title: A solution for distinguishing Le(a-b-) sera in CA19-9 assays using SphereLight 180 and Architect i2000 assays.
abstract: BACKGROUND
  Measurement of carbohydrate antigen (CA) 19-9 is not applicable in patients with Lewis (Le) blood type, Le(a-b-). It is important to distinguish cases with Le(a-b-) before CA19-9 measurement. Therefore, we prepared a cut-off solution that gives a clear index to distinguish Le(a-b-) sera.
  
  
  METHODS
  The frequencies of Le blood types and the distribution of the CA19-9 values in each Le blood type were examined in 188 healthy subjects. The CA19-9 values for all Le(a-b-) sera and for a portion of Le(a-b+) sera exist below the limit of quantitation as measured by the SphereLight 180 kit. The cut-off solution, which gives a clear cut-off index (COI), was prepared to differentiate Le(a-b-) from Le(a-b+), and was evaluated using the SphereLight 180, Architect i2000, UniCel DxI 800, Elecsys 2010, and Lumipuls ƒ kits.
  
  
  RESULTS
  The COI was calculated as the mean +3 SD of the CA19-9 values of a cut-off solution that is adjusted to the limit of detection. Both the sensitivities and specificities of the COIs were 100% using the SphereLight 180 kit and 100% and 91.7%, respectively, using the Architect i2000 kit, but these values were not satisfactory using the other CA19-9 assay kits.
  
  
  CONCLUSIONS
  The COIs, determined by the cut-off solution, correctly identified all Le(a-b-) sera as Le(a-b-) and differentiated Le(a-b-) sera from other types of sera in CA19-9 assays using only the SphereLight 180 and Architect i2000 kits.
authors.affiliation: Division of Laboratory for Clinical Investigation, Department of Medical Technology, Osaka University Hospital, Suita, Osaka, Japan. hanada@hp-lab.med.osaka-u.ac.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hanada
authors.forename: Satomi
authors.initials: S
authors.lastname: Mugii
authors.forename: Keiko
authors.initials: K
authors.lastname: Takeoka
authors.forename: Ikuhiro
authors.initials: I
authors.lastname: Maeda
authors.forename: Mikio
authors.initials: M
authors.lastname: Watanabe
authors.forename: Yoh
authors.initials: Y
authors.lastname: Hidaka
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Iwatani
mesh_terms: D018395:CA-19-9 Antigen / Q000097:blood*; D006801:Humans; D007983:Lewis Blood Group Antigens; D057230:Limit of Detection
chemical_list: D018395:CA-19-9 Antigen; D007983:Lewis Blood Group Antigens