If initial CT for suspected SAH is negative, which test is used to look for blood or xanthromia?

If initial CT for suspected SAH is negative, which test is used to look for blood or xanthromia?

• A. EEG
• B. Lumbar puncture
• C. MRI
• D. CT angiography

Answer: (B)

When a patient has suspected SAH but the initial CT is negative, examining the CSF with a lumbar puncture is the test to look for signs of bleeding. CT scans catch most acute SAH, but their sensitivity drops after the first several hours, so a negative CT doesn’t completely rule out SAH if symptoms persist or timing is later. Lumbar puncture allows you to detect blood in the CSF and, more importantly, xanthochromia, which is a yellow discoloration from bilirubin formed as red blood cells break down in the CSF. Xanthochromia typically appears hours after the bleed and can linger for days, providing a reliable clue that SAH occurred even when the CT was negative. In practice, clinicians also compare red blood cell counts across sequential CSF tubes to help distinguish true SAH from a traumatic tap, since a traumatic tap usually shows decreasing RBCs in later tubes whereas SAH often yields a consistent RBC count or xanthochromia.

When a patient has suspected SAH but the initial CT is negative, examining the CSF with a lumbar puncture is the test to look for signs of bleeding. CT scans catch most acute SAH, but their sensitivity drops after the first several hours, so a negative CT doesn’t completely rule out SAH if symptoms persist or timing is later.

Lumbar puncture allows you to detect blood in the CSF and, more importantly, xanthochromia, which is a yellow discoloration from bilirubin formed as red blood cells break down in the CSF. Xanthochromia typically appears hours after the bleed and can linger for days, providing a reliable clue that SAH occurred even when the CT was negative. In practice, clinicians also compare red blood cell counts across sequential CSF tubes to help distinguish true SAH from a traumatic tap, since a traumatic tap usually shows decreasing RBCs in later tubes whereas SAH often yields a consistent RBC count or xanthochromia.