What Blood Tests Help with Headaches — and What They Can't Find

Let us start with the honest answer that rarely makes the first screen: there is no lab test "for headache". Migraine, tension-type and cluster headaches are clinical diagnoses: they are made from the history, a diary and an examination, and no line on a blood form confirms or excludes them. Why test at all, then? Because headaches have secondary causes and "amplifiers" — anaemia, inflammation, thyroid dysfunction — and those the lab catches well. Here is what makes sense to test, what does not, and when the right move is an examination and MRI instead of the lab.

What tests can and cannot do

Headache is an umbrella diagnosis: behind the code R51 hide dozens of different conditions. Primary headaches — migraine (G43), tension-type — are invisible to the lab entirely. What tests do well is two other jobs: ruling out systemic causes (inflammation, infection, endocrine disorders) and finding conditions that make any headache more frequent and more severe — iron deficiency, anaemia, glucose problems. So the correct formula is: labs in headache are not a search for the diagnosis but a check of the background.

The sensible panel: six directions

This panel takes one fasting morning visit and covers the vast majority of "laboratory" causes. Ordering dozens of extra markers without a doctor is money wasted: the chance of a random borderline finding grows faster than the chance of a useful one.

After 50 — the special case: ESR and CRP urgently

There is one situation where a blood test for headache is needed urgently rather than routinely: a first-ever headache in a person over 50, especially in the temples, with scalp tenderness, jaw pain on chewing or visual disturbance. That is the picture of giant cell (temporal) arteritis — an artery inflammation in which ESR and CRP rise sharply. Delay risks irreversible vision loss, so with this suspicion the doctor orders the tests the same day and does not wait for an MRI slot. The diagnosis is rare, but it is exactly what makes the "ESR + CRP" pair mandatory in the panel for people over 50.

When you need an examination and MRI, not labs

Red flags where the laboratory is the wrong first stop:

• a thunderclap headache — peak intensity within seconds to minutes ("the worst pain of my life");
• headache with neurological symptoms: limb weakness, facial droop, slurred speech, double vision, confusion;
• a first-ever headache after 50;
• pain building week by week, or worse when lying down, coughing or straining;
• headache with fever and a stiff neck;
• a change in the usual pattern in someone with cancer or a weakened immune system.

These cases need a neurologist's examination today, and the imaging method — MRI or CT — is the doctor's choice. Blood tests exclude nothing here and only lose time.

The headache diary — the one "test" no lab performs

For a primary headache diagnosis, what the doctor needs most is a 4-week diary: date, start and end time, intensity out of 10, character (throbbing/pressing), side, what preceded it (sleep, food, stress, cycle), what was taken and whether it helped. Such a diary separates migraine from tension-type headache more precisely than any biochemical panel — and immediately exposes painkiller overuse, itself a frequent cause of chronic daily headache (medication-overuse headache). Phone notes are fine — regularity matters, not the format.

Sleep, caffeine and blood pressure: the modifiers worth checking

Three everyday factors change the headache picture more than most lab tests:

• Sleep. Both sleep debt and weekend oversleeping are classic triggers; chronic sleep shortage turns pain into a daily one. Estimate your personal norm in the sleep calculator.
• Caffeine. Works both ways: excess provokes pain, and abruptly dropping a habitual dose brings a 1–2-day withdrawal headache.
• Blood pressure. Contrary to the myth, moderate hypertension rarely hurts — but sharp spikes and crises do. If headaches come with high cuff readings, start with the panel from the guide to tests for hypertension.

A separate storyline is headache with dizziness — that pair has its own list of causes, covered in the article on causes of dizziness. And if the pain travels together with constant tiredness, compare your picture with the guide to causes of weakness and fatigue.

The short version

Blood tests do not diagnose a headache — they check the background: CBC, ESR and CRP, glucose, TSH, ferritin, electrolytes. After 50, a new headache means ESR and CRP the same day; red flags mean an examination and MRI, not the lab; a month of diary beats any form. The diagnosis is the doctor's — and ready results can be uploaded for decoding: the service explains every value and helps you assemble questions for the neurologist.