Diagnosis of infectious mononucleosis, caused by Epstein-Barr virus (EBV), depends on serologic (antigen-antibody) confirmation of clinical manifestations of the disease that include fever, sore throat, and lymphadenopathy. EBV stimulates the formation of new antigens that, in turn, stimulate a humoral and cellular immune response. The humoral response is characterized by an increased titer of the antibodies IgG and IgM early in the disease. The cellular response is characterized by the activation of T cells later in the illness in response to the EBV-induced infection.

The hallmark of EBV infection is the heterophil antibody, also called the Paul-Bunnell antibody, the formation of which is stimulated by the virus. The heterophil antibody is an IgM that agglutinates sheep or horse red cells. Forssman antibody, which can be present in the serum of normal people as well as in that of individuals with serum sickness, also agglutinates with sheep erythrocytes. The Davidsohn differential absorption test can be used to distinguish between the Paul-Bunnell antibody and the Forssman antibody. Currently, more rapid and sensitive tests are available that use red blood cells from horses in a single-step agglutination test.³¹ These tests (e.g., Monospot, Monoscreen) are used as screening tests for infectious mononucleosis and are gradually replacing the more traditional techniques.

• Negative, or a titer of less than 1:56 heterophile antibodies

• False-positive results may occur in the presence of narcotic addiction, serum sickness, lymphomas, hepatitis, leukemia, cancer of the pancreas, and phenytoin therapy.

Indication for Infectious Mononucleosis Tests

• Suspected infectious mononucleosis (Of individuals with EBV infectious mononucleosis, 95 percent will have a positive result, 86 percent in the first week of illness.)

Nursing Care Before the Procedure

Client preparation is the same as that for any study involving the collection of a peripheral blood sample (see Appendix I).

• A thorough history should be obtained to identify possible sources of false-positive results.

A venipuncture is performed and the sample collected in a red-topped tube. For screening tests, the directions accompanying the test kit are followed. For traditional tests, the sample should be sent to the laboratory promptly.

Nursing Care After the Procedure

Care and assessment after the procedure are the same as for any study involving the collection of a peripheral blood sample.

• Abnormal values: Note and report increased heterophile titer or titers against EBV. Assess signs and symptoms of infection such as fever, chills, malaise, sore throat, anorexia, enlarged lymph nodes, and fatigue. Provide rest, adequate nutritional and fluid intake, and activities that do not cause fatigue or stress.