Reliability of sweat-testing by the Macroduct collection method combined with conductivity analysis in comparison with the classic Gibson and Cooke technique

Abstract

This study was to ascertain the reliability of sweat-testing by the Macroduct collection method combined with conductivity analysis (MCS) compared with the Gibson and Cooke technique (GCT). Sweat stimulation by pilocarpine iontophoresis was identical for both procedures, sweat being collected for 30 min on a filter paper on one forearm and in the coil of the Macroduct collector on the other. Chloride, sodium and potassium concentrations were chemically analysed both on paper-eluted and tube-collected sweat; the latter was also analysed using a conductivity analyser. Chemical analyses were compared with conductivity analyses. This prospective study was carried out on 318 subjects with MCS (118 CFs, 200 controls) and on 305 of them with the GCT (113 CFs, 192 controls). The pilocarpine iontophoresis produced adequate sweat in 96.4% of collections with GCT and in 90.9% with the MCS. Sensitivity and specificity of the Macroduct/conductivity system were comparable to the GCT. No patient detected by the GCT technique was considered negative by conductivity, but one GCT positive was "borderline" with the MCS. Six non-CF subjects identified as negative by the GCT (3.3%) were in the borderline range with the MCS.

Conclusion: Sweat-testing by the MCS has acceptable sensitivity and specificity when performed by trained CF sweat-testing technicians. Additional studies will be required to find out if these results can be confirmed in small clinics and hospitals where testing is done infrequently. Wherever the MCS is used all positive or borderline results should be confirmed by the GCT at a reference Cystic Fibrosis Center.