title: Negativization rates of IgE radioimmunoassay and basophil activation test in immediate reactions to penicillins.
abstract: BACKGROUND
  Skin test sensitivity in patients with immediate allergy to penicillins tends to decrease over time, but no information is available concerning in vitro tests. We analysed the negativization rates of two in vitro methods that determine specific immunoglobulin E (IgE) antibodies, the basophil activation test using flow cytometry (BAT) and the radioallergosorbent test (RAST), in immediate allergic reactions to penicillins.
  
  
  METHODS
  Forty-one patients with immediate allergic reactions to amoxicillin were followed up over a 4-year period. BAT and RAST were performed at 6-month intervals. Patients were randomized into groups: Group I, skin tests carried out at regular intervals; Group II, skin tests made only at the beginning of the study.
  
  
  RESULTS
  Differences were observed between RAST and BAT (P < 0.01), the latter showing earlier negativization. Considering different haptens, significant differences for the rate of negativization were only found for amoxicillin (P < 0.05). Comparisons between Groups I (n = 10) and II (n = 31) showed a tendency to become negative later in Group I with RAST.
  
  
  CONCLUSIONS
  Levels of specific IgE antibodies tended to decrease over time in patients with immediate allergic reactions to amoxicillin. Conversion to negative took longer for the RAST assay, although the differences were only detected with the amoxicillin hapten. Skin testing influenced the rate of negativization of the RAST assay, contributing to maintenance of in vitro sensitivity. Because of the loss of sensitivity over time, the determination of specific IgE antibodies to penicillins in patients with immediate allergic reactions must be done as soon as possible after the reaction.
authors.affiliation: Research Unit for Allergic Diseases, Carlos Haya Hospital, Málaga, Spain.
authors.forename: T D
authors.initials: TD
authors.lastname: Fernández
authors.forename: M J
authors.initials: MJ
authors.lastname: Torres
authors.forename: N
authors.initials: N
authors.lastname: Blanca-López
authors.forename: J L
authors.initials: JL
authors.lastname: Rodríguez-Bada
authors.forename: E
authors.initials: E
authors.lastname: Gomez
authors.forename: G
authors.initials: G
authors.lastname: Canto
authors.forename: C
authors.initials: C
authors.lastname: Mayorga
authors.forename: M
authors.initials: M
authors.lastname: Blanca
mesh_terms: D000328:Adult; D000368:Aged; D000900:Anti-Bacterial Agents / Q000009:adverse effects / Q000276:immunology*; D015549:Basophil Degranulation Test; D001491:Basophils / Q000276:immunology* / Q000378:metabolism; D004342:Drug Hypersensitivity / Q000175:diagnosis* / Q000276:immunology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006969:Hypersensitivity, Immediate / Q000175:diagnosis* / Q000276:immunology; D007073:Immunoglobulin E / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010406:Penicillins / Q000009:adverse effects / Q000276:immunology*; D011852:Radioallergosorbent Test
chemical_list: D000900:Anti-Bacterial Agents; D010406:Penicillins; D007073:Immunoglobulin E