Type of test Blood, urine, stool, throat, skin lesions
Normal findings
No virus isolated
Test explanation and related physiology
Viral infections are the most common infections affecting children and adults. Viruses are subdivided by the nucleic acid material they contain (RNA or DNA). Infections from viruses are often indistinguishable from bacterial infections. Definitive diagnosis of viral disease is made by culture of the virus (discussed here). Other methods used to identify viral disease include:
• Serologic methods of identifying antibodies to a specific virus
• Serologic methods of identifying antigen parts of a virus
• Direct detection by electron microscopy
• Detection by nucleic acid probes/viral load
The ability to isolate a virus in culture depends on many aspects of the culture process. The first is determining the correct specimen for culture. That depends on the organ involved and the type of virus suspected (Table 1). Timing is important. Viral load is always the greatest in the early stages of the disease. This can now be measured by direct quantification of viral DNA or RNA. Cultures obtained in the first few days after symptoms appear offer the best chance of identifying the infective culture. Viral cultures take 1 to 2 days to be reported.
Table1. Specimen culture for common viruses and diseases
Interfering factors
• An inadequate specimen, the timing, or the choice of culture medium will cause false-negative test results.
• The use of a cotton swab or wooden applicator for specimen collection may destroy the virus.
Procedure and patient care
Before
* Explain the method of collection of the specimen to the patient.
• Obtain a history regarding the timing of symptoms.
• Accurately record the source of the specimen.
During
• Use a closed specimen system to obtain and transport the specimen to the laboratory.
• Transport the specimen immediately to the laboratory. Viruses in specimens quickly lose their vitality.
• Place samples on ice if delivery to the laboratory is not immediate.
• Small-volume specimens such as tissue aspirates are often best transported in viral transport medium. If bacterial cultures are to be performed, collect as a separate specimen.
• If blood is the specimen, obtain 5 mL to 7 mL of blood in a lavender- or blue-top tube.
After
* Explain that the patient may still be infectious and should minimize exposure to others.
Abnormal findings
Viral infectious disease (see Table 1)
