A fluorescent antibody is a protein that has a fluorescent dye attached to it and glows when viewed under a microscope. This enables a technician to determine whether or not a sample presented for evaluation contains antibodies. The testing is qualitative in nature and does not allow for antibody counting, allowing labs to provide a positive or negative result without knowing how many antibodies are present. Testing can help with disease diagnosis, including postmortem examinations of patients with infections.
Fixing cells from the sample to a slide is the first step in the fluorescent antibody staining procedure. The cells are washed in a solution with antigens bound to fluorescent tags. If the antigens are compatible with the antibodies on the slide, they will lock on, attaching and remaining in place. The technician can view the sample under the microscope with a special filter and only see the fluorescence. If the slide lights up, this means antibodies are present; if it doesn’t, the test is negative.
This test can be used to evaluate suspected rabies cases, for example. Because the virus cannot be detected in the bloodstream, tissue from the brain must be examined. Technicians can use a small sample of cells to perform a fluorescent antibody test, looking for the telltale bright green color associated with rabies. If a doctor suspects a lung infection such as Legionnaire’s disease, he or she may request this testing on sputum from the patient’s lungs.
To ensure that the testing is valid, technicians employ a number of failsafes. Repeating positive tests to ensure antibodies are present and controlling samples to reduce the risk of cross-contamination are examples of this. When using the fluorescent antibody test, detailed lab instructions are followed to the letter to ensure that it is repeatable and follows a specific recognized protocol. Samples that are in doubt can be sent to a third-party lab for verification.
This test may be referred to as DFA (Direct Fluorescent Antibody) by patients. The cost of the test varies depending on the organisms being tested for and the pricing scheme used by the lab. It is usually covered by insurance, and patients may be eligible for free testing through public health agencies in some cases. People who are exposed to a disease outbreak, for example, may be subjected to extensive testing in order to learn more about the infection. Because it is considered a public health service, it may be funded by government agencies.