When to order laboratory tests for your patient with a headache

Laboratory tests for patients with headache may be helpful under certain circumstances. A complete blood count (CBC), thyroid function, and erythrocyte sedimentation rate (ESR) are basic tests that are helpful in evaluating some headache patients.

A basic metabolic panel should include glucose, electrolyte and fluid balance, and kidney function. This panel usually measures the blood levels of blood urea nitrogen (BUN), calcium, carbon dioxide, chloride, creatinine, glucose, potassium, and sodium.

Hypothyroidism or hyperthyroidism may be associated with headaches.

ESR is used to assess for possible giant cell arteritis. Individuals over the age of 50 with new onset headache should have their ESR and / or C-reactive protein (CRP) levels checked to exclude temporal arteritis.

Patients with arthralgias and headache should be considered for antinuclear antibody (ANA) and rheumatoid factor (RF) as well. Don’t forget to test for mononucleosis in a teen with a headache, adenopathy, and fever. When infection is a concern, HIV and Lyme antibodies should be tested for.

Perform a lumbar puncture when infection or subarachnoid hemorrhage is suspected. Red cell counts performed on the first and last tubes can help differentiate a traumatic tap. The cell count will usually dramatically fall in trauma but not in subarachnoid hemorrhage. Look for xanthochromia in spun samples several hours after a subarachnoid hemorrhage. This is preferably done with spectrophotometry, which further increases sensitivity.

Measuring the opening pressure is essential to diagnose intracranial hypertension or pseudotumor cerebri. All pressure measures should be undertaken with the patient in the lateral decubitus position with legs extended, not prone or sitting. Pressures > 250 mmH₂O are deemed elevated.

In infection, examining the cerebrospinal fluid for white cell count with differential, and glucose, is essential. Cerebrospinal fluid glucose must be compared to serum glucose.

An electroencephalogram, or EEG, is not considered useful in the evaluation of headache unless there are concomitant considerations present to consider epilepsy in the diagnosis, such as with atypical migraine aura or recurrent loss or clouding of consciousness. Therefore, EEG is not recommended to rule out structural lesions when MRI or CT are readily available.

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