The CF Quantum Sweat Test: Not Ready for Clinical Use

Abstract

ABSTRACT

The cystic fibrosis (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. Participants with previously diagnosed CF or participants 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 CF transmembrane regulator–related metabolic syndrome/CF 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 quantity-not-sufficient (QNS) rates for both tests were calculated. The CV between left and right extremities was greater in the CFQT (9.5%) compared with the Macroduct (4.8%). The QNS 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% confidence interval [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).