Hyphae can occasionally be seen in Candida or other fungal meningitis cases. Several factors influence the sensitivity of Gram stain. Laboratory techniques used to concentrate and stain CSF can greatly influence reliability. Cytocentrifugation increases the ability to detect bacteria. Staining will be positive in 25 percent of cases if fewer than 1, CFU per mm 3 are present, and in 75 percent of cases if more than , CFU per mm 3 are present.
Up to 10 percent of initial Gram stains are misread. Acid-fast staining should be done if tuberculosis is clinically suspected. Only 37 percent of initial smears will be positive for acid-fast bacilli. This result can be increased to 87 percent if four smears are done.
Other stains should be performed if indicated by the situation. Cryptococcus may be identified up to 50 percent of the time on an India ink preparation. A tap-water control should always be done to ensure that the India ink is not contaminated. Toxoplasmosis can be diagnosed with Wright or Giemsa stain. A simple wet preparation of CSF under a cover slip can yield positive results in a variety of protozoan and helminthic infections.
Newborn patients have up to mg per dL 1. Protein concentration is falsely elevated by the presence of RBCs in a traumatic tap situation.
This can be corrected by subtracting 1 mg per dL 0. Adapted with permission from Fishman RA. Cerebrospinal fluid in diseases of the nervous system. Philadelphia: Saunders, Low CSF protein levels can occur in conditions such as repeated lumbar puncture or a chronic leak, in which CSF is lost at a higher than normal rate.
CSF protein levels do not fall in hypoproteinemia. A true normal range cannot be given for CSF glucose. As a general rule, CSF glucose is about two thirds of the serum glucose measured during the preceding two to four hours in a normal adult.
This ratio decreases with increasing serum glucose levels. CSF glucose levels generally do not go above mg per dL CNS infections can cause lowered CSF glucose levels, although glucose levels are usually normal in viral infections Table 2.
Chemical meningitis, inflammatory conditions, subarachnoid hemorrhage, and hypoglycemia also cause hypoglycorrhachia low glucose level in CSF. Elevated levels of glucose in the blood is the only cause of having an elevated CSF glucose level. There is no pathologic process that causes CSF glucose levels to be elevated.
Cultures done on 5 percent sheep blood agar and enriched chocolate agar remain the gold standards for diagnosing bacterial meningitis. Enterovirus, the leading cause of viral meningitis, can be recovered in 40 to 80 percent of cases. Culture for herpes simplex virus is 80 to 90 percent sensitive but can take five to seven days to become positive.
Mycobacterium tuberculosis is best grown using multiple large volume samples of CSF. Culture is positive 56 percent of the time on the first sample, and improved to 83 percent of the time if four separate samples are cultured.
These cultures often take up to six weeks for positive identification. Fungal cultures are positive in more than 95 percent of Cryptococcus neoformans cases and in 66 percent of candidal meningitis cases. Other fungi are less likely to be culture positive. Sensitivity varies greatly between bacteria. LA for Haemophilus influenzae has a sensitivity of 60 to percent, but is much lower for other bacteria.
The specificity for LA is very low. Some experts suggest using LA in cases of suspected bacterial meningitis if the initial Gram stain and bacterial culture are negative after 48 hours. Polymerase chain reaction PCR has been a great advance in the diagnosis of meningitis.
Although testing is expensive, there is a potential for cost savings by decreasing overall diagnostic testing and intervention. PCR has been especially useful in the diagnosis of viral meningitis. PCR of the CSF has a sensitivity of 95 to percent, and a sensitivity of percent for herpes simplex virus type 1, Epstein-Barr virus, and enterovirus. PCR has a sensitivity of 54 to percent and a specificity of 94 to percent for tuberculous meningitis, and could replace acid-fast bacillus smear and culture as the test of choice.
Already a member or subscriber? Log in. Interested in AAFP membership? Learn more. MARK M. Address correspondence to Dean A. Seehusen, M. E, Sumner, WA e-mail: dseehusen msn.
Reprints are not available from the authors. The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U.
Army Medical Corps or the U. Army at large. The authors indicate that they do not have any conflicts of interest. Sources of funding: none reported. Cerebrospinal fluid physiology and the management of increased intracranial pressure. Mayo Clin Proc. Fishman RA. Khurana RK. Updated December 31, Improving the brain delivery of chemotherapeutic drugs in childhood brain tumors. Cancers Basel. CSF Analysis. Updated November 6, Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth.
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How Mumps Is Diagnosed. Ventricular System: Anatomy, Function, and Treatment. What Is an Ependymoma? How Burkitt Lymphoma Is Diagnosed. Symptoms of Ependymoma. The Different Types of MS. Mollaret Meningitis. CSF is a clear fluid that surrounds and protects the brain and spinal cord. The tests may look for proteins, sugar glucose , and other substances.
A sample of CSF is needed. A lumbar puncture , also called a spinal tap, is the most common way to collect this sample. Less common ways to take a fluid sample include:. After the sample is taken, it is sent to the laboratory for evaluation. Your doctor will ask you to lie flat for at least one hour after the lumbar puncture. You may develop a headache after the lumbar puncture.
If it happens, drinking caffeinated beverages such as coffee, tea or soda may help. Your health care provider will tell you how to prepare for lumbar puncture. Analysis of CSF can help detect certain conditions and diseases. All of the following can be, but are not always, measured in a sample of CSF:. Normal value ranges may vary slightly among different laboratories.
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