Serological studies of piperacillin antibodies

BACKGROUND: Penicillin‐induced immune hemolytic anemia (IHA) is associated with immunoglobulin G antipenicillin detected by testing penicillin‐coated red blood cells (RBCs). Antibodies to piperacillin, a semisynthetic penicillin, would be expected to react similarly; however, antipiperacillin can be detected by testing in the presence of the drug. Piperacillin is commonly used in combination with tazobactam, which causes nonimmunologic protein adsorption onto RBCs. In six cases of piperacillin‐induced IHA, reactivity with piperacillin‐coated RBCs was not similar to reactivity of antipenicillin with penicillin‐coated RBCs. STUDY DESIGN AND METHODS: Antipiperacillin was tested against piperacillin‐coated RBCs prepared using different pH buffers. Plasma from blood donors and sera/plasma from patients were tested with piperacillin‐coated, penicillin‐coated, and uncoated RBCs. Hapten inhibition studies were performed using different concentrations of piperacillin. Donors' plasma were tested in the presence of piperacillin; sera from patients with IHA were tested in the presence of tazobactam. RESULTS: Piperacillin required high pH for binding to RBCs. Agglutination of piperacillin‐coated RBCs was observed in 91 percent of donors' and 49 percent of patients' plasma and was inhibited by piperacillin. In contrast to patients with IHA due to piperacillin, donors' plasma tested in the presence of piperacillin did not react. Tazobactam antibodies were not detected. CONCLUSION: A high percentage of donors' and patients' plasma contain an antibody to piperacillin or a chemically related structure detected by testing with piperacillin‐coated RBCs. A diagnosis of piperacillin‐induced IHA should not be made solely on the reactivity of a patient's plasma/serum with piperacillin‐ or piperacillin/tazobactam‐coated RBCs; testing in the presence of piperacillin is more reliable.