What initial bloodwork is recommended for a patient presenting with new onset headache?

Initial Bloodwork for New Onset Headache

For patients presenting with new onset headache, obtain ESR and C-reactive protein to screen for temporal arteritis in patients over 50, along with basic metabolic panel, complete blood count, and blood pressure measurement to identify systemic causes, though imaging rather than bloodwork drives the diagnostic evaluation for most life-threatening secondary headaches. 1, 2

Age-Specific Bloodwork Priorities

Patients Over Age 50

• ESR and C-reactive protein are mandatory in all patients over 50 with new headache to screen for temporal arteritis (giant cell arteritis), though ESR can be normal in 10-36% of biopsy-proven cases 1, 3
• The American College of Rheumatology emphasizes this testing because temporal arteritis affects 60-90% of patients with this condition through headache, and delayed diagnosis risks permanent vision loss 1, 3
• Blood pressure measurement is essential as part of immediate assessment, since hypertensive emergency can present as new headache 1, 4

All Age Groups

• Complete blood count (CBC) to identify infection, anemia, or hematologic malignancy 2, 4
• Basic metabolic panel to detect electrolyte abnormalities, renal dysfunction, or metabolic derangements 2, 4
• Blood glucose to exclude hypoglycemia or hyperglycemia as headache triggers 4

Red Flag Features Requiring Additional Testing

Systemic Signs Present

• If fever, weight loss, or malaise accompany headache, obtain inflammatory markers (ESR, CRP), blood cultures if febrile, and consider HIV testing in appropriate risk populations 2, 3
• Pregnancy test in women of childbearing age, as pregnancy substantially alters the differential diagnosis and management 2

Cancer or Immunosuppression History

• In patients with known cancer or immunosuppression, obtain CBC with differential, comprehensive metabolic panel, and consider coagulation studies 2, 5
• These patients require more aggressive investigation as they have higher risk of metastatic disease, opportunistic infections, and medication-related complications 2, 3

Critical Algorithmic Approach

Step 1: Vital signs and basic screening

• Blood pressure, temperature, heart rate 1, 2
• If patient >50 years: ESR and CRP mandatory 1, 3

Step 2: Risk stratification bloodwork

• CBC, basic metabolic panel for all patients with concerning features 2, 4
• Pregnancy test for women of childbearing age 2
• Blood cultures if febrile 2

Step 3: Recognize imaging takes priority

• Bloodwork does NOT exclude subarachnoid hemorrhage, brain tumor, or other structural causes 6, 1, 2
• Non-contrast head CT must be obtained within 6 hours for thunderclap headache (98.7% sensitivity for SAH) 1, 6
• Lumbar puncture with spectrophotometric xanthochromia analysis (100% sensitivity) required if CT negative but clinical suspicion high for SAH 1, 6

Common Pitfalls to Avoid

• Do not rely on normal ESR to exclude temporal arteritis in patients over 50, as 10-36% of biopsy-proven cases have normal ESR 1, 3
• Do not assume bloodwork can substitute for neuroimaging when red flags are present—structural causes require imaging, not laboratory evaluation 2, 5
• Do not delay imaging to wait for laboratory results in patients with thunderclap headache, focal neurological deficits, or altered mental status 6, 1, 2
• Normal bloodwork does not exclude serious secondary headache disorders; the history and examination determine imaging needs, not laboratory values 2, 5, 4

When Bloodwork Is Insufficient

Neuroimaging (MRI preferred, CT if acute) is indicated regardless of bloodwork results when patients have: 2, 5

• Thunderclap or "first/worst" headache 6, 1
• Progressive or worsening headache pattern 2, 7
• Neurological deficits on examination 2, 5
• Age over 50 with new headache (after obtaining ESR/CRP) 1, 3
• Headache triggered by Valsalva, cough, or exertion 2
• Recent head or neck trauma 2, 3