Leukoagglutinin Test

This test detects leukoagglutinins ­antibodies that react with white blood cells (WBCs) and may cause a transfusion reaction. These antibodies usually develop after exposure to foreign WBCs through transfusions, pregnancies, and allografts.

If a blood recipient has these antibodies, a febrile nonhemolytic reaction may occur 1 to 4 hours after the start of whole blood, red blood cell, platelet, or granulocyte transfusion. This nonhemolytic reaction (marked by fever and severe chills, sometimes with nausea, headache, and transient hypertension) must be distinguished from a true hemolytic reaction before further transfusion can proceed.

Clinical Alert: The presence of these antibodies in a recipient can cause immune-mediated platelet refractoriness, a condition characterized by failure of the platelet count to increase after platelet transfusion.

The technique used to detect leukoagglutinins is the microlymphocytotoxicity test. In this test, the recipient serum is tested against donor lymphocytes or against a panel of lymphocytes of known HLA phenotype. The antibodies in the recipient serum bind to the corresponding antigen present in the lymphocytes and cause cell membrane injury when the complement is added to the test system. Cell injury is detected by examining the lymphocytes under a microscope. If the lymphocytes don't absorb the added dye, the test is negative. If the lymphocytes show dye uptake, the test is positive.

Purpose

• To detect leukoagglutinins in blood recipients who develop transfusion reactions, thus differentiating between hemolytic and febrile nonhemolytic transfusion reactions
• To detect leukoagglutinins in blood donors after transfusion of donor blood causes a reaction

Patient preparation

• Explain to the patient that this test helps determine the cause of his transfusion reaction.
• Tell him that the test requires a blood sample and who will perform the venipuncture and when.
• Reassure him that although he may experience transient discomfort from the needle puncture and the tourniquet, collecting the sample takes only a few minutes.
• Check the patient's history for recent administration of blood, dextran, or I.V. contrast media.

Procedure and posttest care

• Perform a venipuncture, and collect a sample in a 10-ml red-top tube. The laboratory requires 3 to 4 ml of serum for testing.
• If a hematoma develops at the venipuncture site, apply warm soaks.
• If a transfusion recipient has a positive leukoagglutinin test, continued transfusions require premedication with acetaminophen 1 to 2 hours before the transfusion, specially prepared leukocyte-poor blood, or use of leukocyte removal blood filters to prevent further reactions.

Precautions

• Label the sample with the patient's name, the hospital or blood bank number, the date, and the phlebotomist's initials.
• Be sure to include on the laboratory slip the patient's suspected diagnosis and pregnancy status, any history of blood transfusions, and current drug therapy.
• Note that tests for these antibodies aren't useful in deciding which patients should receive leukocyte-poor blood components; the decision must be based on clinical experience.

Normal findings

Normally, test results are negative: Agglutination doesn't occur because the serum contains no antibodies.

Abnormal findings

A positive result in a transfusion recipient indicates the presence of leukoagglutinins in his blood, identifying his transfusion reaction as a febrile nonhemolytic reaction to these antibodies.

A positive result in a donor indicates the presence of leukoagglutinins in his blood, identifying the cause of a recipient's reaction as an acute, noncardiogenic pulmonary edema.

If a patient is determined to have antibodies or develops the immune-mediated destruction of transfused platelets, he may require special matched blood products for subsequent transfusions.

Interfering factors

• Previous administration of blood, dextran, or I.V. contrast media (causing aggregation resembling agglutination)