The levels of evidence (class I-IV) supporting the recommendations and ratings of recommendations (A-C, good practice point) are defined at the end of the "Major Recommendations" field.
Cerebrospinal fluid (CSF) should be immediately (i.e. <1 h) analysed after collection. If storage is required for later investigation this can be done at 4–8 degrees C (short term) or at –20 degrees C (long term). Only protein components and ribonucleic acid (RNA) (after appropriate preparation) can be analysed from stored CSF (good practice point).
The level B recommendation regarding CSF partitioning and storage states that 12 mL of CSF should be partitioned into three to four sterile tubes. It is important that the CSF is not allowed to sediment before partitioning. Store 3–4 mL at 4 degrees C for general investigations, cultivation and microscopic investigation of bacteria and fungi, antibody testing, polymerase chain reaction (PCR) and antigen detection. Bigger volumes (10–15 mL) are necessary for certain pathogens like Mycobacterium tuberculosis, fungi or parasites.
Normal CSF protein concentration should be related to the patient's age (higher in the neonate period and after age of 60 years) and the site of CSF collection (level B recommendation). Exact upper normal limits of protein concentration differ according to technique and examining laboratory.
The CSF to serum albumin concentration quotient (Qalb) should be preferred to total protein concentrations, partly because reference levels are more clearly defined and partly because it is not confounded by changes in other CSF proteins (level B recommendation).
The glucose concentration in CSF should be related to the blood concentration. Therefore, CSF glucose/serum ratio is preferable. Pathological changes in this ratio or in lactate concentration support bacterial or fungal meningitis or leptomeningeal metastases (level B recommendation).
Intrathecal immunoglobulin G (IgG) synthesis can be measured by various quantitative methods, but at least for the diagnosis of multiple sclerosis the detection of oligoclonal bands by appropriate methods is superior to any existing formula (level A recommendation). Patients with other diseases associated with intrathecal inflammation (e.g. patients with central nervous system (CNS) infections, may also have intrathecal IgA and IgM synthesis as assessed by non-linear formulae [Reiber hyperbolic formulae or extended indices], which should be preferred to the linear IgA and IgM indices) (level B recommendation).
Cellular morphology (cytological staining) should be evaluated whenever pleocytosis is found or leptomeningeal metastases or pathological bleeding is suspected (level B recommendation). If cytology is inconclusive in case of query CSF bleeding, measurement of bilirubin is recommended for up to 2 weeks after the clinical event.
For standard microbiological examination sedimentation at 3000 x g for 10 min is recommended (level B recommendation). Microscopy should be performed using Gram or methylene blue, Auramin O or Ziehl-Nielsen (Mycobacterium tuberculosis), or Indian ink stain (Cryptococcus). Depending on clinical presentation incubation with bacterial and fungal culture media can be useful. Anaerobic culture media are only recommended if there is suspicion of brain abscess. A viral culture is generally not recommended. A list of infectious agents and their association with different diseases as well as the recommended method of detection is provided in Table 4 of the original guideline document. The results of bacterial antigen detection have to be interpreted with respect to the microscopical CSF investigation and culture results. It is not routinely recommended in cases of negative microscopy. A diagnosis of bacterial nervous system infection based on antigen detection alone is not recommended (risk of contamination).
Definitions:
Evidence Classification Scheme for a Diagnostic Measure:
Class I: A prospective study in a broad spectrum of persons with the suspected condition, using a "gold standard" for case definition, where the test is applied in a blinded evaluation, and enabling the assessment of appropriate tests of diagnostic accuracy
Class II: A prospective study of a narrow spectrum of persons with the suspected condition, or a well-designed retrospective study of a broad spectrum of persons with an established condition (by "gold standard") compared to a broad spectrum of controls, where test is applied in a blinded evaluation, and enabling the assessment of appropriate tests of diagnostic accuracy
Class III: Evidence provided by a retrospective study where either persons with the established condition or controls are of a narrow spectrum, and where test is applied in a blinded evaluation
Class IV: Any design where test is not applied in blinded evaluation OR evidence provided by expert opinion alone or in descriptive case series (without controls)
Rating of Recommendations
Level A rating (established as useful/predictive or not useful/predictive) requires at least one convincing class I study or at least two consistent, convincing class II studies.
Level B rating (established as probably useful/predictive or not useful/predictive) requires at least one convincing class II study or overwhelming class III evidence.
Level C rating (established as possibly useful/predictive or not useful/predictive) requires at least two convincing class III studies.
Good practice point When only class IV evidence was available but consensus could be reached, the task force has offered advice as good practice points.
