Tests
1st tests to order
blood cultures
Test
Traditional definitive test for the diagnosis of meningococcemia and should be obtained from all people with suspected meningococcal infections. Positive blood cultures are reported in up to 86%, and positive cerebrospinal fluid cultures in up to 80%, of cases of clinically suspected meningococcal infection.[52][53]
To optimize sensitivity, appropriate volumes of blood should be obtained (at least 1-20 mL in children, 20 mL in adults).
Result
positive for Neisseria meningitidis
CBC and differential
Test
Patients with meningococcal infections may have an elevated WBC with a polymorphonuclear predominance. Patients with rapidly progressive infections, however, may initially have normal WBC. Neutropenia is not uncommon in severe infections. Thrombocytopenia and mild anemia are common.
Result
leukocytosis, anemia, thrombocytopenia
electrolytes, calcium, magnesium, phosphate, glucose
Test
Patients with severe meningococcal infections often have metabolic abnormalities, especially acidosis, hypokalemia, hypoglycemia, and hypocalcemia.
Result
acidosis, low Ca/Mg/PO₄, or hyper/hypoglycemia
coagulation profile (prothrombin time, INR, activated PTT, fibrinogen, fibrin degradation products)
Test
Coagulopathy is common in severe meningococcal infections.
Disseminated intravascular coagulation (DIC) is caused by acquired deficiencies of protein C, protein S, and antithrombin III; increases in plasminogen activator inhibitor and thrombin-activatable fibrinolysis inhibitor; and reduced activation of protein C on endothelial cells.
Result
evidence of DIC (prolonged thrombin time, elevated fibrin degradation products or D-dimer, low fibrinogen or antithrombin levels)
Tests to consider
cerebrospinal fluid (CSF) Gram stain
CSF cell count and differential
Test
In bacterial meningitis, CSF cell counts are typically >100 cells/microliter, with a polymorphonuclear predominance.
In fulminant infections and in young infants, CSF cell counts may be only mildly elevated or normal. In early bacterial meningitis, there may be a transient pleocytosis.[54]
Result
polymorphonuclear pleocytosis
CSF glucose, protein
Test
The majority of patients with bacterial meningitis have a CSF glucose concentration of <45 mg/dL or an absolute ratio of CSF to serum glucose concentrations of <0.4.[63] CSF protein is typically elevated. In rapidly progressive infections, values may be only slightly abnormal or normal.
Result
low glucose and elevated protein
CSF culture
Test
Neisseria meningitidis is isolated from up to 80% of people with clinically suspected meningococcal meningitis; therefore, a negative culture does not exclude infection.[52][53]
Treatment with antibiotics before cultures rapidly reduces the yield of testing, but administration of antibiotics should not be delayed if diagnostic evaluation cannot be completed promptly.
Result
N meningitidis
antigen detection in CSF
Test
Serogroup A, B, C, Y, and W-135 polysaccharide antigen can be detected by latex agglutination in 40% to 95% of patients with meningococcal meningitis.[50] Antigen may persist in CSF for several days, making this test useful in patients treated with antibiotics before diagnostic specimens have been obtained and for the rapid presumptive diagnosis of meningococcal infection.
Serogroup B Neisseria meningitidis and serotype K1 Escherichia coli polysaccharides cross-react, so test results should be interpreted cautiously in neonates.
Antigen detection testing on body fluids other than CSF, including serum or urine, is not recommended because of poor sensitivity and specificity.[50]
Result
N meningitidis capsular polysaccharide antigen
chest x-ray
Test
Diagnostic imaging should be obtained when meningococcal pneumonia or a focal hematogenous complication of meningococcemia is suspected. Chest x-rays in meningococcal pneumonia typically demonstrate lobar consolidation, with or without pleural effusion.
Result
may show lobar consolidation
CT head
Test
Commonly obtained prior to performing a lumbar puncture (LP) in patients with suspected bacterial meningitis to exclude the presence of a focal intracranial lesion. However, there is no conclusive evidence that an LP increases the risk of cerebral herniation in this setting.[61] Although head CT is also frequently performed to exclude significantly elevated intracranial pressure, it is not a sensitive test for this purpose.[62] Most authorities feel that pre-LP head CT is indicated in patients with significant alterations of mental status, focal abnormalities on neurologic exam, papilledema, antecedent focal central nervous system disease, or immunocompromise.[54][61]
If head CT is requested prior to an LP, antibiotics should be given immediately and not be delayed pending test results.
Result
normal; elevated intracranial pressure or intracranial lesion if other pathologies
Gram stain of non-CSF body fluid
Test
A Gram stain of pleural, pericardial, or joint fluid or material from a skin lesion aspirate or biopsy demonstrating gram-negative diplococci is suggestive of meningococcal infection in people with a compatible clinical illness, and may provide a rapid presumptive diagnosis.
Result
gram-negative diplococci
culture of non-CSF body fluid
Test
Positive culture of a normally sterile body fluid is indicative of focal meningococcal infections such as septic arthritis, pericarditis, endophthalmitis, peritonitis, and salpingitis. The sensitivity of cultures obtained from these sites is not well described.
Because Neisseria meningitidis is part of the normal flora of the nasopharynx, its isolation from this site does not confirm an illness is due to this organism.
Result
N meningitidis
immunohistochemical staining of skin lesion biopsy
Test
Biopsies of skin lesions in meningococcemia typically demonstrate hemorrhagic vasculitis with a polymorphonuclear infiltrate. Gram-negative diplococci may be visible within vessel walls or in thrombosed vessels. Immunostaining of Neisseria meningitidis antigens in tissue specimens increases test sensitivity and specificity.
Result
positive for N meningitidis
echocardiography
Test
In purulent pericarditis, echocardiography demonstrates pericardial effusion, with or without cardiac tamponade.
Result
possible pericardial effusion
joint x-ray
Test
In septic arthritis, radiographs may show typical findings.
Result
may show joint space widening or soft-tissue swelling
polymerase chain reaction
Test
Polymerase chain reaction (PCR) amplification of Neisseria meningitidis DNA from blood and CSF is more sensitive and specific than traditional microbiologic techniques.
PCR may be helpful in diagnosing bacterial meningitis in patients who have been pretreated with antibiotics.[55][56]
Real-time PCR assay can identify specific serogroups of N meningitidis from clinical isolates (typically blood or CSF).[57]
Multiplex PCR (such as the QIAstat-Dx Meningitis/Encephalitis [ME] Panel or the BioFire FilmArray ME Panel) is used to rapidly screen for multiple causative pathogens in a single reaction.[58][59][60]
Result
N meningitidis DNA
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