- CSF Microbiology
- Microbiology, CSF
- C+S (CSF)
- Culture & Sensitivity (CSF)
- 1-3 mL of Cerebrospinal Fluid (CSF) is collected into each sterile plastic tube; typically 4 tubes are collected
- CSF is collected by lumbar puncture ("spinal tap") using sterile technique
Typical use of each tube:
- Tube 1 - For chemistry and serology testing
- Tube 2 - For microbiology
- Tube 3 or 4 - For miscellaneous testing
- Tube 3 or 4 – For cell count
Overview of CSF
- Cerebrospinal Fluid (CSF) is a clear fluid formed in the brain that "bathes" the brain and fills the subarachnoid space.
- CSF is in contact with the extracellular fluid of the brain and its composition is reflective of the brain itself.
- CSF mainly helps in regulation of intracranial pressure (ICP), supply of nutrients to the nervous tissues, and removal of waste products.
- CSF protects the brain and the spinal cord from injury.
- Despite CT and MRI, CSF analysis remains a critical diagnostic tool in the evaluation of neurological disorders.
CSF Microbiology
CSF examination for microbes primarily includes bacteria, fungi, viruses, tuberculosis, amoeba and parasites. Bacterial and viral infections are most common. Certain at risk populations may be predisposed to parasitic or fungal CNS infections.
Table of CSF findings with infection
| Type of infection | WBCs/mm3 | WBC Differential | Protein | Glucose Ratio (Serum:CSF) | Lactate | Opening Pressure |
|---|---|---|---|---|---|---|
| Bacterial | >100 (usually  1000) | Neutrophils dominate in most cases. Lymphocytosis in 10% of cases | Elevated | Normal or decreased | Elevated | Elevated |
| Viral |  300 | Lymphocytosis typical; Neutrophils may dominate early in course | Normal or elevated | Normal (may be decreased in mumps or LCM) | Normal | Normal (typically) |
| Fungal or Tubercular | 500 | Lymphocytosis typical | Elevated | Decreased (typically) | Elevated | Variable |
CSF Formation/Circulation
- In an adult, approximately 150 mL of CSF is in circulation at any moment.
- 500-600 mL of CSF is formed and absorbed daily
- CSF is formed by the choroid plexus, primarily in the lateral ventricles (to a smaller degree in the 3rd and 4th ventricles)
- CSF circulates through the interventricular foramina to the third ventricle, through the cerebral aqueduct into the fourth ventricle and finally to the subarachnoid space covering the brain and spinal cord.
- Following circulation through the subarachnoid space, the CSF enters the intracranial sinuses to be resorbed by the arachnoid villi and granulations
Relationship of blood to CSF
- The blood brain barrier is relatively impervious to cellular compounds; however, CSF is an ultra-filtrate of serum and as such is impacted by the composition of serum
- The blood-CSF barrier is not as impervious and smaller molecular compounds such as glucose, albumin and immunoglobulins will find their way into the CSF from serum, via diffusion.
- A blood specimen drawn at a time close to obtaining CSF is useful for comparison
- CSF glucose level is usually 60% of that of blood glucose level
- CSF protein is typically only 20% derived from the brain and 80% from diffusion from serum into subarachnoid circulating CSF
This section covers CSF microbiology. Other sections provide detailed information on each other components of CSF testing.
General overview
- CSF is obtained to evaluate for infection, inflammation, malignancy, or bleeding in the central nervous system
- CSF examination for microbes primarily includes bacteria, fungi, viruses, tuberculosis, amoeba and parasites
- Although bacterial and viral infections are most common; certain at risk populations may be predisposed to parasitic or fungal CNS infections
- Additional special tests (mostly experimental) are increasingly available for the evaluation of other conditions such as multiple sclerosis or dementia
Information gained from Lumbar Puncture and CSF Analysis includes:
- Opening pressure (pressure in the brain)
- Glucose
- Protein
- Cell counts
- Gram stain
- Culture for bacteria, fungus, virus
- Bacterial antigens
- Fungal stains
- Viral testing
- Syphilis testing
- Lyme testing
- CSF immunoglobulin levels
- CSF angiotensin-converting enzyme (Neurosarcoid)
- Tumor markers
- Alpha-fetoprotein (AFP)
- Beta-glucuronidase
- Carcinoembryonic antigen (CEA)
- Human chorionic gonadotropin (HCG)
- Lysozyme (muramidase)
- Lactate in mitochondrial cytopathies
- Other specialized testing as condition dictates
Table of CSF findings with infection
| Type of infection | WBCs/mm3 | WBC Differential | Protein | Glucose Ratio (Serum:CSF) | Lactate | Opening Pressure |
|---|---|---|---|---|---|---|
| Bacterial | >100 (usually 1000) | Neutrophils dominate in most cases. Lymphocytosis in 10% of cases | Elevated | Normal or decreased | Elevated | Elevated |
| Viral | 300 | Lymphocytosis typical; Neutrophils may dominate early in course | Normal or elevated | Normal (may be decreased in mumps or LCM) | Normal | Normal (typically) |
| Fungal or Tubercular | 500 | Lymphocytosis typical | Elevated | Decreased (typically) | Elevated | Variable |
Contraindications to performing lumbar puncture:
- Infection overlying site of needle insertion
- Coagulation defects (most commonly increased PT)
- Increased intracranial pressure; especially with space occupying lesion present (e.g. tumor, abscess) as herniation of the brain is a theoretic risk
- Degenerative joint disease (relative contraindication)
Related laboratory tests include:
- Complete blood count
- Blood culture
- Lyme serology
- Syphilis serology (RPR, VDRL)
This section covers CSF microbiology. Other sections provide detailed information on each other components of CSF testing.
The normal result on CSF testing is that no organisms are present. A Gram Stain and Culture are always performed; however, more specialized testing may be required in certain cases. Other causes of CSF infection such as viral, fungal, tuberculosis, Lyme disease, or parasites, may not be diagnosed if the correct testing is not ordered.
Bacterial testing:
- Gram Stain: Negative (No bacteria seen)
- Culture: Negative (No Growth)
- Bacterial antigen testing*: Negative
- Listeria monocytogenes PCR: Negative
* Note that antigen testing is probably of no value over Gram's stain
Viral testing:
- Normal result is negative for all viruses.
- PCR testing is available for some viruses; whereas viral cultures and other advanced testing is required for some agents.
- Enteroviruses are the most common cause of viral meningitis in immunocompetent patients, whereas adenovirus is an important cause in immunosuppressed patients.
- Potential viral infections of the CSF include:
- Adenovirus
- Arboviruses (St. Louis encephalitis)
- Colorado tick fever virus
- Cytomegalovirus (CMV)
- Enterovirus (Coxsackievirus, echovirus)
- Epstein-Barr Virus (EBV)
- Equine encephalitis viruses
- Herpes simplex virus (HSV-1,HSV-2)
- HIV virus
- Human herpes 6 virus
- Lymphocytic choriomeningitis virus (LCMV)
- Measles virus
- Mumps virus
- Poliovirus
- Rabies virus
- Rubella virus
- Varicella Zoster Virus
- West nile virus
Fungal testing:
- India ink: Negative
- Culture: Negative (No Growth)
- Cryptococcal antigen testing: Negative
- Histoplasma antigen testing: Negative
Lyme testing:
- CSF Lyme PCR: Negative
- CSF B. burgdorferi IFA or ELISA: Negative
- CSF B. burgdorferi Western Blot Testing: Negative
Mycoplasma testing:
- Serum cold agglutinins: Normal is <1:16
Parasitic testing:
- Microscopic examination of CSF: No amoeba
- Cystercercosis titer (Blood & CSF): Negative
- Toxoplasmosis PCR testing: Negative
- Cystercercosis, Toxoplasmosis of the brain usually diagnosed on CT brain rather than CSF specimen
Syphilis testing:
- Dark field microscopy: Negative
- VDRL: Non-reactive
- RPR: Negative
- FTA-Abs: Negative
Tuberculosis testing:
- Mycobacterium tuberculosis culture (AFB culture): Negative (often takes 6 weeks)
- AFB Smear: Negative
- PCR testing: Negative
This section covers CSF microbiology. Other sections provide detailed information on each other components of CSF testing.
A high (positive) result is abnormal on any of the items listed below; as CSF should be sterile and uninfected.
It is important to note that if the right test isn't ordered, the diagnosis will not be made. Gram stain and bacterial culture have excellent yield for diagnosis of bacterial meningitis; however, different testing may be required for other causes of CSF infection.
Bacterial testing:
- Gram Stain: Positive
- Culture: Positive
- Bacterial antigen testing*: Positive
- Listeria monocytogenes PCR: Positive
* Note that antigen testing is probably of no value over Gram's stain
Organisms found may include:
- Streptococcus pneumonia
- Streptococcus agalactiae (Group B Streptococcus)
- Neisseria meningitides
- Listeria monocytogenes
- Haemophilus influenzae type B (HIB)
- Escherichia coli
- Aerobic gram-negative rods
- Staphylococcus aureus
- Pseudomonas
- Group A Streptococcus
Viral testing:
- Positive result would be virus identified in CSF.
- PCR testing is available for some viruses; whereas viral cultures and other advanced testing is required for some agents.
- Enteroviruses are the most common cause of viral meningitis in immunocompetent patients, whereas adenovirus is an important cause in immunosuppressed patients.
- Potential viral infections of the CSF include:
- Adenovirus
- Arboviruses (St. Louis encephalitis)
- Colorado tick fever virus
- Cytomegalovirus (CMV)
- Enterovirus (Coxsackievirus, echovirus)
- Epstein-Barr Virus (EBV)
- Equine encephalitis viruses
- Herpes simplex virus (HSV-1, HSV-2)
- HIV virus
- Human herpes 6 virus
- Lymphocytic choriomeningitis virus (LCMV)
- Measles virus
- Mumps virus
- Poliovirus
- Rabies virus
- Rubella virus
- Varicella Zoster Virus
- West nile virus
Fungal testing:
- India ink: Positive
- Culture: Growth present
- Cryptococcal antigen testing: Positive
- Histoplasma antigen testing: Positive
Lyme testing:
- CSF Lyme PCR: Positive
- CSF B. burgdorferi IFA or ELISA: Positive
- CSF B. burgdorferi Western Blot Testing: Positive
Mycoplasma testing
- Serum cold agglutinins: >1:16
* Note: In Mycoplasma meningoencephalitis titers are typically >1:1,000
Parasitic testing:
- Microscopic examination of CSF: Amoeba identified
- Cystercercosis titer (Blood & CSF): Positive
- Toxoplasmosis PCR testing: Positive
- Cystercercosis, Toxoplasmosis of the brain usually diagnosed on CT brain rather than CSF specimen
Syphilis testing:
- Dark field microscopy: Positive
- VDRL: Reactive
- RPR: Positive
- FTA-Abs: Positive
Tuberculosis testing:
- Mycobacterium tuberculosis culture (AFB culture): Positive (often takes 6 weeks)
- AFB Smear: Positive
- PCR testing: Positive
This section covers CSF microbiology. Other sections provide detailed information on each other components of CSF testing.
N/A as there are no significant conditions associated with a low (Negative) result.
This section covers CSF microbiology. Other sections provide detailed information on each other components of CSF testing.
- Bera S et al. Detection of antigen and antibody in childhood tuberculous meningitis. Indian J Pediatr. 2006 Aug; 73(8):675-9
- Chavanet P et al. Performance of a predictive rule to distinguish bacterial and viral meningitis. J Infect. 2006 Aug 1; [Epub ahead of print]
- Freedman MS et al. Recommended standard of cerebrospinal fluid analysis in the diagnosis of multiple sclerosis: a consensus statement. Arch Neurol. 2005 Jun;62(6):867-70
- Garnier JM et al. Extrapulmonary infections due to Mycoplasma pneumoniae. Arch Pediatr. 2005 Apr; 12 Suppl 1:S2-6.
- Griffiths PD et al. Malformations of the fetal spine using in utero MR imaging. Cerebrospinal Fluid Research 2005, 2(Suppl 1): S18 doi: 10.1186/1743-8454-2-S1-S18
- Jakka SR et al. Characteristic abnormalities in cerebrospinal fluid biochemistry in children with cerebral malaria compared to viral encephalitis. Cerebrospinal Fluid Research 2006, 3:8 doi: 10.1186/1743-8454-3-8
- Jaton K et al. Development of polymerase chain reaction assays for detection of Listeria monocytogenes in clinical cerebrospinal fluid samples. J Clin Microbiol. 1992 Aug; 30(8): 1931-6.
- Kawashima H et al. Primary biomarkers in cerebral spinal fluid obtained from patients with influenza-associated encephalopathy analyzed by metabolomics. Int j Neurosci. 2006 Aug; 116(8): 927-36
- Mein J et al. CSF bacterial antigen detection tests offer no advantage over Gram's stain in the diagnosis of bacterial meningitis. Pathology. 1999 Feb; 31(1):67-9.
- Narkeviciucte I et al. Aetiological diagnostics of acute bacterial meningitis in children. Scand J Infect Dis. 2006; 38(9): 782-7
- Rikonen R et al. Cerebrospinal fluid insulin-like growth factors IGF-1 and IGF-2 in infantile autism. Dev Med Child Neurol. 2006 Sep; 48(9): 751-5
- Seehusen DA et al. Cerebrospinal Fluid Analysis. Am Fam Phy. 2003;68:1103-8.
- Silverberg G et al. Elevated cerebrospinal fluid pressure in patients with Alzheimer's disease. Cerebrospinal Fluid Research 2006, 3:7 doi: 10.1186/1743-8454-3-7
- Vidal JE et al. PCR Assay Using Cerebrospinal Fluid for Diagnosis of Cerebral Toxoplasmosis in Brazilian AIDS patients. J Clin Microbiol. 2004; 42(10): 4765-4768.