investigations

Last edited 06/2018 and last reviewed 06/2021

If the diagnosis of meningitis is suspected it is of the utmost importance that the cause is established - pyogenic meningitis has a high mortality without treatment.

The following clinical signs should be recorded in all patients with suspected bacterial meningitis or meningococcal disease:

• heart rate.
• respiratory rate.
• blood pressure.
• temperature.
• capillary refill time.
• oxygen saturation measurement

Perform a neurological assessment using the AVPU:

• Alert? (even an alert child may be very ill with septicaemia)
• Responds to Voice?
• Responds to Pain?
• Unresponsive? (1)

Laboratory investigations in patients with suspected meningitis include:

• blood cultures - ideally should be done before antibiotics
• full blood count, urea, creatinine, electrolytes, liver function tests and clotting screen
• procalcitonin (or CRP if unavailable)
• useful in differentiating bacterial and viral infection
• there is insufficient evidence for routine use
• meningococcal and pneumococcal PCR
• serology sample
• glucose
• a swab of the posterior nasopharyngeal wall – for meningococcal culture (2)
• lumbar puncture
• this is mandatory in any patient in whom bacterial meningitis is suspected (3)
• this should be performed unless specifically contraindicated
• either cranial computed tomography (CT) or magnetic resonance imaging (MRI) is recommended as a precaution in selected patients before lumbar puncture to detect brain shift (3) (see note below)
• diagnosis of bacterial meningitis depends on CSF examination performed after lumbar puncture (4)
• CSF should be sent for:
• opening pressure
• gram stain, culture and sensitivity
• cell count
• biochemistry – glucose, protein, lactate
• meningococcal and pneumococcal PCR
• antibiotics should be given as a priority and should not be delayed because a lumbar puncture has not been performed.

In children and young people with suspected bacterial meningitis, perform a CRP and white blood cell count (5):

• if the CRP and/or white blood cell count is raised and there is a non specifically abnormal cerebrospinal fluid (CSF) (for example consistent with viral meningitis), treat as bacterial meningitis
• be aware that a normal CRP and white blood cell count does not rule out bacterial meningitis
• regardless of the CRP and white blood cell count, if no CSF is available for examination or if the CSF findings are uninterpretable, manage as if the diagnosis of meningitis is confirmed

If a child or young person has an unexplained petechial rash and fever (or history of fever), carry out the following investigations (5):

• full blood count
• C-reactive protein (CRP)
• coagulation screen
• blood culture
• whole-blood polymerase chain reaction (PCR) for N meningitidis
• blood glucose
• blood gas

Notes:

• indications for CT scan prior to lumbar puncture include (4):
• immunocompromised state (AIDS, immunosuppressive therapy, or after transplantation)
• history of CNS disease (mass lesion, stroke, or focal infection)
• new onset seizure
• papilloedema
• abnormal level of consciousness
• focal neurologic deficit

Reference:

• (1) Meningitis Research Foundation 2010. Lessons from research for doctors in training
• (2) McGill F et al. The UK joint specialist societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults. J Infect. 2016;72(4):405-38.
• (3) van de Beek D, et al. Community-Acquired Bacterial Meningitis in Adults. N Engl J Med 2006;354:44
• (4) Allan R. Tunkel, et al. Practice Guidelines for the Management of Bacterial Meningitis.Clinical Infectious Diseases (Infectious Diseases Society of America) 2004; 39:1267–84
• (5) NICE (June 2010). Bacterial meningitis and meningococcal septicaemia Management of bacterial meningitis and meningococcal septicaemia in children and young people younger than 16 years in primary and secondary care