[PubMed] [Google Scholar] 33. and polysorbate 80. Plasma samples were positive for anti-PEG specific IgE and IgG antibodies only in cases and binding increased directly proportional to the molecular weight of PEG tested. FDA adverse event reports revealed 53 additional cases of possible PEG 3350 anaphylaxis. Conclusions: Immediate hypersensitivity to TGFA PEG 3350 with cross-reactive polysorbate 80 hypersensitivity may be under recognized in clinical practice and can be detected with clinical skin testing. Our studies raise the possibility of an IgE mediated Boc-NH-PEG2-C2-amido-C4-acid Type I hypersensitivity mechanism in some cases. asparaginase (Oncaspar) at 10 g/ml. For anti-PEG IgG detection, plasma obtained from the aforementioned 2 cases 2~3 months after their last anaphylaxis episodes were incubated at 1:400 dilution. For anti-IgE detection, the same plasma samples were pretreated with Protein G Plus Agarose (Thermo Fisher Scientific) at 1:1 ratio to remove IgG, then Boc-NH-PEG2-C2-amido-C4-acid incubated at 1:10 dilution. HRP-conjugated goat anti-human IgG (Sigma) or anti-human IgE (BioRad) antibodies were added at 1:1000 and 1:10,000 dilution respectively. Plates were read Boc-NH-PEG2-C2-amido-C4-acid at dual wavelengths of 490 nm and 630 nm on an ELx808 microplate reader (BioTek). Plasma samples from 6 patients with similar exposure to colonoscopy preparations containing macrogols were used as controls. To better determine the presence or absence of PEG specific IgE, we next used an electrochemiluminescent method with greater sensitivity for detection. Standard MULTI-ARRAY 96-well SECTOR plates were coated with Oncaspar and 5,000g/mol methoxy-PEG-bovine catalase at 10 g/ml. Samples were processed with Protein G Plus Agarose as described above, then incubated at 1:10 dilution. Biotin-conjugated goat anti-human IgE (BioRad) antibody was added at 1:10,000 dilution. SULFO-TAG labeled Streptavidin was used as the detection reagent. Plates were read with a Sector Imager 6000 Analyzer (Meso Scale Discovery). Furthermore, to investigate the effect of the molecular size of unconjugated PEG on anti-PEG specific IgG binding, we coated Nunc Maxisorp 96-well microplates (Thermo Fisher Scientific) with 5g/ml HO-PEG-NH2 of MW ranging from 1kDa to 10 kDa (Creative PEGWorks). Case and control samples were incubated at 1:100 dilution. Other steps were the same as the anti-Oncaspar IgG detection ELISA aforementioned. Public Data Review: To evaluate the scope to which polyethylene glycol 3350 might be associated with anaphylaxis in the United States, we next undertook a review of the publicly available FDA Adverse Event Reporting System (FAERS) database from 1989 through 2017. Using the search terms polyethylene glycol and anaphylactic shock or Boc-NH-PEG2-C2-amido-C4-acid anaphylactic reaction we reviewed the number of these complaints for polyethylene glycol containing colonoscopy preparations and laxative products. We evaluated cases associated with branded and generic colonoscopy and laxative products whose primary ingredient was PEG 3350, including colonoscopy products both with and without electrolytes. Medication Excipient Review: To evaluate the degree to which immediate hypersensitivity to PEG 3350 or polysorbate 80 might affect medication or vaccine safety for affected patients, we next reviewed publicly available data in the searchable DailyMed database provided by the National Library of Medicine,4 which allows for search queries targeting both active and inactive ingredients of all FDA approved and over-the-counter (OTC) medications in the United States. Searches conducted on the advanced search feature of this database will return reviewable information on the first 1000 hits. Using this database, we searched with the terms polyethylene glycol 3350 and polysorbate 80, selecting that these ingredients must be either an active or inactive ingredient. We then classified the first 1000 hits by route of administration and indication for the medication. We also reviewed vaccine excipient summaries provided by the CDC for vaccines containing either of the two ingredients.22 Results: Description of Cases: During our 3 year period of surveillance, we encountered two patients with a history of anaphylaxis during preparation for colonoscopy and after methylprednisolone acetate injections. The first such patient was a 57 year old white male with an occupational history as a mechanic and electrician, who presented to our clinic for evaluation of suspected.