Specific antibodies can be detected in serum and other body fluids (e.g., synovial fluid, cerebrospinal fluid [CSF]).
Procure samples. For diagnosis of infectious disease, a blood sample (serum preferred) using a 7-mL red-topped tube should be obtained at illness onset (acute phase), and the other sample should be drawn 3–4 weeks later (convalescent phase). In general, serologic test usefulness depends on a titer increase in the time interval between the acute and the convalescent phase. For some serologic tests, one serum sample may be adequate if the antibody presence indicates an abnormal condition or the antibody titer is unusually high. see Appendix A for standard precautions.
Perform the serologic test before doing skin testing. Skin testing often induces antibody production and could interfere with serologic test results.
Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag. Send samples to the laboratory promptly. Hemolyzed samples cannot yield accurate results. Hemoglobin in the serum sample can interfere with complement-fixing antibody values.