The Significance of Anti-Platelet Antibodies Associated with Antibiotic Use, A Descriptive Analysis.

Abstract Abstract 4470 Introduction Antibiotics (Abx) have been implicated in immune thrombocytopenia via drug dependent platelet antibodies (DDPA). Our institution has had a DDPA assay available since 1994 which is used to guide clinical decisions. We performed a retrospective review to determine the significance of DDPA. Methods We reviewed the medical records of patients (pts) who tested positive for abx DDPA between 1994 and 2006 and performed a descriptive analysis. Detection of DDPAs was performed using a previously described, modified solid phase red cell adherence assay that detects hapten or immune complex reactions. Results A total of 71 pts were included in this analysis. Multiple classes of abx were tested. Platelet nadir was <50 in 70%, between 50 and 100 in 26% and over 100 in 4% of pts. Pts had between 1 and 4 abx tested: 37% had 1, 37% had 2, 15% had 3, and 11% had 4 tested; 65% of pts had one abx positive and 35% had >1 abx positive for DDPA. Of those with >1 abx tested (n=45), 14 (31%) had all tested abx positive. 53% of abx testing took place on or after the abx stop date and 32% of abx tested were administered for <=3 days. Only 29 of 38 pts receiving heparin were tested for heparin-associated antibodies, and 14 had positive results. 49 pts had other non-abx drugs tested, 19 with positive DDPA. Thus, 35% had alternative non-abx testing positive for DDPA. 31% of pts had bleeding complications and 35% of pts died during hospitalization. Excluding pts who died and those with non-abx positive DDPA left 25 pts, median platelet counts were: abx start=142; nadir=22, abx discontinuation=46, hospital discharge=192. Conclusions Antibiotic DDPA testing is usually performed in ill pts with multiple medical complications and comorbidities. Abx were stopped for concern of DDPA in a number of pts for whom typical immune thrombocytopenia was not present or alternative explanations could be found. Though some pts exhibited improvement in platelet count after abx were stopped, a clear understanding of which pts may benefit from DDPA testing could not be determined based on the retrospective nature of this study and the complexity of pts histories. Further research is necessary to clarify the clinical applicability of DPPA testing. Disclosures: Szczepiorkowski: Cersus Corporation: Research Funding; CaridianBCT: Research Funding; BASF: Research Funding; Terumo Corporation: Research Funding; Fenwel, Inc - Scientific Advisory Board: Research Funding.