogen effluvium after infection, childbirth or stress. 1177 sets out when to contact a primary care centre, and that list applies whatever the results look like.

How long does hair loss after childbirth last?

1177 writes that shedding a lot of extra hair in the months after childbirth is common and that the hair usually grows back after about six months. 1177 also says to contact a primary care centre if the hair has not come back within six months.

Can hereditary hair loss be seen in a blood test?

No. Hereditary hair loss is judged from the pattern on the scalp, the course over time and the family history. Blood tests are used to find or rule out the other causes, not to confirm the most common one.