Blood Tests for Hair Loss

Blood tests for hair loss are a key part of evaluating unexplained hair shedding, especially when telogen effluvium is suspected. These tests help clinicians identify underlying medical issues that may contribute to hair loss, such as iron deficiency, thyroid dysfunction, or vitamin and mineral imbalances. Understanding which blood tests are most relevant and how to interpret them can empower individuals experiencing hair shedding to have informed conversations with their healthcare providers.

Why blood tests matter for hair shedding (and when they don’t)

Blood tests play an important role in the assessment of hair shedding, particularly when the cause is not immediately obvious. They can uncover treatable medical conditions such as iron deficiency, thyroid disorders, or vitamin deficiencies that may contribute to diffuse hair loss. Identifying these issues early can guide targeted treatment and improve outcomes for those experiencing excessive shedding.

However, blood tests are not always necessary for every case of hair loss. In classic telogen effluvium, where there is a clear trigger and a typical pattern of shedding, laboratory work may not always reveal an abnormality. Sometimes, all results return within normal ranges, yet shedding persists due to the natural hair cycle response to stress or illness. It is important to understand both the value and the limitations of blood work in the context of hair loss.

Unlike scarring forms of hair loss, telogen effluvium does not destroy hair follicles, and regrowth is usually possible once the underlying cause is addressed. The diagnosis is often based on history and examination, but blood tests can help rule out other contributing factors.

What blood work can and can’t prove

Blood tests can identify deficiencies or imbalances that may contribute to hair shedding, such as low ferritin, abnormal thyroid function, or vitamin deficiencies. They can also help rule out more serious underlying health conditions. However, normal blood work does not exclude telogen effluvium, as the condition can occur even when all laboratory values are within reference ranges.

It is important to note that blood tests cannot directly diagnose telogen effluvium. Instead, they provide supportive information and help exclude other causes. The diagnosis relies on a combination of clinical history, examination findings, and exclusion of other conditions.

What to tell your clinician before ordering labs

Providing your clinician with a thorough history before blood tests are ordered can improve the accuracy and relevance of the results. Details about your hair shedding pattern, recent life events, and any medications or supplements you are taking are all important. This information helps your healthcare provider select the most appropriate tests and interpret the results in the right context.

Being open about potential triggers and your overall health can also prevent unnecessary testing and ensure that any abnormal results are not due to temporary or unrelated factors. Accurate information leads to better, more personalized care.

Shedding pattern and timing

Describe when your hair shedding started, how quickly it progressed, and whether it is ongoing or improving. Note if the shedding is diffuse (all over the scalp) or patchy. Timing is crucial, as telogen effluvium often begins two to three months after a trigger.

Sharing this timeline helps your clinician correlate potential causes with the onset of shedding and decide which labs are most relevant for your situation.

Recent triggers (illness, stress, weight loss, postpartum)

Inform your clinician about any recent illnesses, surgeries, major stressors, rapid weight changes, or if you have recently given birth. These events are common triggers for telogen effluvium and can influence which blood tests are necessary.

Understanding these triggers allows your healthcare provider to focus on the most likely causes and avoid unnecessary or redundant testing.

Medications and supplements that can affect results

List all prescription medications, over-the-counter drugs, and supplements you are taking. Some substances, such as biotin, can interfere with certain blood tests, especially thyroid function tests. Others, like iron or vitamin D supplements, may affect lab results and interpretation.

Providing a complete list ensures your clinician can interpret your lab results accurately and may advise you to pause certain supplements before testing.

Core blood tests for hair loss blood work

Several blood tests are commonly ordered when evaluating unexplained hair shedding. These tests help identify deficiencies or imbalances that may contribute to hair loss and guide further management. The most frequently used tests include a complete blood count (CBC), ferritin and iron studies, thyroid panel, vitamin D, vitamin B12, and zinc.

Each of these tests serves a specific purpose and can provide valuable insights into your overall health and potential causes of hair shedding. Understanding what each test measures and why it is important can help you prepare for your appointment and interpret your results.

CBC (complete blood count)

A complete blood count (CBC) evaluates the levels of different blood cells, including red blood cells, white blood cells, and platelets. It is used to detect anemia, infection, and other blood disorders that may contribute to hair loss. Anemia, particularly iron deficiency anemia, is a well-known cause of diffuse hair shedding.

While a normal CBC does not rule out all causes of hair loss, it is a useful starting point for identifying underlying health issues that may require further investigation.

Ferritin and iron studies

Ferritin is a protein that stores iron in the body and is considered the most sensitive indicator of iron stores. Low ferritin levels can be associated with increased hair shedding, even if hemoglobin and other iron parameters are normal. Iron studies may also include serum iron, total iron-binding capacity (TIBC), and transferrin saturation.

Assessing ferritin and iron status is especially important for menstruating women, vegetarians, and individuals with a history of blood loss or poor dietary intake.

Thyroid panel

Thyroid function tests, typically starting with thyroid-stimulating hormone (TSH), assess how well the thyroid gland is working. Both hypothyroidism and hyperthyroidism can cause diffuse hair shedding. If TSH is abnormal, additional tests such as free T4 or thyroid antibodies may be ordered.

Thyroid dysfunction is a common and treatable cause of hair loss.

Vitamin D

Vitamin D plays a role in hair follicle health and immune regulation. Deficiency has been linked to various types of hair loss, including telogen effluvium. Testing vitamin D levels can help identify a deficiency that may be contributing to shedding.

Supplementation should only be started if a deficiency is confirmed.

Vitamin B12

Vitamin B12 is essential for healthy red blood cell production and nervous system function. Deficiency can lead to anemia and may contribute to hair shedding. Testing B12 levels is particularly important for individuals with dietary restrictions or absorption issues.

As with other nutrients, supplementation should be guided by confirmed deficiency.

Zinc

Zinc is a trace mineral involved in hair follicle function and immune health. Low zinc levels have been associated with increased hair shedding, though true deficiency is uncommon in developed countries. Testing may be considered if dietary intake is low or other symptoms are present.

Zinc supplementation should only be considered if a deficiency is confirmed.

Ferritin and iron: how to interpret results for shedding

Interpreting ferritin and iron studies can be complex, as different components reflect various aspects of iron metabolism. Ferritin is the most reliable marker of iron stores, while serum iron and transferrin saturation provide additional information. Understanding the relationship between these values is essential for accurate diagnosis and management.

Low ferritin can be associated with increased hair shedding, even when other iron parameters, such as hemoglobin, are normal. This highlights the importance of checking ferritin specifically when evaluating unexplained hair loss.

Ferritin vs. iron vs. hemoglobin

Ferritin reflects the body’s stored iron, while serum iron measures circulating iron in the blood. Hemoglobin is a protein in red blood cells that carries oxygen. It is possible to have low ferritin (depleted iron stores) with normal hemoglobin and serum iron, especially in early or mild deficiency.

For hair loss evaluation, ferritin is often the most sensitive indicator. A normal hemoglobin does not rule out low ferritin as a contributor to hair shedding.

Low ferritin with normal CBC

Some individuals experience significant hair shedding despite a normal complete blood count. In these cases, low ferritin may be the only abnormal finding. This scenario is common in women with heavy menstrual bleeding or those with limited dietary iron intake.

Addressing low ferritin can help reduce shedding, but iron supplementation should only be started after confirming deficiency and under medical supervision.

When iron studies are needed

Iron studies, including serum iron, TIBC, and transferrin saturation, may be ordered if ferritin is borderline or if there is suspicion of more complex iron metabolism issues. These tests provide a more comprehensive picture of iron status and can help distinguish between different types of anemia.

Your clinician will determine if additional iron studies are necessary based on your symptoms, history, and initial test results.

Thyroid testing: TSH and beyond

Thyroid function is closely linked to hair health. Both underactive and overactive thyroid disorders can cause diffuse hair shedding. Blood tests for thyroid function typically begin with TSH, but additional tests may be needed based on initial results and clinical suspicion.

Identifying and treating thyroid dysfunction can lead to improvement in hair shedding, but it is important to interpret results in the context of symptoms and other findings.

Typical starting test (TSH)

TSH (thyroid-stimulating hormone) is the standard initial test for evaluating thyroid function. Abnormal TSH levels can indicate hypothyroidism or hyperthyroidism, both of which can contribute to hair loss.

If TSH is within the reference range and there are no other symptoms, further thyroid testing may not be necessary.

When free T4 or thyroid antibodies may be added

If TSH is abnormal, or if there are symptoms suggestive of thyroid disease, additional tests such as free T4 and thyroid antibodies may be ordered. Free T4 provides information about the active thyroid hormone level, while thyroid antibodies can help diagnose autoimmune thyroid conditions.

These additional tests are not always needed but can provide valuable information in complex cases or when autoimmune thyroid disease is suspected.

Vitamin and mineral labs (vitamin D, B12, zinc)

Testing for vitamin D, B12, and zinc is sometimes included in the evaluation of hair loss, especially when there are risk factors for deficiency. These nutrients play important roles in hair follicle health, immune function, and overall well-being.

However, routine testing of these vitamins and minerals is not always necessary for every individual with hair shedding. Testing should be guided by clinical suspicion and risk factors.

When testing makes sense

Testing vitamin D, B12, and zinc is most appropriate when there are symptoms or risk factors for deficiency, such as dietary restrictions, malabsorption, or chronic illness. For example, individuals who avoid animal products may be at risk for B12 deficiency, while those with limited sun exposure may have low vitamin D.

Discuss your personal risk factors with your clinician to determine which tests are most relevant for you.

Avoiding unnecessary testing and over-supplementation

Unnecessary testing can lead to confusion and may result in inappropriate supplementation. Taking high doses of vitamins or minerals without confirmed deficiency can be harmful and may mask other health issues.

It is important to only start supplements if a deficiency is confirmed through blood testing and to follow your clinician’s guidance regarding dosage and duration.

Other tests sometimes used (based on symptoms)

In some cases, additional blood tests may be ordered based on specific symptoms or findings during the evaluation. These tests are not routinely performed for all cases of hair shedding but may be necessary to rule out other medical conditions.

Your clinician will determine if further testing is needed based on your individual history, symptoms, and examination findings.

Metabolic panel and liver/kidney function

A metabolic panel assesses electrolyte balance, blood sugar, and organ function, including the liver and kidneys. Abnormalities in these systems can sometimes contribute to hair loss or indicate underlying health issues that require attention.

These tests are usually reserved for cases where there are additional symptoms or risk factors for systemic illness.

Inflammation/autoimmune screening when indicated

If there are signs of inflammation or autoimmune disease, such as joint pain, rashes, or other systemic symptoms, tests like erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), or autoimmune panels may be ordered.

These tests help identify underlying conditions that can cause hair shedding, such as lupus or other connective tissue diseases.

Hormone testing (when signs of androgen excess are present)

Hormone testing may be considered if there are signs of androgen excess, such as acne, irregular periods, or increased facial/body hair. Tests may include total and free testosterone, DHEAS, or other relevant hormones.

These tests are not routinely performed for diffuse shedding but may be indicated when symptoms suggest an underlying hormonal imbalance.

Preparing for labs and avoiding common mistakes

Proper preparation for blood tests can improve the accuracy of results and reduce the likelihood of needing repeat testing. Following your clinician’s instructions regarding fasting, timing, and medication or supplement use is essential.

Being aware of common pitfalls, such as biotin interference or testing too soon after a triggering event, can help ensure that your results are reliable and actionable.

Fasting and time of day

Some blood tests, such as iron studies, may require fasting or be influenced by the time of day. Your clinician will provide specific instructions if fasting is necessary. Following these guidelines helps ensure accurate and consistent results.

If you are unsure about preparation requirements, ask your healthcare provider or the laboratory for clarification before your appointment.

Biotin and lab interference

Biotin supplements, often found in hair and nail products, can interfere with certain blood tests, particularly thyroid function tests. High biotin intake may lead to falsely high or low results, potentially causing misdiagnosis.

If you are taking biotin, inform your clinician. You may be advised to stop biotin supplements for several days before testing to avoid inaccurate results.

Repeating tests and follow-up timing

In some cases, blood tests may need to be repeated to confirm results or monitor progress after starting treatment. The timing of repeat testing depends on the specific test and the underlying condition being managed.

Follow your clinician’s recommendations regarding when to recheck labs, as premature testing may not reflect true changes in your health status.

Interpreting results in the context of telogen effluvium

Interpreting blood test results for hair shedding requires considering the broader clinical picture. Normal laboratory values do not exclude telogen effluvium, as the condition can occur even when all tests are within reference ranges.

A careful review of recent triggers, timing of shedding, and examination findings is essential for accurate diagnosis and management.

Normal labs do not rule out telogen effluvium

It is possible to have normal blood tests and still experience telogen effluvium. The condition is often a response to a physical or emotional stressor, and laboratory work may not reveal any abnormalities.

Diagnosis is based on the pattern of shedding, history of triggers, and exclusion of other causes rather than lab results alone.

Linking a trigger + timing + exam findings

A strong link between a known trigger (such as illness, surgery, or childbirth), the timing of hair shedding, and examination findings (such as a positive hair pull test) supports the diagnosis of telogen effluvium.

Blood tests provide supportive information but must be interpreted alongside clinical findings for the most accurate diagnosis.

When to see a doctor

While many cases of hair shedding resolve on their own, certain signs and symptoms warrant prompt medical evaluation. Early intervention can help identify serious underlying conditions and prevent permanent hair loss.

If you experience any of the following red flags, persistent or severe shedding, or special circumstances such as pregnancy or postpartum changes, seek medical advice.

Red flags (scarring, patchy loss, rapid progression)

Seek urgent care if you notice patchy hair loss, scalp pain, redness, swelling, or signs of infection. These symptoms may indicate scarring alopecia or other serious conditions that require immediate attention.

Rapid progression of hair loss or associated systemic symptoms should also prompt a visit to a healthcare provider.

When shedding is persistent or severe

If hair shedding continues for more than six months, is severe, or is associated with other unexplained symptoms, further evaluation is recommended. Persistent shedding may indicate an ongoing trigger or an underlying medical condition that needs to be addressed.

Early assessment can help identify treatable causes and improve the chances of hair regrowth.

Pregnancy, postpartum, and other special situations

Hair shedding is common after pregnancy (postpartum telogen effluvium) and usually resolves on its own. However, if shedding is excessive, prolonged, or accompanied by other symptoms, consult a healthcare provider. For more, see Postpartum telogen effluvium.

Special consideration is also needed for individuals with chronic illness, recent surgery, or other unique circumstances. Discuss your specific situation with your clinician for personalized guidance.

FAQ

What are the most important blood tests for hair loss?

The most important blood tests for hair loss typically include a complete blood count (CBC), ferritin and iron studies, thyroid panel (TSH), and sometimes vitamin D, B12, and zinc. These tests help identify common deficiencies or imbalances that may contribute to hair shedding.

Can low ferritin cause telogen effluvium even if my hemoglobin is normal?

Yes, low ferritin can be associated with telogen effluvium even when hemoglobin and other blood counts are normal. Ferritin reflects iron stores, and low levels may contribute to hair shedding before anemia develops.

Which thyroid tests are best for hair shedding?

Thyroid-stimulating hormone (TSH) is the standard initial test for evaluating thyroid function in cases of hair shedding. If TSH is abnormal or if there are symptoms of thyroid disease, additional tests such as free T4 and thyroid antibodies may be added.

Should everyone with shedding test vitamin D, B12, and zinc?

Not everyone with hair shedding needs vitamin D, B12, and zinc testing. These tests are most useful for individuals with risk factors for deficiency, such as dietary restrictions, malabsorption, or chronic illness. Testing should be guided by clinical suspicion.

Can biotin supplements mess up thyroid or other blood test results?

Yes, biotin supplements can interfere with certain blood tests, especially thyroid function tests. High biotin intake may cause inaccurate results. Inform your clinician if you are taking biotin, as you may need to pause supplementation before testing.

If my labs are normal, what could still be causing my shedding?

Even with normal lab results, telogen effluvium can occur due to triggers such as illness, stress, surgery, or childbirth. The diagnosis is based on clinical history and examination rather than lab findings alone.

How soon after starting treatment should labs be rechecked?

The timing for rechecking labs depends on the specific deficiency and treatment. Your clinician will advise when to repeat tests, as premature testing may not reflect true changes. Follow-up is typically scheduled several weeks to months after starting treatment.