What basic blood work is recommended for a patient presenting with a headache, considering their age, medical history, and potential underlying conditions such as hypertension, diabetes, or neurological disorders?

Basic Blood Work for Headache

Routine blood work is generally not indicated for patients presenting with headache who have a normal neurological examination and no red flag features. 1, 2

When Blood Tests Are NOT Needed

The diagnostic evaluation of headache relies primarily on clinical history and physical examination, not laboratory testing. 1, 3 Most primary headache disorders (migraine, tension-type headache, cluster headache) are diagnosed using clinical criteria defined by the International Headache Society and do not require blood work. 4, 1

In patients with a normal neurological examination and no concerning features, blood tests add no diagnostic value and should be avoided. 1, 5

Specific Blood Tests for Red Flag Scenarios

Blood work becomes appropriate only when specific secondary causes are suspected based on clinical features:

Giant Cell Arteritis (Age >50 Years)

• ESR and CRP should be obtained if the patient is over 50 years old with new-onset headache, scalp tenderness, or jaw claudication. 1, 6
• Important caveat: ESR can be normal in 10-36% of giant cell arteritis cases, so clinical suspicion should guide referral to rheumatology even with normal values. 1

Thyroid Dysfunction

• Morning TSH and free T4 are indicated only if the patient has cold intolerance or lightheadedness suggesting hypothyroidism. 1
• Thyroid peroxidase (TPO) antibodies should be checked if biochemical hypothyroidism is confirmed. 1

Red Flags That Warrant Investigation (But Not Necessarily Blood Work)

The following features suggest secondary headache and require evaluation, though typically with neuroimaging rather than blood tests:

• Thunderclap headache (sudden severe onset) 1, 6
• Progressive worsening over weeks to months 1, 6
• Headache awakening patient from sleep 1, 6
• Worsening with Valsalva maneuver, coughing, or exertion 1, 6
• New-onset headache after age 50 1, 6
• Focal neurological symptoms or signs 1, 6
• Unexplained fever or neck stiffness (suggests meningitis) 1, 6
• Altered consciousness, memory, or personality 1, 6

Algorithmic Approach

1. Perform thorough neurological examination first - this determines all subsequent testing 1, 5

2. If examination is normal AND no red flags present:

   • No blood work needed 1, 5
   • Diagnose based on clinical criteria (migraine, tension-type, cluster) 1

3. If patient is >50 years with new-onset headache:

   • Check ESR/CRP for giant cell arteritis 1, 6
   • Refer to rheumatology if clinical suspicion remains high despite normal values 1

4. If symptoms suggest hypothyroidism (cold intolerance, lightheadedness):

   • Check morning TSH and free T4 1
   • Add TPO antibodies if hypothyroidism confirmed 1

5. If any red flags present:

   • Prioritize neuroimaging (MRI brain with/without contrast preferred) over blood work 1, 5
   • Consider emergency admission if patient unable to self-care or has thunderclap headache 1

Common Pitfalls to Avoid

• Do not order "routine" blood work panels - they have no diagnostic yield in primary headache disorders and may lead to false positive results requiring unnecessary follow-up. 1, 5

• Do not rely on blood tests to exclude serious pathology - neuroimaging (MRI or CT) is the appropriate test for structural causes, not laboratory studies. 1, 2

• Do not forget medication-overuse headache - this is the most common secondary cause in patients with worsening headaches and is diagnosed clinically (≥10 days/month of acute medication use for ≥3 months), not with blood tests. 1, 6