Cerebrospinal Fluid Analysis: Reference Range, Interpretation, Collection and Panels (2024)

Conditions associated with an abnormal CSF analysis include (but are not limited to) the following:

• Infectious diseases (eg, encephalitis, meningitis)

• Intracranial/subarachnoid hemorrhage

• Inflammatory or autoimmune diseases (eg, multiple sclerosis, Guillain-Barre syndrome, meningeal sarcoidosis)

• Primary or metastatic central nervous system (CNS) malignancies

Conditions associated with changes in the appearance of CSF

Under normal circ*mstances, CSF samples are clear and colorless, appearing similar to water.

Xanthochromia is the term used for any kind of discoloration of CSF.Multiple conditions are associated with xanthochromia, including the following ^{[2, 3, 5]} :

• Traumatic tap

• Presence of carotene, melanoma

• increased bilirubin concentration - Due to liver diseases, hemolytic diseases (also increased free hemoglobin concentration), inborn errors of metabolism (kernicterus), and the significantly delayed bilirubin clearance that can occur in premature babies; the bilirubin concentration will also be elevated in serum, and patients are often jaundiced

Specific CSF discolorations include the following:

• Infectious meningitis - Turbid, milky, cloudy CSF samples

• Hemorrhage (subarachnoid hemorrhage) or traumatic tap - Pink to orange CSF samples, depending on the concentration of free hemoglobin

• Kernicterus - Dark yellow or orange CSF samples with increased bilirubin

• Meningeal melanosarcoma - Dark CSF samples with increased melanin

• Disorders affecting the blood-brain barrier and demyelinating conditions - Cloudy CSF samples with increased proteins (above 150 mg/dL), such as albumin and immunoglobulin G (IgG)

• Increased carotene - Orange discoloration of CSF samples

If CSF samples are centrifuged immediately, xanthochromia due to traumatic tap should not occur. However, if CSF samples are carefully centrifuged immediately and the supernatant is still xanthochromic, this indicates that bleeding may have occurred 2-4 hours before sample collection. Furthermore, in about 10% of patients with subarachnoid hemorrhage, the CSF samples might be clear if the samples are collected 12 hours after the hemorrhage occurred.

Typically, high levels of oxyhemoglobin occur in CSF fluid obtained through a traumatic lumbar puncture, in which red blood cells (RBCs) enter the subarachnoid space via direct needle puncture. This interferes with the ability to determine whether xanthochromia, and thus subarachnoid hemorrhage, is present. However, a retrospective study by China et al found that when a repeat lumbar puncture was performed on patients after the initial, traumatic one, it was possible to determine that xanthochromia was absent, thereby ruling out the possibility of subarachnoid hemorrhage. According to the study, the timing of the second puncture must be determined on a case-by-case basis, with repeat punctures in the report being performed an average of 2.4 days after the traumatic puncture. The investigators stated that performing the repeat lumbar puncture too soon (eg, less than 12 hours) after the first could still produce equivocal results, while performing the second puncture too long after the initial one could put the patient at greater risk for morbidity and mortality, due to a missed diagnosis. ^[6]

Bilirubin evaluation in CSF (and serum) is the most effective biomarker to be considered for evaluation of potential subarachnoid hemorrhage. However, a traumatic tap concurrent with subarachnoid hemorrhage can be confusing to interpret.

Atraumatic tap introduces red cells into the CSF, but this contamination clears as the collection proceeds from tubes 1 to 4.In a traumatic tap, bilirubin is not produced, given that bilirubin production is an in vivo process. Spectrophotometric evaluation of CSF can provide additional information regarding the presence of oxyhemoglobin due to traumatic tapping (absorbancepeak at 415 nm) and the presence of bilirubin due to subarachnoid hemorrhage (absorbancepeak at 476 nm). ^[7] However, large oxyhemoglobin peaks may obscure the region where bilirubin absorbance is normally measured and render interpretation difficult. A series of interpretative comments is suggested in guidelines from the United Kingdom. ^[8]

Oily CSF samples are associated with the presence of radiographic contrast media.

Conditions associated with changes in the biochemical composition of CSF

There are a few common analytes that are routinely evaluated in CSF: glucose, lactate, glutamine, total proteins, albumin, IgG, and bilirubin.

Changes in glucose concentration

Conditions associated with changes in the glucose concentration of CSF include the following:

• Bacterial, fungal, and tuberculous meningitis (but not viral)

• Primary or metastatic meningeal malignancy

• Subarachnoid hemorrhage

• Hypoglycemia

  See Also

  Avera: Total Protein and A/G RatioStillwater Medical | Total Protein and A/G RatioPOS1513-HPR THE USE OF SUPRAMAXIMAL VERIFICATION TESTING FOR DETERMINING A ‘TRUE’ MAXIMAL EFFORT DURING CARDIOPULMONARY EXERCISE TESTING IN PEOPLE WITH RHEUMATOID ARTHRITIS AND PHYSICALLY INACTIVE NON-RA CONTROLSUrine Protein-Creatinine Ratio Test: What It Measures, Levels

The normal concentration of glucose in CSF samples is 45-80 mg/dL or 60-80% of that in the plasma (for glucose plasma concentrations less than 400 mg/dL).

Absolute decreased CSF glucose level and especially decreased CSF glucose level in relation with serum are usually associated with bacterial or fungal meningitis. However, in patient with a normal CSF glucose concentration but with increased number of WBC, viral meningitis should be suspected. For accurate interpretation of CSF glucose concentration, serum glucose should be evaluated in serum samples collected about 2 hours prior to spinal tapping (allow time for equilibrium) and all specimens (CSF and serum) should be tested immediately to avoid glycolysis. ^{[2, 3]}

Laboratory testing methods employ hexokinase (reference method) or glucose oxidase. A patient's serum and CSF samples must both be tested using the same method/instrument for accurate interpretation of results. Glucometers and point-of-care testing (POCT) methods/instruments cannot be used for glucose testing in CSF samples.

Elevation of CSF lactate

Conditions associated with elevated CSF lactateinclude any condition related to decreased blood flow or hypoxia (eg, head trauma), such as the following:

• Intracranial hemorrhage

• Cerebral arteriosclerosis

• Hypotension

• Metastatic cancer

• Trauma

• Seizures

• Bacterial meningitis

• Mycoplasma meningitis

Evaluation of lactic acid concentration in CSF is useful for the diagnosis and management of different types of meningitis. Generally, the following guidelines can be applied:

• CSF lactate >35 mg/dL is seen in patients with bacterial meningitis

• CSF lactate 25-35 mg/dL is seen in patients with tubercular and fungal meningitis

• CSF lactate < 25 mg/dL is seen in patients with viral meningitis

Lactate dehydrogenase (LDH) can be used as a surrogate for lactate, but the assay has more limitations, including more analytic variability and interference from contamination with RBCs. RBCs contain high concentrations of lactate and LDH, so xanthochromic CSF samples with elevated hemoglobin and/or RBCs can lead to falsely elevated lactate and LDH results. ^[3]

Conditions associated with elevated CSF lactate/LDHinclude the following:

• Intracranial hemorrhage

• Bacterial meningitis

Elevation of CSF glutamine

Glutamine results from the amination of a-ketoglutarate with ammonia and it represents the main way in which the toxic metabolite ammonia is removed from the CNS. In the conditions in which ammonia accumulates, such as in liver disease, inherited urea cycle disorders, or Reye syndrome, glutamine concentration will raise as well. The normal glutamine concentration in CSF is 8-18 mg/dL. Increased concentration of glutamine in CSF is followed rapidly by signed and symptoms, while at concentration of 35 mg/dL or above, strong seizures and coma can occur. Evaluation of glutamine in CSF is a common practice in the case of patients, especially children, with coma of unknown origin. ^[2]

Conditions associated with cerebrospinal protein variation

The protein concentration in CSF varies with age and level of tapping (eg, lumbar, ventricular). It correlates well with the concentration of total proteins and different fractions in serum, but they are significantly lower. The predominant fraction in CSF is albumin, similarly as in serum. Decreased total protein concentration in CSF is generally associated with CSF leakage, while elevation of proteins in CSF can be seen in a multitude of conditions.

In addition to medical conditions, protein concentration can be falsely elevated in CSF due to traumatic tap and increased RBC and hemoglobin. Therefore, corrections are commonly applied: if CSF sample is xanthochromic, for every 10³ RBC counted, 1.1 mg/dL should be subtracted from the measured total protein concentration of CSF. ^{[2, 3]}

CSF protein fractions and CSF IgG

In certain conditions, such as in multiple sclerosis, evaluation of total proteins in CSF is not sufficient. Evaluation of different protein fractions and various immunoglobulins is necessary.

IgG immunoglobulins can be produced by the plasma cells on both sides of the blood-brain barrier: within CNS and in serum. When IgG fraction of CSF is elevated, the immediate question targets the integrity of the blood-brain barrier. Therefore, evaluations of serum albumin and serum IgG and normalization of IgG concentration of CSF, taking into account these serum concentrations, are necessary. ^{[2, 3, 9]}

Quotient of albumin

Albumin is synthetized in the liver and can reach CSF via diffusion. Normal albumin concentration in CSF is about 500 times lower than that of serum. Abnormal concentration of albumin in CSF is most often associated with disruption in the blood-brain barrier (eg, trauma, inflammation). Quotient of albumin (Q_alb) is a calculated parameter that normalizes the CSF concentration of albumin to the concentration of albumin in serum:

Q-Alb=(Alb_CSF/Alb_Serum) X 1000

Normally, the Quotient of albumin is less than 9 and reflects intact blood-brain barrier. However, the higher the quotient of albumin, the higher the blood-brain barrier damage and vice-versa. ^{[2, 3, 9]}

IgG Index

IgG index is a calculated parameter that normalizes the IgG concentration in CSF, taking into account the concentration of albumin (Q_alb) and IgG in serum:

IgG index = (IgG_CSF/IgG_Serum) / Q-Alb

IgG index provides a better idea regarding IgG molecules entering CSF via damaged blood-brain barrier. Variations exist between laboratories regarding the normal value of IgG index (generally 0.25-0.7). However, generally if IgG index is greater than 0.7, the patient is actively producing IgG within CSF, while the blood-brain barrier is intact. A decreased IgG index reflects damaged blood-brain barrier, which allows IgG crossing (eg, stroke, tumors, some meningitis). ^{[2, 3, 9]}

CSF isoelectric focusing electrophoresis (IEF) and testing for multiple sclerosis: oligoclonal banding

The CSF oligoclonal bands represent a population of gamma-migrating globulins with similar electrophoretic mobility. IEF is significantly more sensitive for optimal separation of CSF oligoclonal bands than the regular CSF protein electrophoresis.

Detection of oligoclonal bands is associated with multiple neurological conditions. Up to 90% of patients with multiple sclerosis present oligoclonal band upon CSF IEF evaluation, while the blood-brain barrier is intact (normal Qalb) and IgG index can be within normal range. ^{[2, 3, 9]}

For correct interpretation of CSF IEFresults, serum IEF should be run in parallel. Few patterns/clinical situations can be encountered:

Although detection of oligoclonal bands is most often associated with multiple sclerosis, other causes of oligoclonal banding should be excluded. Multiple myeloma and other monoclonal gammopathies, as well as some viral infections, are characterized by the presence of immunoglobulin banding in serum. Upon disruption of the blood-brain barrier or after introduction of blood into the CSF samples during a traumatic tapping, banding can be detected in a matching pattern in both CSF and serum. Integrity of the blood-brain barrier should be always evaluated (eg, Qalb). Therefore, for correct interpretation of CSF IEF results, serum immunofixation should be considered for all positive cases with matching pattern. In addition, some neurological disorders, such as encephalitis, neurosyphilis, some forms of meningitis and Guillain-Barre syndrome can also produce CSF-specific banding. Clinical correlations should always be considered. Oligoclonal banding will remain positive during multiple sclerosis remission, but it will disappear in other disorders. ^{[2, 3, 9]}

CSF-specific transferrin and evaluation of CSF leakage

Transferrin is present in serum, in normal circ*mstances, only as a sialated isoform. However, CSF contains the specific, desialated isoform, also known as tau protein or tau transferrin. Normal serum transferrin (sialated isoform) migrates upon electrophoresis anodically and make up most of the beta-1 electrophoretic band. However, the CSF-specific desialated isoform (tau transferrin) is more positive and, therefore, it migrates more cathodically, as a distinct band, designated as “beta-2 transferrin.” Note that this is a CSF-specific band/isoform and it is not detected in serum in normal circ*mstances. These electrophoretic properties of transferrin isoforms have diagnostic application in rhinorrhea or otorrhea (leakage of CSF into the nose or ear canal, usually as a result of head trauma, tumor, congenital malformation, or surgery). Beta-2 transferrin is used as an endogenous marker for CSF leakage.

Upon electrophoresis of ear or nose fluid samples, common transferrin migrates in the beta-1 electrophoretic fraction (“beta-1 transferrin”), while beta-2 transferrin, which is the CSF-specific variant of transferrin, if present in the ear or nose fluid samples, will migrate as an additional distinctive band. Detection of beta-2 transferrin in ear or nose fluid samples is an indication of CSF leakage. ^[9]

Summary of chemistry evaluation of CSF in different clinical conditions

Chemistry evaluation of CSF in different clinical conditions is summarized below. ^[2] Serologic testing may be necessary to establish the final diagnosis.

Table. Changes in Analytes With Various CNS Disease (Open Table in a new window)

Conditions associated with changes in microscopic/cellular findings inCSF

Conditions associated with a reactive CSF lymphocytosis include the following:

• Meningitis

• Syphilitic meningoencephalitis

• Parasitic CNS infection

• Multiple sclerosis

• Guillain-Barré syndrome

• Meningeal sarcoidosis

• Polyneuritis

• Subacute sclerosing panencephalopathy (SSPE)

Conditions associated with CSF monocytosis include the following:

• Chronic or treated bacterial meningitis

• Syphilitic, viral, fungal, amebic meningitis

• Intracranial hemorrhage

• Cerebral infarct

• CNS malignancy

• Foreign body reaction

Conditions associated with increased CSF polymorphonuclear neutrophils include the following:

• Bacterial meningitis

• Acute viral meningitis

• Tuberculous and fungal meningitis

• Amebic encephalomyelitis

• Brain abscess

• Subdural empyema

• CNS hemorrhage

• Cerebral infarct

• Malignancies

• Previous lumbar puncture

• Intrathecal chemotherapy

• Seizure

Biomarkers for neurodegenerative diseases and dementia

A few blood biomarkers have been evaluated in serum and CSF samples to be used for assessments of neurodegenerative diseases and dementia, with promising results. These include the following:

• Amyloid beta protein

• Myelin basic protein (MBP) and myelin-associated glycoprotein (MAG) antibodies

• Neuron-specific enolase