General Specimen Handling
Please refer to the specific Virology Lab Test for a detailed description of the appropriate collection and handling of specimens. Listed below are a number of general points to consider when obtaining specimens for viral diagnosis:
- Appropriate specimen collection and handling is absolutely critical to the success of laboratory testing for diagnosis of viral infections
- Specimens that are poorly collected, ill timed, or improperly handled during the time between collection and testing are more likely to yield incorrect test results.
- Specimens for direct detection of viruses should be collected as close to clinical onset as possible (e.g., within the first 1-3 days) since viral titers are highest at this time. Acute viral infections are self-limiting and are cleared within the first 5-10 days of illness. Therefore, nothing is gained by a delay in taking a specimen. Duration of viral shedding and the amount of virus present will vary, however, depending on the virus, the immunocompetence of the host, the age of the patient, the anatomical site or source of the specimen, and whether there is systemic or local involvement. Young infants, immunocompromised children and adults, individuals with underlying dysfunctions, and the elderly may shed virus for more extended times.
- The specimen site should be determined by the clinical presentation and the pathogenic potential of the suspected virus.
- Recovery of a given virus may be enhanced by collecting the same specimen type over a period of several days or by collecting multiple specimens from different body sites. Consult the laboratory for additional information.
- Specimens should be transported to the laboratory as quickly as possible after collection, since some viruses, particularly those with envelopes (e.g. herpes group viruses, most respiratory viruses), are quite labile outside their natural host and rapidly lose infectivity. Nonenveloped viruses, such as adenoviruses and enteroviruses, on the other hand, are more stable and maintain their infectivity for longer periods of time. When immediate transport is not possible, specimens should be kept refrigerated or on wet ice. If delays greater than 24-48 hours are anticipated, specimens should be processed as needed and then immediately frozen to -70°C and transport to the laboratory on dry ice. In general, specimens to be used for the direct detection of viruses (e.g., culture, antigen assays, or molecular methods) should not be stored at room temperature or frozen at -20°C. It is acceptable to freeze serum or plasma at -20°C for transport to and extended storage in the laboratory when used for detection of viral-specific antibodies.
- Specimens for molecular testing (e.g., PCR) should be collected and transported in such a manner as to ensure the stability and amplification of the nucleic acids. This is particularly true when collecting and transporting specimens to detect RNA viruses; RNA is a very unstable molecule and is extremely susceptible to degradation by RNases that are ubiquitous in the environment. Therefore, specimens for molecular testing should be stored at 4ºC immediately after collection and then transported to the Virology Laboratory without delay.
- When using swabs for collecting specimens from dermal, rectal, respiratory, and ocular sites, plastic- or metal-shafted swabs with rayon, Dacron, cotton or polyester tips are preferred; calcium alginate or wooden shafted swabs are inhibitory to some viruses and are not acceptable.
- All swab and tissue specimens should be placed in viral transport medium immediately after collection. Viral transport medium is available from the Virology Laboratory and Central Laboratory Services upon request. Bacteriological transport medium should not be used to transport specimens for viral diagnosis.
- Urine, stool, cerebrospinal fluid, and other body fluid specimens should be submitted to the laboratory in sterile, leak-proof containers. Do not dilute these specimens in viral transport medium.
- Whole blood specimens should be collected in a suitable anticoagulant. EDTA is currently the preferred anticoagulant for most viral studies that require plasma or white blood cells and is considered to be the best stabilizer of nucleic acids for molecular testing.
- For viral serological assays, serum is the preferred specimen. Blood should be collected without the use of anticoagulants or preservatives. A single serum specimen is sufficient to determine the immune status of an individual or for the detection of virus-specific IgM antibody. With few exceptions (e.g., Epstein-Barr virus, hepatitis B virus, parvovirus B19), paired acute and convalescent serum specimens collected 10-14 days apart are needed for the diagnosis of current or recent viral infections when specimens are tested for virus-specific IgG antibody. The acute-phase serum should be collected as early as possible in the course of the illness, and the acute and convalescent sera should be tested simultaneously to obtain the most meaningful results. Serum specimens from mother, fetus, and newborn can be submitted for the evaluation of IgG and IgM antibodies for detection of prenatal, natal, and postnatal viral infections. Plasma can be used as an acceptable alternative to serum for serological diagnosis of HIV and hepatitis viruses.
- When submitting specimens to the laboratory, the labeling of specimens must fulfill the requirements as defined in Hospital Policy #PE-4-02 (PDF) found in the Patient Care Manual. The specimen container should be labeled with the patient's full name, the medical record number or other unique identifier, the date and time of collection, and the full name of the collector. Each specimen should be accompanied by a requisition slip containing the same information as on the specimen container as well as the patient’s location within the hospital, test(s) requested, source of specimen, requesting physician with pager or extension number, and suspected clinical diagnosis.
- Please consult the Virology Laboratory for questions or information on the preferred methods and materials needed for obtaining specimens for viral diagnosis.