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

This study was to ascertain the reliability of sweat-testing by the Macrodu ct collection method combined with conductivity analysis (MCS) compared wit h the Gibson and Cooke technique (GCT). Sweat stimulation by pilocarpine io ntophoresis 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(R) c ollector on the other. Chloride, sodium and potassium concentrations were c hemically analysed both on paper-eluted and tube-collected sweat; the latte r was also analysed using a conductivity analyser. Chemical analyses were c ompared with conductivity analyses. This prospective study was carried out on 318 subjects with MCS (118 CFs, 200 controls) and on 305 of them with th e GCT (113 CFs, 192 controls). The pilocarpine iontophoresis produced adequ ate sweat in 96.4% of collections with GCT and in 90.9% with the MCS. Sensi tivity and specificity of the Macroduct(R)/conductivity system were compara ble to the GCT. No patient detected by the GCT technique was considered neg ative 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 b orderline range with the MCS. Conclusion: Sweat-testing by the MCS has acceptable sensitivity and specifi city when performed by trained CF sweat-testing technicians. Additional stu dies will be required to find out if these results can be confirmed in smal l clinics and hospitals where testing is done infrequently. Wherever the MC S is used all positive or borderline results should be confirmed by the CCT at a reference Cystic Fibrosis Center.