THE CF QUANTUM SWEAT TEST: NOT READY FOR CLINICAL USE

Abstract

The CF Quantum Test (CFQT) showed promise in a previous pilot study, however there was greater imprecision in one patch lot. Following the pilot study, the manufacturer changed their fabricating procedures. Subjects with previously diagnosed CF or subjects who required a sweat test for clinical reasons were invited to undergo the CFQT research test and a conventional sweat test (Macroduct®; collection and chloride analysis via the ChloroChek®; chloridometer). Previously diagnosed CF (n= 41) and CRMS (CFTR-related metabolic syndrome)/CFSPID (cystic fibrosis screen positive inconclusive diagnosis) (n= 3) patients and patients who required a sweat test for clinical indications (n=22) were recruited to have bilateral CFQT along with the Macroduct®; test performed on the same day. Pairs of data from each test were plotted as a correlation graph, bias plot and Bland Altman plot. Coefficient of variation (CV) between extremities and QNS rates for both tests were calculated. The CV between left and right extremities was greater in the CFQT (9.5%) compared to the Macroduct®; (4.8%). The QNS (quantity not sufficient) rates of the two tests were comparable (CFQT: 6.8%; Macroduct®;: 6.0%). There was greater imprecision with the CFQT results. The diagnostic agreement between the two tests was 100% positive percent agreement (95% CI: 90–100%), 100% negative percent agreement (95% CI: 80–100%), 67% intermediate percent agreement (95% CI: 30%–80%), and 92% overall percent agreement (95% CI: 80–100%). This follow-up study demonstrated that the CFQT is not analytically nor diagnostically reliable. (Clinicaltrials.gov identifier NCT01345617)