Bacterial meningitis laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aysha Anwar, M.B.B.S[2]


Labortary findings of bacterial meningitis may include non specific and specific tests. Non specific findings include CBC, biochemical profile, coagulation profile and blood culture. Specific tests for bacterial meningitis include CSF analysis, CSF gram stain and culture.[1][2][3][4][5]

Lab findings

Labortary tests which may help identify the bacterial meningitis include non specific tests and specific diagnostic tests.

Non specific tests

Non specific tests include blood tests such as complete blood count, liver function tests, renal function tests, biochemistry, and coagulation profile.[1][2][3]

Laboratory findings
Test Findings
Complete blood count
White blood cell count
Blood culture
  • Positive in 50 to 90 percent of patients [1][2]
  • Two sets of blood cultures needed before antimicrobials

Specific tests

Specific diagnostic tests include lumbar puncture with CSF examination and CSF culture. CSF examination findings in bacterial meningitis are as follows:

Cerebrospinal fluid level Normal level Bacterial meningitis[9]
Cells/ul < 5 >300
Cells Lymphos:Monos 7:3 Gran. > Lymph
Total protein (mg/dl) 45-60 Typically 100-500
Glucose ratio (CSF/plasma)[10] > 0.5 < 0.3
Lactate (mmols/l)[11] < 2.1 > 2.1
Others ICP:6-12 (cm H2O) CSF gram stain, CSF culture, CSF bacterial antigen

CSF gram stain and culture:

CSF gram stain findings include the following:[4][5]

CSF Gram Stain Finding Causative Organism Culture medium Growth on culture medium
Gram positive diplococcus Streptococcus Pneumonia Blood agar plate Small, grey, moist (sometimes mucoidal), watery colonies

with green zone of allpha hemolysis

Gram negative diplococcus Neisseria Meningitides Blood agar plate and chocolate agar plate Round, smooth, moist, glistening, and convex
Gram positive coccobacillus Listeria Monocytogenes Brain heart infusion Isolated small 1mm colonies creamy white in colour and dome shaped
Small pleomorphic gram - negative coccobacilli Haemophilus Influenzae Chocolate agar plate enriched with NAD and hematin (X) Large, colorless-to-grey, opaque colonies


  1. 1.0 1.1 1.2 Geiseler PJ, Nelson KE, Levin S, Reddi KT, Moses VK (1980). "Community-acquired purulent meningitis: a review of 1,316 cases during the antibiotic era, 1954-1976". Rev Infect Dis. 2 (5): 725–45. PMID 6763303.
  2. 2.0 2.1 2.2 Talan DA, Hoffman JR, Yoshikawa TT, Overturf GD (1988). "Role of empiric parenteral antibiotics prior to lumbar puncture in suspected bacterial meningitis: state of the art". Rev Infect Dis. 10 (2): 365–76. PMID 3287565.
  3. 3.0 3.1 Kanegaye JT, Soliemanzadeh P, Bradley JS (2001). "Lumbar puncture in pediatric bacterial meningitis: defining the time interval for recovery of cerebrospinal fluid pathogens after parenteral antibiotic pretreatment". Pediatrics. 108 (5): 1169–74. PMID 11694698.
  4. 4.0 4.1 Accessed on Jan 12, 2017
  5. 5.0 5.1 Jones GS, D'Orazio SE (2013). "Listeria monocytogenes: cultivation and laboratory maintenance". Curr Protoc Microbiol. 31: 9B.2.1-7. doi:10.1002/9780471729259.mc09b02s31. PMC 3920655. PMID 24510292.
  6. 6.0 6.1 Kaplan SL (1999). "Clinical presentations, diagnosis, and prognostic factors of bacterial meningitis". Infect Dis Clin North Am. 13 (3): 579–94, vi–vii. PMID 10470556.
  7. Demissie DE, Kaplan SL, Romero JR, Leake JA, Barson WJ, Halasa NB; et al. (2013). "Altered neutrophil counts at diagnosis of invasive meningococcal infection in children". Pediatr Infect Dis J. 32 (10): 1070–2. doi:10.1097/INF.0b013e31829e31f1. PMID 23736141.
  8. Brouwer MC, van de Beek D, Heckenberg SG, Spanjaard L, de Gans J (2007). "Hyponatraemia in adults with community-acquired bacterial meningitis". QJM. 100 (1): 37–40. doi:10.1093/qjmed/hcl131. PMID 17178734.
  9. Negrini B, Kelleher KJ, Wald ER (2000). "Cerebrospinal fluid findings in aseptic versus bacterial meningitis". Pediatrics. 105 (2): 316–9. PMID 10654948.
  10. Chow E, Troy SB (2014). "The differential diagnosis of hypoglycorrhachia in adult patients". Am J Med Sci. 348 (3): 186–90. doi:10.1097/MAJ.0000000000000217. PMC 4065645. PMID 24326618.
  11. Leen WG, Willemsen MA, Wevers RA, Verbeek MM (2012). "Cerebrospinal fluid glucose and lactate: age-specific reference values and implications for clinical practice". PLoS One. 7 (8): e42745. doi:10.1371/journal.pone.0042745. PMC 3412827. PMID 22880096.

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