Biochemistry analysis in cerebrospinal fluid

  • Glucose
  • Chloride
  • Glutamine
  • Lactate
  • Lactate dehydrogenase (LD/LDH) in cerebrospinal fluid
  • Total protein in cerebrospinal fluid
  • Globulins in cerebrospinal fluid
  • CSF protein electrophoresis
  • Albumin in cerebrospinal fluid
  • IgG immunoglobulin in cerebrospinal fluid
  • Blood-brain barrier
  • VDRL test for syphilis

 

Glucose

The CSF glucose level varies with the blood glucose levels. CSF glucose is usually 60% to 70% of the blood glucose. The blood glucose specimen should be obtained at least 30 to 60 minutes before lumbar puncture for comparison. Any changes in blood glucose are reflected in the CSF after 1 to 3 hours. This measurement is helpful in determining impaired transport of glucose from plasma to CSF and increased utilization of glucose by the CNS, leukocytes, and microorganisms.

Chloride

Any condition that alters the blood plasma chloride level will also affect the CSF level. Chlorides in CSF are higher (1.2-1) than in blood plasma. The measurement of CSF chloride is most useful in the diagnosis of tuberculous meningitis.

Glutamine

Glutamine (GLN) is synthesized in brain tissue from ammonia and glutamic acid. The production of glutamine provides a mechanism for removing ammonia from the CNS.
This measurement is used for determination of hepatic encephalopathy and CSF acidosis.

Lactate

The source of lactic acid in the cerebrospinal fluid probably is the CNS anaerobic metabolism. Lactic acid in CSF may vary independently of the level in the blood. It appears that diffusion of lactic acid across the blood - CSF barrier is very slow.
The measurement of CSF lactate may be useful as a screening test to detect a CNS disease, and may be an aid in the differential diagnosis of bacterial meningitis vs. viral meningitis if other conditions can be excluded.

Lactate dehydrogenase (LD/LDH) in cerebrospinal fluid

Although many different enzymes have been measured in CSF, only lactate dehydrogenase (LDH) appears to be clinically useful. The sources of LDH in normal CSF include diffusion across the blood - CSF barrier, and LDH activity in cellular elements of CSF such as leukocytes, bacteria, and tumor cells. Because the brain tissue is rich in LDH, a damaged CNS tissue can cause increased levels of LDH in the CSF. Measurement of LDH in the CSF has been used for differential diagnosis of bacterial vs. viral meningitis.

Total protein in cerebrospinal fluid

CSF proteins originate primarily from the ultrafiltration of plasma across the choroidal capillary wall though some proteins are peculiar to CSF and are synthesized in the CNS. The ultrafiltration process removes most plasma proteins so that the total protein concentration in CSF (150 to 450 mg/L) is much lower than that in serum (60 to 78 g/L).

Globulins in cerebrospinal fluid

A negative reaction to globulin does not exclude pathologic changes of CSF proteins, but a positive reaction is always a sign of more severe pathological changes in the BBB permeability.

CSF protein electrophoresis

Normally, CSF protein can only be detected on electrophoresis after specimen concentration. Normal CSF protein differs from serum in having lower a2-globulins, low complement and an extra transferrin band; immunoglobulins are much lower than in serum, while prealbumin represents about 5% of total CSF protein.

Albumin in cerebrospinal fluid

Albumin is a particularly suitable indicator protein because it is neither synthesized nor metabolized intrathecally. In CSF that is free of contaminating blood, albumin must necessarily have come from plasma through the BBB. Albumin is the most prevalent protein in normal CSF (55% to 75% of total).

IgG immunoglobulin in cerebrospinal fluid

The "major" immunoglobulins in CSF are IgG, IgA, and IgM. Of all these immunoglobulins, IgG is quantitatively most important. The increase of IgG in CSF has been noticed in many neurologic diseases. It may be the result of different processes occurring simultaneously or quite independently of others.

Blood-brain barrier

The barrier between the brain and the blood that allows the brain to maintain a CSF composition different from that of blood. CSF normally contains very little protein because the protein in blood serum is in the form of large molecules that cannot cross the BBB. However, the proportion of albumin to globulin is higher in CSF than in blood plasma, since the albumin molecule is significantly smaller and can more easily cross the BBB.

VDRL test for syphilis

Serum antibodies do not usually penetrate the BBB; thus the presence of treponemal and non-treponemal antibodies in the CSF usually indicates CNS syphilis. Although VDRL test on CSF lacks sensitivity, false positive reactions are rare.

Microscopic examination of CSF cells

Cells in cerebrospinal fluid
Erythrocytes (red cell counts)
Leukocites (white cell counts)
Other cells

Cells in cerebrospinal fluid

Spinal fluid obtained by lumbar puncture is examined for the presence of abnormal cells and for an increase or decrease in the normally present cell population. Most of the usual laboratory procedures for the study of CSF involve examination of white cells and white blood cell count: chemical and microbiological studies are also performed. In recent years, cell studies of the CSF have been used to identify neoplastic cells. These studies have proved especially helpful in the diagnosis and treatment of the different phases of leukemia disorders.

Erythrocytes (red cell counts)

CSF is essentially free from cells. There are normally not erythrocytes present in CSF. The red cell count done on CSF is of limited diagnostic use in most instances

Leukocites (white cell counts)

CSF is essentially free from cells. When the cells are counted, they are identified by cell type, and the percentage of cell type is compared to the total number of white cells present. In general, inflammatory disease, hemorrhage, neoplasm, and trauma will cause an elevated cell count.

Other cells

  • Malignant cells (lymphocytes or histiocytes) may be present in primary and metastatic brain tumors, especially with meningeal extension.
  • Increased numbers of plasma cells may occur in association with lymphocytic reactions.
  • Macrophages are present in traumatic and ischemic cranial infarcts, tuberculous or mycotic meningitis, reaction to erythrocytes, foreign substances, or lipids in the CSF.
  • Glial, ependymal, and plexus cells may be present after surgical procedures or trauma to the CNS.
  • Leukemic cells occur in CSF after several remissions have been achieved by chemotherapy. Leukemic cells may occur in CSF during apparent remission and after chemotherapy has been discontinued.

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