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Penicillin Antibody

Penicillin can be detected on the surface of the RBCs of most patients who are receiving high doses intravenously. Penicillin binding to RBCs is dose related. Approximately 30% of patients taking 1.2 to 2.4 million units per day have penicillin on their RBCs, while RBCs of 100% of patients receiving 10 million units per day are affected. This coating is not by itself injurious to RBCs, but about 3% of patients receiving high dose penicillin develop a high titer anti-penicillin antibody that reacts with RBC-bound penicillin. Penicillin induced hemolytic anemia usually occurs gradually over the course of a week of penicillin therapy.

Agglutination of penicillin-coated RBCs by antibody in the patient's serum or antibodies eluted from their own RBCs indicate the presence of anti-penicillin antibodies. Most patients with penicillin-induced immune hemolytic anemia will also have a strongly positive direct antiglobulin test caused by sensitization of their RBCs with IgG. Occasionally complement may also be detected.

A positive test, by itself, is not an absolute indication to stop penicillin therapy.This action is only necessary when there is evidence of hemolysis. Cessation of penicillin is followed by complete recovery, although mild hemolysis and a mixed field antiglobulin test may persist for several weeks.

Specimen requirement is one 5-mL lavender top (EDTA) tube of blood.

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