Liquor Diagnostics
To detect meningitis, lumbar puncture and examination of the cerebrospinal fluid is an absolute standard procedure. However, the type of meningitis is reflected in the individual laboratory values. It is therefore important to know that meningitis can be caused by bacteria as well as viruses and fungi.
Typical bacterial pathogens are meningococci, pneumococci, staphylococci etc. Among the viruses are herpes, enteroviruses and TBE. Already macroscopically signs of meningitis can be identified in the cerebral fluid.
A cloudiness of the cerebrospinal fluid indicates an increased cell count and protein content. The bacteria themselves can also cloud the cerebrospinal fluid. If the white blood cell content is particularly high, the cerebrospinal fluid may even appear purulent.
For a more detailed examination, the cerebrospinal fluid is first examined microscopically to determine the cell count and, if necessary, to make bacteria visible with the help of a Gram stain. It should be noted, however, that in the case of bacterial meningitis, bacteria are not always found in the cerebrospinal fluid. Furthermore, treatment with antibiotics can make the search even more difficult.
If the number of bacteria is below the detectable limit, a culture is usually applied. However, this can take up to 3 days. In order to distinguish which type of pathogen causes meningitis, the individual white blood cells are examined more closely and their number determined.
If bacterial meningitis persists for a longer period of time, an increased number of neutrophil granulocytes can be found in the cerebral fluid. In case of viral meningitis, the lymphocyte count is increased. For the diagnosis of a viral infection, modern laboratory procedures such as the so-called polymerase chain reaction are increasingly used.
The rather rare fungal infection of the meninges can be detected by a high content of eosinophil granulocytes. In addition to microscopic examination of the cerebral fluid, clinical chemistry is also of great importance for diagnostics. In this context, one pays particular attention to the total protein, as well as to glucose and lactate concentration.
In meningitis, the total protein is increased, glucose is decreased and lactate is increased. This is because more antibodies are formed and glucose is broken down more strongly, which in turn results in lactate.
