Blood Tests for Hair Loss
Losing hair? Before you spend hundreds on shampoos and supplements, a blood test can reveal whether the cause is hiding in your iron levels, thyroid, or hormones.
Why Blood Tests Matter for Hair Loss
Hair loss is one of the most distressing symptoms people experience, yet its causes are frequently internal and invisible. Your hair follicles are metabolically demanding structures - they are the second-fastest dividing cells in your body (after bone marrow). When your body is low on key nutrients or hormones are out of balance, hair is the first thing it sacrifices.
The problem is that most GPs only check TSH and ferritin when investigating hair loss. While these are important, they miss several common causes. A comprehensive panel of 8 tests can identify the vast majority of treatable, internal causes of hair loss.
Perhaps most importantly, there is a crucial difference between “normal” lab ranges and “optimal” levels for hair growth. Your ferritin might be 20 μg/L - technically normal - but dermatologists know that hair regrowth typically requires levels above 70 μg/L. Understanding this distinction is key to getting the right treatment.
The 8 Essential Blood Tests for Hair Loss
1. Ferritin (Stored Iron)
Why it matters for hair: Ferritin is the single most important blood test for hair loss. Your hair follicles are among the most rapidly dividing cells in your body and they need a steady supply of iron to grow. When ferritin drops, your body prioritises vital organs over hair - your follicles are the first to be starved of iron, pushing them prematurely into the resting (telogen) phase.
Optimal for hair growth: Most labs flag ferritin as "normal" above 15-20 µg/L. However, dermatologists and trichologists consistently report that hair regrowth typically requires ferritin above 70 µg/L, and ideally above 80 µg/L. A ferritin of 25 is "normal" on paper but can absolutely cause hair loss.
Watch out: Ferritin is an acute-phase reactant - it rises during inflammation and infection. If you have been unwell recently, your ferritin may appear falsely normal. Ask your doctor to also check CRP (inflammation marker) alongside ferritin.
2. Thyroid Panel (TSH, FT4, FT3)
Why it matters for hair: Thyroid hormones regulate the hair growth cycle at a cellular level. Hypothyroidism (underactive thyroid) causes diffuse thinning across the entire scalp, dry and brittle hair that breaks easily, and loss of the outer third of the eyebrows - a classic clinical sign. Hyperthyroidism (overactive thyroid) causes fine, thin hair that does not hold a style. Both conditions can also cause excessive hair shedding.
Optimal for hair growth: For hair health, optimal TSH is between 1.0 and 2.5 mIU/L. Many labs use a reference range of 0.4-4.0, but a TSH of 3.5 - while technically "normal" - may already be slowing your hair growth. Free T4 should be in the upper half of the reference range.
Watch out: TSH alone is not enough. Some people have "normal" TSH but low Free T3, which is the active hormone that actually drives hair growth. Always request the full panel: TSH, Free T4, and Free T3.
3. Vitamin D (25-OH)
Why it matters for hair: Vitamin D plays a critical role in the hair follicle cycle. It stimulates the creation of new hair follicles and helps maintain the anagen (growth) phase. Research has shown that vitamin D receptors in hair follicles are essential for normal hair cycling, and deficiency is strongly linked to telogen effluvium (excessive shedding) and alopecia areata (patchy hair loss).
Optimal for hair growth: Aim for at least 75 nmol/L (30 ng/mL). Levels below 50 nmol/L are associated with increased hair shedding. In Australia, over 30% of adults are vitamin D deficient despite our sunny climate - sunscreen use, indoor work, and darker skin tones all increase the risk.
Watch out: Vitamin D testing is bulk billed in Australia when there is a clinical indication (fatigue, bone pain, limited sun exposure, or documented deficiency). Hair loss qualifies as a clinical indication in most cases.
4. Zinc
Why it matters for hair: Zinc is essential for DNA and RNA production, cell division, and protein synthesis - all processes that hair follicles depend on heavily. It also helps maintain the oil glands around follicles. Zinc deficiency disrupts the structural integrity of hair proteins (keratin), leading to weak hair that breaks and falls out. Vegetarians and vegans are at particular risk because plant-based zinc is less bioavailable.
Optimal for hair growth: Serum zinc should be above 11 µmol/L. Levels between 8-11 µmol/L are considered insufficient for optimal hair growth, even if they fall within the lab reference range. Zinc is best tested fasting in the morning.
Watch out: Zinc and iron compete for absorption. If you are supplementing both, take them at different times of day. Also, excess zinc (above 40 mg/day from supplements) can actually cause copper deficiency, which itself causes hair loss.
5. Vitamin B12
Why it matters for hair: Vitamin B12 is required for red blood cell formation and DNA synthesis in hair follicle cells. Deficiency leads to reduced oxygen delivery to the scalp and impaired cell division. The result is diffuse hair thinning that often presents with other neurological symptoms like tingling, numbness, and brain fog. B12 deficiency is common in vegans and vegetarians (B12 is almost exclusively found in animal products), elderly people (reduced absorption), and those taking metformin or proton pump inhibitors.
Optimal for hair growth: Serum B12 above 300 pmol/L is ideal. Levels between 150-300 pmol/L are a grey zone where symptoms often occur. If your B12 is in this range and you have hair loss, consider testing Active B12 (holotranscobalamin), which is a more sensitive marker of true B12 status.
Watch out: Standard serum B12 can be falsely elevated in liver disease and myeloproliferative disorders. Active B12 is the more reliable test but is not always bulk billed.
6. Sex Hormones
Why it matters for hair: Androgenetic alopecia (pattern hair loss) is driven by hormones, specifically the conversion of testosterone to dihydrotestosterone (DHT) by the enzyme 5-alpha reductase. DHT shrinks hair follicles in genetically susceptible areas. In women, elevated testosterone from conditions like Polycystic Ovary Syndrome (PCOS) is a common cause. SHBG (Sex Hormone Binding Globulin) regulates how much free testosterone is available to convert to DHT.
Optimal for hair growth: For women: total testosterone below 2.0 nmol/L, DHEA-S within age-appropriate range. Low SHBG means more free testosterone available, which increases DHT-mediated hair loss. For men: elevated DHT relative to testosterone suggests high 5-alpha reductase activity.
Watch out: In women, always test sex hormones in the early follicular phase (days 2-5 of the menstrual cycle) for accurate results. Random-day testing can give misleading values. Also request SHBG - it is often omitted but critical for interpreting free testosterone levels.
7. ANA (Antinuclear Antibodies)
Why it matters for hair: ANA screening checks for autoimmune conditions that cause hair loss. Alopecia areata (patchy hair loss) is an autoimmune condition where your immune system attacks hair follicles. Systemic lupus erythematosus (SLE) causes a distinctive pattern of scarring hair loss along the hairline and temples. Hashimoto thyroiditis, another autoimmune condition, causes diffuse thinning. A positive ANA does not diagnose a specific condition but flags the need for further investigation.
Optimal for hair growth: ANA should be negative (or below 1:40 titre). A positive result at 1:80 or higher warrants further testing with specific antibody panels depending on clinical presentation.
Watch out: Low-positive ANA results (1:40 to 1:80) are common in healthy people - up to 15% of the population may have a low-positive ANA with no autoimmune disease. Context matters more than the number alone.
8. HbA1c / Fasting Glucose
Why it matters for hair: Diabetes and insulin resistance damage small blood vessels that supply hair follicles, reducing nutrient and oxygen delivery to the scalp. Chronically elevated blood sugar also triggers systemic inflammation and hormonal imbalances that accelerate hair loss. People with uncontrolled diabetes frequently report diffuse thinning and slower hair regrowth. Insulin resistance (pre-diabetes) can also worsen androgenetic alopecia by increasing free testosterone levels.
Optimal for hair growth: HbA1c below 5.7% (39 mmol/mol) is normal. Between 5.7-6.4% (39-47 mmol/mol) indicates pre-diabetes and may already be affecting hair growth. Fasting glucose should be below 5.5 mmol/L.
Watch out: HbA1c reflects your average blood sugar over 3 months - it is not affected by what you ate yesterday. This makes it a more reliable marker than a single fasting glucose reading, which can vary day to day.
Male vs Female Hair Loss Patterns
Hair loss presents differently in men and women, and the underlying causes often differ too. Understanding your pattern helps guide which blood tests to prioritise.
| Factor | Female Pattern | Male Pattern |
|---|---|---|
| Typical pattern | Diffuse thinning, widening part line | Receding hairline, crown thinning |
| Key hormones to test | Testosterone, DHEA-S, Oestradiol, SHBG | DHT, Testosterone, SHBG |
| Most common cause | Iron deficiency, thyroid, PCOS | Genetics (androgenetic alopecia), DHT |
| Additional tests | FSH, LH, Prolactin, Insulin | DHT, PSA (if considering finasteride) |
| Age of onset | Any age, peaks post-menopause | Often starts in 20s-30s |
| Reversibility | Often highly reversible with treatment | Slowed/stabilised, harder to regrow |
“Normal” vs Optimal Ranges for Hair Growth
This is the most important table on this page. Lab reference ranges are designed to flag disease, not optimise health. Your results might be “within range” yet still too low for your hair follicles to thrive. Here is what dermatologists and trichologists actually aim for.
| Marker | Lab “Normal” | Optimal for Hair | Note |
|---|---|---|---|
| Ferritin | 15-200 µg/L | >70 µg/L | Most important marker for hair |
| Vitamin D | >50 nmol/L | >75 nmol/L | Below 50 strongly linked to shedding |
| Vitamin B12 | 150-750 pmol/L | >300 pmol/L | Grey zone 150-300 often symptomatic |
| Zinc | 8-23 µmol/L | >11 µmol/L | Test fasting for accuracy |
| TSH | 0.4-4.0 mIU/L | 1.0-2.5 mIU/L | Upper "normal" may still cause thinning |
| Free T4 | 10-20 pmol/L | Upper half of range | Low-normal FT4 may impair hair cycling |
These optimal ranges are based on published trichology research and clinical dermatology guidelines. Individual targets may vary - discuss your specific situation with your doctor.
What to Do With Your Results
Once you have your blood test results, here is a practical framework for next steps based on what you find.
Low Ferritin (below 70)
This is the most common treatable cause. Your GP may recommend oral iron supplements (take with vitamin C on an empty stomach for best absorption) or IV iron infusions for faster results. Retest after 3 months. Hair regrowth typically begins 6-12 months after ferritin reaches optimal levels.
Thyroid Abnormality
If TSH is above 2.5 with hair loss symptoms, discuss treatment options with your doctor. Even "subclinical" hypothyroidism (TSH 4-10 with normal FT4) can cause hair loss. Thyroid medication typically stops the shedding within 2-3 months, with regrowth visible by 6 months.
Low Vitamin D
Supplement to bring levels above 75 nmol/L. In Australia, your GP can advise on dosing (typically 1000-4000 IU daily depending on deficiency severity). Retest after 3 months. Combine with sensible sun exposure (10-15 minutes of midday sun on arms and face).
Hormonal Imbalance
Elevated testosterone or low SHBG in women may warrant referral to an endocrinologist or dermatologist. Treatment options include anti-androgen medications (spironolactone), oral contraceptives, or topical treatments. Men may discuss finasteride or dutasteride with their doctor.
When to See a Doctor Urgently
Most hair loss is gradual and not an emergency. However, certain patterns warrant prompt medical attention:
Sudden loss of large clumps of hair over days
Circular bald patches appearing rapidly (alopecia areata)
Scalp redness, pain, or scarring with hair loss
Hair loss accompanied by significant weight loss, fatigue, or joint pain
Hair loss after starting a new medication
Hair loss with skin rash (especially a butterfly rash on the face)
Related Reading
Upload Your Results - Check Your Hair Health Markers
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SmarterBlood provides educational health information. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your doctor or other qualified health provider with any questions you may have regarding hair loss or other medical conditions.