Initial diagnostic test for suspected subarachnoid hemorrhage?

• A. Noncontrast head CT
• B. Lumbar puncture
• C. MRI
• D. Angiography

Answer: (A)

When subarachnoid hemorrhage is suspected, the first test to obtain is a noncontrast head CT. Blood in the subarachnoid space appears as a hyperdense material on CT, and this study can rapidly confirm acute bleeding without needing contrast. Its sensitivity is highest in the first hours after onset, making it the fastest and most efficient way to diagnose an SAH in an emergency setting.

If the CT is negative but clinical suspicion remains high, a lumbar puncture is performed to look for red blood cells in CSF or for xanthochromia, which can indicate subarachnoid blood that CT missed. MRI can detect SAH but is not as quick or reliably sensitive in the acute phase. Angiography, including CT angiography or digital subtraction angiography, is used after SAH is confirmed to locate an aneurysm or other vascular source, guiding definitive treatment.