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The diagnosis of cluster headache is usually based strictly on clinical symptoms. In most individuals there is no underlying cause of cluster (vascular malformation, tumor) so that diagnostic testing is typically normal and the clinical picture is so clear that there is no question about the diagnosis.

Sometimes, the diagnosis can be difficult to obtain since some symptoms of cluster headache may be common to many other conditions. In this case, some physicians may try to induce an attack by administering nitroglycerin. The symptoms can then be observed and evaluated while they are occurring.

Tests that a physician may consider include:

• An MRI of the brain to rule out a tumor, stroke, or vascular malformations
• A sleep study, since there is recent evidence that many cluster patients have obstructive sleep apnea. Once the sleep apnea is treated, some cluster headache patients see great improvement in their headaches.
• Electrocardiogram (ECG) - One of the best abortive therapies for cluster headache is a sumatriptan injection. Only patients without cardiac involvement can use this drug so an ECG is necessary to rule-out cardiac conditions such as past heart attacks.
• Blood laboratory evaluation - generally blood work is not needed for diagnosis of cluster headaches.

Another diagnostic aid in confirming the diagnosis of cluster headache is when consumption of minimal amounts of alcohol induces a headache attack within minutes while the patient is in the midst of a cluster episode. It is a highly typical response among individuals with cluster headache, but its absence does not negate a diagnosis of cluster headache.