Sweat chloride measurement using direct potentiometry: Spotchem® (Elitech-Arkray) evaluation and comparison with coulometry and conductivity

Abstract

Sweat chloride (Cl(-)) measurement is a key step for the diagnosis of cystic fibrosis. The coulometric technique is validated in this context by international guidelines. The aim of our study was to evaluate the assay for sweat Cl(-) ions using direct potentiometry on disposable cassette (Spotchem™ SE EL-1520, Elitech-Arkray) by comparing results to those obtained on the same sample, by coulometry (Chloride analyser Sherwood 926S, Dutscher). To complete our table of correspondence between the results of Cl(-) ions and sweat conductivity (Sweat Check™ 3100), conductivity has been also achieved for 99 of the 139 sweat samples studied. Linearity of each technique performed extends from 10 to 120mmol/L. The coefficients of variation within and between runs are <5%. Comparison of 139 results (Passing - Bablock regression) shows a significant difference (p <0.001): [Spotchem] =1.026 [Chloride analyser] + 1.8, r =0.996. After correction with regression factors, only 6 pairs of values (4.6%) had a difference greater than ±5 mmol/L). The results of conductivity measurement is strongly correlated with those of Cl(-) ions (r =0.959 for Chloride analyser and 0.965 for Spotchem; p =0.576) with a linear relationship between the decision thresholds from 30 to 60mmol/L Cl(-). Sweat Cl(-) determinations using Spotchem™ analyser meet the criteria required by analytical recommendations. The technique is standardized, easy to perform and fast. Its good practicability makes the sweat test independent to operator and allows point-of care use.