Diagnosis and Management of Meningitis

Blood Samples Required

Blood cultures should be obtained prior to antibiotic administration whenever possible, or within the first hour of hospital arrival if antibiotics were given in the community, as recommended by the Infectious Diseases Society of America 1, 2
Pneumococcal and meningococcal PCR (EDTA sample) can identify causative organisms even after antibiotics have been started, with a high degree of accuracy 1
Blood glucose measurement is essential to compare with CSF glucose, helping to differentiate between bacterial and viral meningitis 1
Lactate measurement can provide valuable information on the severity of the infection 1
Procalcitonin measurement can help differentiate bacterial from viral meningitis, with a high degree of sensitivity and specificity 1, 2
Full blood count, urea, creatinine, electrolytes, liver function tests, and clotting screen can provide important information on the patient's overall condition 1
Storage sample for potential serological testing if a cause is not identified, with a convalescent sample 4-6 weeks later, can help identify the causative organism 1

CSF opening pressure measurement is essential, unless lumbar puncture is performed in sitting position, to assess for increased intracranial pressure 1
CSF glucose with concurrent plasma glucose can help diagnose bacterial meningitis, with a low CSF:blood glucose ratio suggesting bacterial infection 1, 3
CSF protein measurement can help differentiate between bacterial and viral meningitis, with elevated levels suggesting bacterial infection 1, 3
CSF cell count and white cell differential can provide valuable information on the type of infection, with polymorphonuclear predominance suggesting bacterial infection and lymphocytic predominance suggesting viral infection 3
CSF Gram stain can provide rapid diagnosis in 70-85% of bacterial meningitis cases, with a high degree of accuracy 4
CSF culture is the gold standard for bacterial identification, providing definitive diagnosis 4
CSF PCR for common pathogens, including enterovirus, HSV-1, HSV-2, and VZV, can provide rapid diagnosis with high sensitivity and specificity 5

Nasopharyngeal swabs for meningococcal isolation can provide valuable information on the causative organism, especially if the patient has received antibiotics 4
Stool and/or throat swabs for enterovirus PCR can help diagnose viral meningitis, with a high degree of accuracy 5

If lumbar puncture is delayed due to contraindications, blood samples should be collected and antibiotics administered before neuroimaging, as recommended by the Infectious Diseases Society of America 2, 6
Use of smaller gauge needles (22G practical minimum) and atraumatic needles can reduce post-LP headache risk, with a significant reduction in complications 1
Replacement of the stylet before needle withdrawal may reduce post-LP headache risk, with a significant reduction in complications 1

Delay in obtaining samples should never postpone antibiotic administration in suspected bacterial meningitis, as this increases mortality, emphasizing the importance of prompt treatment 2, 6
CSF findings may be altered by prior antibiotic administration, but will likely still provide evidence for or against bacterial meningitis, highlighting the need for careful interpretation of results 3
Lumbar puncture is contraindicated in patients with signs of increased intracranial pressure, until pressure is controlled, emphasizing the importance of careful patient selection 6