Annals of Clinical Biochemistry > Volume 45, Number 6 > Pp. 535-538

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Mackay, R J Articles by Woods, S Search for Related Content PubMed PubMed Citation Social Bookmarking                      What's this?

Personal View

Uncertainty of sweat chloride testing: does the right hand know what the left hand is doing?

R J Mackay, C M Florkowski, P M George, C W Sies and S Woods

Biochemistry Unit, Canterbury Health Laboratories, PO Box 151, Christchurch 8011, New Zealand

Corresponding author: Dr R J Mackay. Email: richard.mackay{at}cdhb.govt.nz

Although analytical variation in sweat electrolyte testing can be easily estimated, there is limited data on total variation. This study aims to evaluate the total variation of the sweat test by measuring the difference between sweat electrolyte values in specimens obtained simultaneously from two sites. Chloride is recommended in published guidelines as the only discriminant for the diagnosis of cystic fibrosis, and sodium may be measured as a guide to the adequacy of collection and analysis. Both are reported here. Sweat was collected in patients by the Gibson Cooke method from two sites simultaneously. Coefficient of variation in this laboratory is 4.1 and 5% for chloride and sodium, respectively. 295 patients had sufficient sweat collected from both sites for analysis. The values for chloride and sodium were compared between the two sites. The total coefficient of variation (CV_t) calculated for the whole group between the two sites was 20.2% for chloride and 16.9% for sodium, and the standard deviations 4.3 mmol/L and 4.8 mmol/L, respectively. In patients with intermediate chloride concentrations; in different age groups; and when those tests with a difference between sodium and chloride concentration of more than 15 were excluded, minimal differences in these figures were observed. Use of strictly defined cut-off points to discriminate between normal and intermediate electrolyte values, and between intermediate and raised electrolyte values, does not reflect the variation in sweat electrolyte content found within an individual patient. This has important implications for reporting.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?