title: Analytical performance characteristics of the T4 method in the Abbott AxSYM immunoassay analyzer.
abstract: OBJECTIVE
  To evaluate the tetraiodothyronine (T4) method in the Abbott AxSYM immunoassay analyzer.
  
  
  METHODS
  The single-value criteria proposed by Westgard et al. were employed. Assays of control materials established random error (RE) analytical sensitivity, and linearity. Constant error (CE) was established by studying the effects of interferents on T4 quantification. The AxSYM random access immunoassay analyzer was compared with TDx batch analyzer to determine systematic error (SE). Critical concentrations of T4 are 3.0 micrograms/dL and 13.0 micrograms/dL, as these concentrations represent medical decision points. Allowable error at these critical concentrations are 1.0 and 2.6, respectively.
  
  
  METHODS
  Peninsula Regional Medical Center Clinical Laboratories.
  
  
  RESULTS
  Based on Health Care Financing Administration [HCFA] allowable error goals, RE, SE, and CE were acceptable for concentrations of T4 ranging from 3.0 micrograms/dL to 13 micrograms/dL. PE was virtually absent. Total error (TE) = RE + SE was acceptable at 13 micrograms/dL but exceeded allowable error at the lower critical value of 3.0 micrograms/dL. Abbott AxSYM was sensitive to T4 at a concentration of 0.34 microgram/dL. Linearity was excellent and consistent with the manufacturer's claim over a range 1.0 microgram/dL to 24 micrograms/dL. Of the interferents studied only hemoglobin caused a > 15% change in the measurement of T4.
  
  
  CONCLUSIONS
  The AxSYM immunoasssay analyzer performed to manufacturer's specifications and met HCFA allowable error limits for quantifying T4.
authors.affiliation: Department of Pathology & Laboratory Medicine, Medical School, University of Wisconsin, Madison 53792-2472, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Koch
authors.forename: F H
authors.initials: FH
authors.lastname: Wians
authors.forename: D
authors.initials: D
authors.lastname: Davis
authors.forename: D
authors.initials: D
authors.lastname: Burton
mesh_terms: D015982:Bias; D001774:Blood Chemical Analysis / Q000295:instrumentation*; D014487:Centers for Medicare and Medicaid Services, U.S.; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013974:Thyroxine / Q000097:blood*; D014481:United States