CLIA-Waived Microbiology Testing
Learning Objective: Examine CLIA-waived microbiology testing.
Often, growing a pathogen on a nutrient media plate is difficult, and it takes time to grow and isolate the pathogen. A rapid direct immunology test demonstrates the presence of the antigen in a specimen that is placed in a test kit containing its specific antibody. If the pathogen is present, it produces a colored reaction, indicating a positive result.
POLs with appropriate CLIA-waived certification can perform many rapid identification tests for a variety of infectious diseases. Rapid tests are designed to give the provider positive test results quickly and efficiently so that treatment can be started. If the test result is negative, the provider may need to order additional referral laboratory tests:
The first step in performing these tests is to review the package insert provided by the manufacturer. This gives valuable information about the test:
• Principle on which the test is based
• Reagents and equipment needed
• Proper specimen collection techniques
• Patient preparation requirements
• Test procedures
• Any precautions or warnings pertaining to the procedure
The insert also provides information about quality control, interpretation of results, limitations of the procedure, and references.
Rapid Strep Testing
Learning Objective: Describe the process for rapid strep testing.
Rapid strep testing is commonly performed in the POL and can be completed while the patient waits. The patient’s throat is swabbed. The test swab is placed in an extraction well, and the extract is tested for antigens found on the surface of S. pyogenes (also referred to as Group A streptococcus [GAS]). The test kit uses a lateral flow immunoassay. This means that the specimen “flows” into the test area. If the strep A pathogen is present, there will be an antigen-antibody reaction with the group A strep antibodies in the testing area. The reaction of the strep A antigen and the strep A antibodies cause a color change that can be seen (Procedure 35.4).
Negative test results should be confirmed with a throat culture performed in the microbiology laboratory (explained later in the chapter). The rapid strep tests are highly specific, so if the test results are positive, there is confidence that S. pyogenes is present in the sample. If the test results are negative, the organism may not have been present in high enough numbers to be detected. Then, a transport swab should be sent to the microbiology reference laboratory to be cultured.
35.5 Critical Thinking Application
Frankie Burns, a 10-year-old, has a raw, sore throat; fever of 101°F; and just feels awful. Laura is going to collect a throat swab from Frankie for a rapid strep test. What bacteria cause strep throat? What is the scientific name of the bacteria? Which of the two names is the genus, and which of the two names is the species?
Influenza A and B Testing
Learning Objective: Describe the process for influenza A and B testing.
The influenza virus causes influenza, or “the flu.” This is a highly contagious, acute viral infection of the respiratory tract. The infection is highly communicable through respiratory exposure, and outbreaks are typically seen in the fall and winter. Type A viruses usually are more common than type B viruses. Type A viruses typically are associated with epidemics, and type B viruses cause a milder infection. A rapid diagnosis of influenza can help with the decision to give antiviral medications. They should be given early in the infection cycle to be the most effective. CLIA-waived rapid lateral flow immunoassays detect both influenza A and influenza B antigens from nasal washes or nasopharyngeal swabs.
Respiratory Syncytial Virus Testing
Learning Objective: Describe the process for respiratory syncytial virus testing.
Respiratory syncytial virus (RSV) is a major cause of upper and lower respiratory tract infections. It is the major cause of bronchiolitis and pneumonia in children and infants. Outbreaks typically occur yearly in the fall, winter, and spring and can be severe for very young children. The CLIA-waived rapid direct immunoassay for RSV uses a nasopharyngeal swab specimen or nasal washings to detect the virus. Because antiviral agents are available to treat RSV infection, rapid diagnosis can lead to the following:
• Shorter hospital stays
• Reduced need for antibiotic therapy to treat secondary bacterial infection
• Lower cost for hospital care
The tests are intended for children under age 5.