Symptom Guide

Headache

Name: Headache: Causes, Blood Tests & When to Worry | HealthReview
Creator: Suman Konda
Published: 2026-07-05

Most headaches are benign.¹ But certain patterns are warning signs of serious conditions. Know which blood tests are ordered and which symptoms need emergency care.

Written by Suman Konda, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last updated: 1 September 2026 · How we check our content

Quick answer

Most headaches are tension-type (pressing, bilateral, not worsened by activity) or migraine (pulsating, one-sided, with nausea and light sensitivity). Red flags need hospital immediately: thunderclap worst-ever headache, headache with fever and neck stiffness, after head injury, or with vision loss, weakness or speech difficulty. High blood pressure rarely causes headache except in crisis above 180/120.

Emergency red flags: go to hospital immediately if headache is:

Sudden onset: worst headache of your life (thunderclap headache)
Associated with neck stiffness, fever, or rash (possible meningitis)
Following a head injury
With new neurological symptoms: vision loss, weakness, speech difficulty
Waking you from sleep progressively worsening over days-weeks

Blood tests ordered for headache

Test	What it checks for
ESR	Very high ESR >50 in elderly: suggests giant cell arteritis (temporal arteritis)
CRP	Active inflammation: infection, vasculitis, autoimmune
CBC	Infection (high WBC), anaemia (low Hb can cause headache)
Glucose	Hypoglycaemia and very high blood sugar both cause headache
TSH	Hypothyroidism and hyperthyroidism cause headaches
Sodium	Low sodium (hyponatraemia) causes severe headache and confusion
Blood pressure check	Hypertensive headache: BP >180/120
Lumbar puncture (CSF)	If subarachnoid haemorrhage or meningitis suspected

Key points

Tension headache is the commonest (70 percent): bilateral pressing pain, not pulsating, no nausea.
Migraine is moderate to severe, usually one-sided, 4 to 72 hours, with nausea and light and sound sensitivity.
Thunderclap, worst-ever headache needs immediate hospital assessment.
Giant cell arteritis (over 50s): temporal pain, jaw pain on chewing, risk of vision loss; ESR typically above 50.
Medication overuse, painkillers more than 10 to 15 days a month, causes chronic daily headache.
Hypertension alone rarely causes headache except above 180/120.

Common headache types and their features

Tension headache (most common: 70% of headaches)

Bilateral pressing or tightening sensation, mild to moderate severity, not worsened by activity. Not pulsating. No nausea. Often related to stress, poor posture, eye strain or dehydration. Blood tests normal. Treatment: paracetamol, ibuprofen, rest, hydration.

Migraine

Moderate-to-severe pulsating pain, usually one-sided, lasting 4-72 hours. Often accompanied by nausea, vomiting, sensitivity to light (photophobia) and sound (phonophobia). May have aura (visual zig-zag lines, blind spot, tingling) before headache. Triggered by stress, hormones, certain foods (red wine, cheese, chocolate), sleep changes. Blood tests normal. Requires specific migraine treatment (triptans).

Cluster headache

Excruciating, strictly one-sided pain around one eye, with watering eye and blocked nostril on same side. Occurs in clusters over weeks, then remits for months. Predominantly affects men. Blood tests normal. Treated with high-flow oxygen and sumatriptan injection.

Giant cell arteritis (temporal arteritis)

Occurs almost exclusively in people over 50. Severe temporal (side of head) pain, jaw claudication (pain when chewing), scalp tenderness, and risk of sudden vision loss. ESR is typically extremely high (>50, often >100 mm/hr). CRP also elevated. Treated urgently with high-dose prednisolone to prevent blindness. Temporal artery biopsy confirms diagnosis.

Medication overuse headache (rebound headache)

Paradoxically, taking too many painkillers (>10-15 days per month) for headache causes chronic daily headache. All painkillers worsen it. Treatment: gradual painkiller withdrawal, preventive medication.

Blood pressure and headache

Hypertension alone rarely causes headache except at very high levels (>180/120 mmHg: hypertensive crisis). Most patients with chronic hypertension do not have headache. However, a hypertensive crisis with headache, confusion or visual changes is a medical emergency.

Questions to ask your doctor

Is my headache pattern concerning for a serious cause?
Should I have an ESR to rule out giant cell arteritis?
Do I need a brain CT or MRI?
Is medication overuse contributing to my headaches?
Should I see a neurologist?

References

Sources cited on this page. PubMed links open the original abstract.

Roberts T, Horner DE, Chu K, et al. Thunderclap headache syndrome presenting to the emergency department: an international multicentre observational cohort study. Emerg Med J. 2022;39(11):803–809. PMID 35144978 · doi:10.1136/emermed-2021-211370
Ashina M. Migraine. N Engl J Med. 2020;383(19):1866–1876. PMID 33211930 · doi:10.1056/NEJMra1915327
Perry JJ, Stiell IG, Sivilotti ML, et al. Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. BMJ. 2011;343:d4277. PMID 21768192 · doi:10.1136/bmj.d4277

Red flag headaches, the features that mandate urgent imaging

The vast majority of headaches are primary, tension-type, migraine, or cluster, and require no imaging. However, certain headache patterns signal potentially life-threatening secondary causes that require urgent investigation:

Thunderclap headache: A headache that reaches maximal severity within 60 seconds, "the worst headache of my life." Subarachnoid haemorrhage (SAH) from a ruptured cerebral aneurysm must be excluded urgently. CT head without contrast is extremely sensitive for SAH within 6 hours of headache onset, a prospective study of 953 such patients found it detected all 121 confirmed cases (sensitivity 100%, 95% CI 97.0–100%)³; if negative, lumbar puncture at 12 hours looks for xanthochromia (yellow discolouration of CSF from haemoglobin breakdown).
Progressive headache over weeks: New daily headache steadily worsening suggests raised intracranial pressure, from a space-occupying lesion (tumour, cerebral abscess, subdural haematoma), idiopathic intracranial hypertension, or hydrocephalus. Associated with morning headaches (worse on waking, improved by sitting up), vomiting, or visual obscurations.
Fever + headache + neck stiffness: Bacterial meningitis, blood cultures and lumbar puncture (if safe, CT first to exclude raised ICP preventing LP) + immediate IV antibiotics without delay for diagnostic results. Every hour of delay in bacterial meningitis treatment significantly worsens outcomes.
Headache + new neurological deficit: Focal weakness, speech disturbance, visual field loss, or unilateral sensory change with headache suggests stroke, TIA, or cerebral venous sinus thrombosis.
Temporal headache in adults over 50: New-onset headache in an older adult, especially with scalp tenderness over the temporal artery, jaw claudication, visual disturbance, or a raised ESR, giant cell arteritis (GCA) until proven otherwise. Immediate high-dose prednisolone (60–100 mg) to prevent irreversible blindness; temporal artery biopsy for confirmation.

Migraine, the mechanism and evidence-based treatment

Migraine is a complex neurovascular disorder, not simply "a bad headache."² The pathophysiology involves cortical spreading depression (a wave of neuronal and glial depolarisation moving across the cortex at 3–5 mm/minute, the electrophysiological basis of aura), followed by activation of the trigeminal-vascular system and release of CGRP (calcitonin gene-related peptide), the key pro-migraine neuropeptide. CGRP causes dilation of meningeal vessels, inflammation, and the transmission of pain signals to the brain cortex.

Treatment implications of the CGRP mechanism: triptans (5-HT1B/1D agonists, sumatriptan, rizatriptan, zolmitriptan) are the gold-standard acute treatment, working by constricting dilated meningeal vessels and blocking CGRP release. For prevention, the newest class of targeted therapies, anti-CGRP monoclonal antibodies (erenumab, fremanezumab, galcanezumab, eptinezumab), directly block CGRP or its receptor and are NICE-approved for chronic migraine (15+ headache days per month, 8+ of which are migraine).

Medical Disclaimer: This page is for general educational purposes only and does not constitute medical advice. Always consult a qualified doctor for diagnosis and treatment.