Bacterial Meningitis Antigen

This test can detect specific antigens of Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type B, the principal etiologic agents in meningitis. It can be performed on samples of serum, cerebrospinal fluid (CSF), urine, pleural fluid, and joint fluid, but CSF and urine are preferred.

Purpose

• To identify the etiologic agent in meningitis
• To aid diagnosis of bacterial meningitis
• To aid diagnosis of meningitis when the Gram-stained smear and culture are negative

Patient preparation

• As appropriate, explain the purpose of the test to the patient.
• Inform the patient that this test requires a specimen of urine or CSF.
• If a CSF specimen is required, describe how it will be obtained.
• Tell him who will perform the procedure and when and that he may experience transient discomfort from the needle puncture.
• Advise the patient that a headache is the most common complication of lumbar puncture but that his cooperation during the test minimizes such an effect.
• Make sure the patient or a family member has signed an informed consent form.

Procedure and posttest care

• Collect a IO-ml clean-catch specimen of urine or a 1-ml specimen of CSF in a sterile container. (For detailed instructions on collecting a CSF specimen.

Precautions

• Maintain specimen sterility during collection.
• Wear gloves when obtaining or handling the specimen.
• Make sure the cap is tightly fastened on the specimen container.
• Place the specimen on a refrigerated coolant and send it to the laboratory promptly.

Normal findings

Normally, results are negative for bacterial antigens.

Abnormal findings

Positive results identify the specific bacterial antigen: S. pneumoniae, N. meningitidis, H. influenzae type B, or group B streptococci.

Interfering factors

• Previous antimicrobial therapy
• Failure to maintain sterility during specimen collection
• Failure to keep specimen cool
• Failure to send the specimen to the laboratory immediately