MSFinals-6371

You are working as a locum on the paediatric neurosurgical unit. Three of the patients seen on the ward round have subarachnoid haemorrhages. Your consultant wants blood tests on all of them, but forgets to tell you which ones. All three patients are stable. Their aneurysms are secured and they will be discharged in a few days time. Which single blood test is most valuable in these patients?