title: Modified pentamer formation assay for measurement of tacrolimus and its active metabolites: comparison with liquid chromatography-tandem mass spectrometry and microparticle enzyme-linked immunoassay (MEIA-II).
abstract: A modified pentamer formation assay (PFA) for quantification of tacrolimus and active metabolites after extraction from whole blood is described. The lower limit of detection was 2 microg/L. Intraassay precision (CV) was 5.7-13.7%, and the interassay CV was 6. 1-14.9%. Tacrolimus trough concentrations in 104 whole blood specimens from liver and kidney transplant recipients were compared with results from HPLC-tandem mass spectrometry (LC/MS/MS) and microparticle enzyme immunoassay (MEIA-II). Data were analyzed by difference plots and are presented as median (95% confidence intervals) of the method differences. MEIA-II results were on average 2.00 microg/L (range, -0.08 to 5.17 microg/L) higher than LC/MS/MS, whereas PFA results were only 1.07 microg/L (range, -2.62 to 5.33 microg/L) higher. Of 104 specimens tested, 25 displayed differences >/=3 microg/L between MEIA-II and PFA: median difference, 4.65 microg/L (range, 3.01-8.79 microg/L). The corresponding median difference between PFA and LC/MS/MS was -0.91 microg/L (range, -4.11 to 0.85 microg/L), and the difference between MEIA-II and LC/MS/MS was 3.67 microg/L (range, 1.88-6.34 microg/L), suggesting the presence of inactive metabolites that caused a positive bias in the immunoassay. In contrast, similar median differences were observed for the remaining 79 specimens: MEIA-II minus LC/MS/MS, 1.78 microg/L (range, -0.45 to 4.11 microg/L); PFA minus LC/MS/MS, 1.90 microg/L (range, -1.70 to 5.50 microg/L). Active tacrolimus metabolites may have contributed to the higher apparent tacrolimus concentrations in these specimens.
authors.affiliation: 1 Abteilung Klinische Chemie, Georg-August-Universitaet Goettingen, D-37075 Goettingen, Germany. varmstro@med.uni-goettingen.de
authors.forename: V W
authors.initials: VW
authors.lastname: Armstrong
authors.forename: E
authors.initials: E
authors.lastname: Schuetz
authors.forename: Q
authors.initials: Q
authors.lastname: Zhang
authors.forename: S
authors.initials: S
authors.lastname: Groothuisen
authors.forename: C
authors.initials: C
authors.lastname: Scholz
authors.forename: M
authors.initials: M
authors.lastname: Shipkova
authors.forename: H
authors.initials: H
authors.lastname: Aboleneen
authors.forename: M
authors.initials: M
authors.lastname: Oellerich
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007166:Immunosuppressive Agents / Q000097:blood* / Q000737:chemistry / Q000627:therapeutic use; D016030:Kidney Transplantation; D016031:Liver Transplantation; D012044:Regression Analysis; D016559:Tacrolimus / Q000097:blood* / Q000737:chemistry / Q000627:therapeutic use
chemical_list: D007166:Immunosuppressive Agents; D016559:Tacrolimus