It is normal to lose around 50 to 100 hairs each day. But when shedding becomes noticeably heavier, hair starts thinning, or the change continues for months, it may be worth looking for an underlying cause.
Blood tests cannot diagnose every type of hair loss. They are most useful when symptoms, medical history, or a scalp examination suggest that something happening elsewhere in the body may be affecting the hair.
What Causes Hair Loss?
Hair loss has many possible causes.[1] Pattern hair loss, also called androgenetic alopecia, is largely influenced by genetics and hormones. Alopecia areata is an autoimmune condition that can cause distinct patches of hair loss. Tight hairstyles can lead to traction alopecia, while scalp infections or inflammatory conditions can also affect hair growth.
Hair can also shed more heavily after major illness, surgery, childbirth, rapid weight loss, significant stress, or certain medications. These triggers can cause telogen effluvium, a temporary type of excessive hair shedding caused by a shift in the normal hair-growth cycle.
Nutritional and medical conditions are another part of the picture. Iron deficiency, anemia, thyroid disease, and some nutritional deficiencies can contribute to thinning or increased shedding. Because these causes may not be obvious from the scalp alone, targeted blood tests can sometimes help identify them.
What Signs Suggest You May Need Blood Work?
Not everyone with hair loss needs laboratory testing. A healthcare provider will usually consider the pattern of hair loss, symptoms, medical history, medications, diet, and recent health changes before deciding whether blood tests are appropriate.
Blood work may be considered when hair loss is persistent or unexplained, particularly if it occurs alongside:
- Ongoing tiredness or low energy
- Unexplained weight gain or weight loss
- Feeling unusually cold
- Dry skin or brittle nails
- Heavy or irregular menstrual periods
- Changes in diet, rapid weight loss, or signs of nutritional deficiency
These symptoms do not prove that a medical condition is causing the hair loss, but they can help guide further evaluation.
What Blood Tests Are Commonly Performed?
There is no single standard “hair loss panel” that is right for everyone. Testing should be based on symptoms and the type of hair loss a healthcare provider suspects.[2]
Common tests may include:
- Complete blood count (CBC): Can help identify anemia and related abnormalities.
- Iron studies, including ferritin: Can help assess iron stores and possible iron deficiency.
- Thyroid testing, such as TSH: Thyroid disorders can contribute to diffuse thinning or shedding.
- Vitamin or nutrient testing: Vitamin B12, vitamin D, zinc, or other nutrients may be checked when diet, symptoms, or medical history suggest a possible deficiency.
- Hormone testing: This may be appropriate when symptoms such as irregular periods, persistent acne, excess facial or body hair, or other signs suggest an endocrine imbalance.
Blood work is only one part of the evaluation. A provider may also examine the scalp, review medications, ask about recent illnesses or stressful events, and consider family history.
What Blood Tests Cannot Tell You
Normal blood results do not necessarily mean there is no explanation for hair loss. Many common forms are diagnosed mainly through medical history and examination rather than blood work.
Pattern hair loss, alopecia areata, traction alopecia, and some scalp conditions may have normal laboratory results. Depending on the pattern of hair loss, a dermatologist may examine the scalp more closely, use a hair-pull test [3], test for infection, or occasionally recommend a scalp biopsy.
Blood tests should therefore be viewed as one diagnostic tool rather than a complete answer on their own.
What Happens After Blood Work?
Treatment depends on what the evaluation finds. If testing identifies iron deficiency, thyroid dysfunction, or another underlying medical issue, treating that condition may help support a healthier hair-growth cycle.
If a nutritional deficiency is found, a healthcare provider may recommend dietary changes or supplementation. Supplements are not automatically helpful when levels are normal, and excessive amounts of some nutrients can cause problems.
If blood tests are normal, the next step may be to look more closely at other causes, including genetic pattern hair loss, autoimmune hair loss, traction, medication effects, or scalp conditions.
Following treatment for the specific cause is more useful than trying multiple hair-growth products without knowing what is driving the shedding.
The Bottom Line
Blood tests can be useful when hair loss may be connected to an underlying medical or nutritional issue, but they are only one part of the evaluation. The right tests depend on your symptoms, health history, and the pattern of hair loss. If shedding or thinning is persistent or unexplained, a healthcare provider can help determine whether blood work is appropriate and what other causes should be considered.
References
[1] https://www.mayoclinic.org/diseases-conditions/hair-loss/symptoms-causes/syc-20372926
[2] https://www.healthline.com/health/blood-tests-for-hair-loss