Neuroligical Emergencies—How do you make sure you're dealing with a SAH?

The best first test is a CT of the head without contrast. You look for subarachnoid blood ( a good example lives in our our "angiograms annotated for med students" archive).

If the CT scan is diagnostic, your diagnosis is made. Call the neurosurgeon now.

But what happens if the CT is negative? I.E. can you have a real SAH with a negative CT scan? Most certainly, fair physician, because it takes about 50,000 RBC/cc to opacify CSF.

So if you have a screamingly classic history and a NEGATIVE CT scan, what do you do?

You forge on. Next step is to do a lumbar puncture (yes, right there in the ER and yes, right NOW). Send tubes 1 and 4 for cell counts and compare.

Spin the fluid down and look for yellow coloration of the supernatant. If the supernatant is yellow (i.e. "anthochromia") or tubes 1 and 4 have about equal RBC counts, you have a subarachnoid hemorrhage. If the LP is negative, tell the patient to try harder next time...