Blood culture (x2)

Lumbar puncture (if not contraindicated: see text)

Throat swab (request culture for meningococci)

Full blood count

EDTA sample for PCR (for meningococci and pneumococci) – especially if blood cultures drawn after antibiotic therapy

Coagulation screen if there is petechial or purpuric rash or low platelet count

C-reactive protein

Blood glucose (for comparison with CSF glucose)

Creatinine and electrolytes

Arterial blood gases, pH and lactate

Chest X-ray (pneumonia or lung abscess?)

Skull X-ray if suspected sinus infection (nasal discharge, sinus tenderness) or skull fracture

CT if suspected intracranial mass lesion or skull X-ray abnormal