<prompt> Initial Investigation of choice of subarachnoid hemorrhage: March 2009AngiographyLumbar punctureCT scanSerum electrolytes  <response>: Ans. C: CT scan Investigations: Full blood count -- anaemia sickle cell disease, leucocytosis after a seizure, systemic infection Coagulation screen -- underlying coagulopathy Urea and electrolytes -- hyponatraemia is common after subarachnoid haemorrhage due to salt wasting, not inappropriate antidiuretic hormone secretion Serum glucose -- hypoglycaemia needs correction,hyperglycaemia is associated with poor outcome after subarachnoid haemorrhage Serum magnesium -- hypomagnesaemia is common and associated with poor outcome after subarachnoid haemorrhage Chest radiography -- pulmonary oedema, aspiration Twelve lead electrocardiography -- cardiac arrhythmia, ST segment changes,myocardial stunning Unenhanced computed tomography of the brain--as soon as possible after onset of headache 24 hours. More than 95 of cases can be diagnosed on high quality non-contrast CT scan obtained within 72 hours. Lumbar puncture--if an unenhanced computed tomogram of the brain is normal Computed tomography angiography-- if subarachnoid haemorrhage is confirmed by computed tomography or lumbar puncture. 