Lack of specificity of cyclosporine immunoassays. Results of a College of American Pathologists Study.
OBJECTIVE
To evaluate the cross-reactivity of the 6 most abundant cyclosporine A (CsA) metabolites in commonly used assays for CsA.


METHODS
Whole blood samples containing either only 62 ng/mL CsA (A) or 62 ng/mL CsA and between 49 and 86 ng/mL of 1 of the 6 most abundant CsA metabolites (B) were lyophilized. One sample of A and 1 of B were mailed to each of the laboratories participating in the College of American Pathologists Proficiency Testing Program quarterly during a 3-year period (1999-2001). Method means and coefficients of variation were calculated for each mailing.


RESULTS
The study showed significant cross-reactivity of metabolites in all the immunoassay systems studied. Overall degree of interference decreased from Abbott TDx polyclonal > Abbott TDx monoclonal > DiaSorin > Syva EMIT. High-performance liquid chromatography methods gave results close to those found using mass spectrometric techniques.


CONCLUSIONS
Significant metabolite interference was found to occur with the immunoassay systems studied.
Soldin
Steven J
SJ
Department of Pathology, the George Washington University School of Medicine, Children's National Medical Center, Washington, DC 20010, USA. ssoldin@cnmc.org
Steele
Bernard W
BW
Witte
David L
DL
Wang
Edward
E
Elin
Ronald J
RJ
D002851:Chromatography, High Pressure Liquid; D003429:Cross Reactions; D016572:Cyclosporine / Q000097:blood / Q000276:immunology* / Q000378:metabolism; D007118:Immunoassay; D007753:Laboratories / Q000592:standards; D007959:Lymphocyte Culture Test, Mixed; D010336:Pathology / Q000592:standards; D012680:Sensitivity and Specificity
D016572:Cyclosporine