Blood Tests for Headaches & Migraines
8 blood markers that reveal hidden, treatable causes of chronic headaches. Your pain might have a fixable deficiency behind it.
Why Blood Tests Matter for Headache Sufferers
Most headache patients are told it is “just stress” or “just migraines” without any blood work. Yet research consistently shows that nutritional deficiencies, hormonal imbalances, and chronic inflammation are treatable causes of headaches that a simple blood test can identify.
A 2020 study in the Journal of Headache and Pain found that over 40% of chronic headache patients had at least one correctable blood test abnormality. The most common: low ferritin, low magnesium, low vitamin D, and subclinical thyroid dysfunction. Fixing these deficiencies reduced headache frequency by 50% or more in the majority of patients.
The 8 Blood Tests Your Doctor Should Order
1. Iron Studies & Ferritin
Why this matters: Iron deficiency is one of the most overlooked causes of chronic headaches, particularly in women of reproductive age. When your ferritin drops, your red blood cells carry less oxygen to the brain. The brain is exquisitely sensitive to even mild oxygen reduction, responding with dull, persistent headaches that worsen with physical activity. Studies show that iron-deficient women are 1.5 times more likely to experience chronic headaches.
Optimal levels: Most labs flag ferritin as normal above 15–20 µg/L, but headache specialists report that patients often find relief once ferritin rises above 50 µg/L. For migraine sufferers, aim for ferritin above 70 µg/L. Haemoglobin should be above 130 g/L for men and 120 g/L for women.
Watch out: Ferritin rises during inflammation and infection (it is an acute-phase reactant). If you have been unwell, your ferritin may look normal despite true iron deficiency. Always check CRP alongside ferritin to rule out falsely elevated results.
2. Magnesium (Serum & RBC)
Why this matters: Magnesium is arguably the single most important mineral for migraine prevention. It regulates neurotransmitter signalling, controls blood vessel tone, and modulates the brain’s electrical activity. Low magnesium allows excessive glutamate release and cortical spreading depression — the wave of brain activity that triggers migraine aura. The American Headache Society and the Canadian Headache Society both recognise magnesium supplementation as a Level B evidence-based migraine preventive.
Optimal levels: Serum magnesium reference range is typically 0.70–1.10 mmol/L, but this only reflects 1% of total body magnesium (the rest is inside cells). RBC magnesium is a better indicator — aim for above 1.65 mmol/L. Many migraine patients have “normal” serum magnesium but deficient RBC magnesium.
Watch out: Standard blood tests only measure serum magnesium, which is the least sensitive measure. Ask specifically for RBC (red blood cell) magnesium. If unavailable, trial 400mg magnesium glycinate daily for 3 months — this is safe and evidence-based even without testing.
3. Thyroid Panel (TSH, FT4, FT3)
Why this matters: Both hypothyroidism and hyperthyroidism cause headaches through different mechanisms. An underactive thyroid leads to fluid retention and increased intracranial pressure, producing dull, constant headaches often worse in the morning. An overactive thyroid causes blood vessel dilation and pounding, throbbing headaches. Up to 30% of people with hypothyroidism report frequent headaches, and thyroid disorders are significantly more common in migraine patients than the general population.
Optimal levels: For headache patients, optimal TSH is 1.0–2.5 mIU/L. A TSH of 3.5 is technically “normal” but may already be contributing to your headaches. Free T4 should be in the upper half of the reference range. Free T3 is the active hormone — it should not be in the bottom quarter.
Watch out: Thyroid antibodies (TPO, TG) can cause headaches even when TSH is still normal. If you have a family history of thyroid disease or autoimmune conditions, ask for antibody testing alongside the standard panel.
4. Vitamin D (25-OH)
Why this matters: Vitamin D receptors are found throughout the brain and blood vessels, and deficiency is strongly associated with increased headache frequency. A large meta-analysis published in the Journal of Headache and Pain found that vitamin D deficiency doubles the risk of chronic headaches. Vitamin D also modulates inflammation — and neuroinflammation is a key driver of migraine pathophysiology.
Optimal levels: Aim for at least 75 nmol/L (30 ng/mL), with some headache specialists recommending 100–150 nmol/L for migraine prevention. In Australia, over 30% of adults are deficient despite the sunny climate. Indoor workers, people with darker skin tones, and those using sunscreen consistently are at highest risk.
Watch out: Vitamin D testing is Medicare bulk-billed in Australia when there is a clinical indication. Chronic headaches qualify. Supplementation dosing depends on your current level — severe deficiency may need a loading dose before maintenance.
5. Vitamin B12 & Folate
Why this matters: B12 and folate are essential for nerve function, myelin production, and the methylation cycle. Deficiency causes elevated homocysteine — an amino acid that damages blood vessel walls and triggers inflammatory headaches. B12 deficiency also impairs the production of serotonin and nitric oxide, both critical neurotransmitters in migraine. Vegans, vegetarians, and people on metformin or proton pump inhibitors (PPIs) are at particularly high risk.
Optimal levels: B12 should be above 300 pmol/L (many labs use a lower cutoff of 150 pmol/L, which only catches severe deficiency). Active B12 (holotranscobalamin) is a more sensitive marker — aim for above 50 pmol/L. Folate should be above 20 nmol/L. Homocysteine should be below 10 µmol/L.
Watch out: Standard B12 testing can miss functional deficiency. If your B12 is in the “grey zone” (150–300 pmol/L) and you have neurological symptoms, ask for active B12 (holotranscobalamin) or methylmalonic acid (MMA) for a definitive answer.
6. CRP & ESR (Inflammation)
Why this matters: Chronic inflammation is a major contributor to persistent headaches and migraine frequency. Elevated CRP indicates systemic inflammation, which sensitises pain pathways in the brain. In temporal arteritis (giant cell arteritis), dramatically elevated ESR is a diagnostic hallmark — this condition causes severe, new-onset headaches in people over 50 and is a medical emergency that can lead to permanent vision loss if untreated.
Optimal levels: CRP should be below 3 mg/L. High-sensitivity CRP (hs-CRP) provides finer resolution — ideally below 1.0 mg/L for cardiovascular and neurological health. ESR should be below 20 mm/hr for men under 50, and below 30 mm/hr for women under 50.
Watch out: If you are over 50 and experience NEW severe headaches (especially with jaw pain, scalp tenderness, or visual changes), this is a medical emergency. ESR and CRP should be tested urgently to rule out giant cell arteritis. Do not wait for a routine appointment.
7. Full Blood Count (FBC)
Why this matters: A full blood count reveals anaemia (low haemoglobin), polycythaemia (high haemoglobin), and infection — all of which cause headaches. Anaemia reduces oxygen delivery to the brain. Polycythaemia thickens the blood, slowing circulation and causing pressure headaches. An elevated white cell count suggests infection or inflammation. Even mild anaemia that is “technically normal” can cause headaches in sensitive individuals.
Optimal levels: Haemoglobin: above 130 g/L (men) and 120 g/L (women). MCV: 80–98 fL (low MCV suggests iron deficiency, high MCV suggests B12/folate deficiency). Haematocrit should be within range — elevated haematocrit above 0.50 warrants investigation.
Watch out: MCV (mean cell volume) is a powerful clue that is often overlooked. Low MCV with headaches points to iron deficiency. High MCV with headaches points to B12 or folate deficiency. Both can be present simultaneously in mixed deficiency (MCV may appear normal, masking the problem).
8. Blood Glucose & HbA1c
Why this matters: Blood sugar dysregulation is a potent migraine trigger. Both hypoglycaemia (low blood sugar) and reactive hypoglycaemia (sugar crash after a high-carb meal) cause headaches by starving the brain of glucose. The brain uses 20% of the body’s glucose despite being only 2% of body weight. Pre-diabetes and insulin resistance also drive chronic low-grade inflammation, which sensitises pain pathways. Migraine patients are twice as likely to have insulin resistance as non-migraineurs.
Optimal levels: Fasting glucose: 4.0–5.4 mmol/L (below 4.0 suggests hypoglycaemia, above 5.5 suggests pre-diabetes). HbA1c: below 5.7% (39 mmol/mol). Fasting insulin: below 10 mIU/L (elevated insulin with normal glucose suggests early insulin resistance).
Watch out: Many headache patients have normal fasting glucose but elevated fasting insulin — this is early insulin resistance and a treatable cause of headaches. Fasting insulin is not routinely tested but can be requested. Dietary changes (reducing refined carbohydrates) often dramatically reduce headache frequency.
Which Tests for Which Headache Type?
Different headache types have different underlying drivers. This table maps common headache patterns to the most relevant blood tests.
| Headache Type | Pattern | Top Tests | Urgency |
|---|---|---|---|
| Tension Headache | Band-like pressure around forehead | Magnesium, Iron, Thyroid | Routine |
| Migraine with Aura | Throbbing, one-sided, visual disturbances | Magnesium, B12, Vitamin D | Routine |
| Migraine without Aura | Throbbing, nausea, light sensitivity | Iron, Magnesium, Thyroid | Routine |
| Cluster Headache | Severe pain around one eye, tearing | Testosterone, Melatonin levels | Specialist |
| Medication Overuse | Daily dull headache, rebounds | Liver function, Kidney function | GP review |
| New Daily Persistent | Constant from a specific date | CRP, ESR, FBC, Thyroid | Urgent workup |
When to See a Doctor Urgently
Most headaches are not dangerous. However, certain “red flag” headaches require immediate medical attention:
Sudden, severe headache (“worst headache of my life”) — possible subarachnoid haemorrhage
New headache after age 50 with scalp tenderness — possible giant cell arteritis
Headache with fever, stiff neck, and rash — possible meningitis
Headache with vision changes, confusion, or weakness on one side
Headache that worsens when lying down or with coughing/straining
Headache after head trauma, even if mild
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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 headaches or migraines.