Evaluation of the AxSYM monoclonal cyclosporin assay and comparison with radioimmunoassay.

Recently, a semiautomated fluorescence polarization immunoassay (FPIA) for determination of parent cyclosporin (CsA) has been developed for the Abbott AxSYM system. The new CsA assay measures the drug from an extracted whole blood specimen. The authors report here the evaluation of this new assay and the comparison with a previously validated radioimmunoassay (RIA) method (CYCLO-Trac SP). To assess the imprecision, the authors used tri-level controls supplied by both Abbott and Bio-Rad manufacturers. The within-run CV ranged from 4.4% to 7.3% and the between-day CV ranged from 4.4% to 7.6%. Mean recovery of the drug from clinical specimens spiked with kit calibrators was 108.4%. Fluorescence polarization immunoassay AxSYM (y) was correlated to RIA (x) by using 132 trough blood specimens (44 renal, 44 liver, and 44 heart) from transplant recipients and resulted in the following Passing-Bablok linear regression equation: y = 6.7 + 0.97x, r = 0.989, S(x/y) = 12.9. The percentage of overestimation (mean, range) by FPIA AxSYM versus RIA was (3.8%, range -17.7% to 39.1%). The results observed with this new method from follow-up studies in patients during the early course after transplant were not consistently higher than those obtained by RIA. These findings contrast with previously reported results that compared FPIA TDx assay with RIA. The authors conclude that FPIA AxSYM is a precise method for measuring CsA and offers results similar to those obtained by RIA with a marked reduction in assay time.

Evaluation of circulating type I procollagen propeptides in patients with Paget's disease of bone.

We evaluated circulating aminoterminal and carboxyterminal propeptides of type I procollagen and total alkaline phosphatase levels in eighty consecutive patients affected by Paget's disease of bone. We compared the biochemical data with the extent of bone disease calculated on the basis of the bone scintigraphic indices. Serum aminoterminal propeptide of type I procollagen levels were high in 77% of patients, serum carboxyterminal propeptide of type I procollagen levels in 22% and serum total alkaline phosphatase levels in 76%. We found significant correlations between the three markers studied. The three biochemical markers correlated significantly with the bone scintigraphic activity indices, but the highest correlation coefficient was between the aminoterminal propeptide and total alkaline phosphatase. We conclude that there is a discrepancy between serum levels of the propeptides studied in relation to Paget's disease of bone. The sensitivity of the carboxyterminal propeptide of type I procollagen in this disease is low. In contrast the aminoterminal propeptide may be as sensitive a marker for the evaluation of this disorder as total alkaline phosphatase, and in addition may be more specific.