Respiratory Syncytial Virus Antibodies

Respiratory syncytial virus (RSV), a member of the pararnyxovirus group, is the major viral cause of severe lower respiratory tract disease in infants but may cause infections in people of any age. RSV infections are most common and produce the most severe disease during the first 6 months of life. Initial infection involves viral replication in epithelial cells of the upper respiratory tract, but in younger children especially, the infection spreads to the bronchi, the bronchioles, and even the parenchyma of the lungs.

In this test, immunoglobulin G (lgG) and IgM class antibodies are quantified using indirect immunofluorescence.

Purpose

• To diagnose infections caused by RSV

Patient preparation

• Explain to the patient (or, to the patient's parents) the purpose of the test.
• Tell the patient or parents that the test requires a blood sample and who will perform the venipuncture and when.
• Reassure the patient that although he may experience transient discomfort from the needle puncture and the tourniquet, collecting the sample takes less than 3 minutes.

Procedure and posttest care

• Perform a venipuncture, and collect 5 ml of sterile blood in a red-top tube.
• Allow the blood to clot for at least 1 hour at room temperature.
• If a hematoma develops at the venipuncture site, apply warm soaks.

Precautions

• Handle the sample gently to prevent hemolysis.
• Transfer the serum to a sterile tube or vial, and send it to the laboratory promptly.
• If transfer must be delayed, store the serum at 39.2° F (4° C) for 1 to 2 days or at -4° F (-20° C) for longer periods to avoid contamination.

Reference values

Sera from patients who have never been infected with RSV have no detectable antibodies to the virus (less than 1:10).

Normal findings

Normal serum is negative for HBsAg.

Abnormal findings

The qualitative presence of IgM or a fourfold or greater increase in IgG antibodies indicates active RSV infection. Note that, in infants, serologic diagnosis of RSV infections is difficult because of the presence of maternal IgG antibodies. Thus, the presence of IgM antibodies is most significant.

Interfering factors

• Hemolysis due to rough handling of the sample
• Failure to store serum at the proper temperature