Elsevier

The Journal of Pediatrics

Volume 153, Issue 6, December 2008, Pages 758-763.e1
The Journal of Pediatrics

Original article
Diagnosis of Cystic Fibrosis by Sweat Testing: Age-Specific Reference Intervals

https://doi.org/10.1016/j.jpeds.2008.04.067Get rights and content

Objective

To develop reference intervals (RIs) for sweat chloride and sodium in healthy children, adolescents, and adults.

Study design

Healthy, unrelated subjects aged from 5 to >50 years and subjects who were pancreatic insufficient with cystic fibrosis (CF) were recruited. Sweat collection was performed on all subjects with the Wescor Macroduct system. Sweat electrolytes were analyzed with direct ion selective electrodes. ΔF508 mutation analysis was performed on the healthy subjects ≥15 years old.

Results

A total of 282 healthy and 40 subjects with CF were included for analysis. There was no overlap of sweat chloride between the group with CF and the group without CF, but there was some overlap of sweat sodium. Sweat chloride increased with age, with the rate of increase slowing progressively to zero after the age of 19 years. The estimated median (95% RI) for sweat chloride were: 5 to 9 years, 13 mmol/L (1-39 mmol/L); 10 to 14 years, 18mmol/L (3-47 mmol/L); 15 to 19 years, 20 mmol/L (3-51mmol/L); and 20+ years 23 mmol/L (5-56mmol/L).

Conclusions

We have successfully developed the age-related RI for sweat electrolytes, which will be useful for clinicians interpreting sweat test results from children, adolescents, and adults.

Section snippets

Subjects

We recruited subjects with CF and control subjects for the study during the period February 1, 2005, to November 1, 2006.

Control Subjects

Participants were recruited through advertisements at The Royal Children's Hospital and from a local school. Participants without CF were screened with a purpose-designed health questionnaire to exclude a CF phenotype (respiratory diseases, gastrointestinal symptoms, heat stroke, and male infertility), family history of CF, and diseases known to affect sweat electrolyte

Subjects' Selection

A total of 340 participants were recruited (Figure 1; available at www.jpeds.com).

Control Subjects

There were 300 participants without CF aged 5 to 68 years. Three subjects were excluded because of a family history of CF, and 9 subjects were found to be ΔF508 carriers. Of the remaining 288 subjects, 11 had insufficient sweat on the first occasion, and for 2 subjects the analysis was not possible because of technical error. All of these subjects were asked for a repeat sweat test. Six subjects were excluded

Discussion

In this study, age-related RIs have been developed for sweat chloride and sodium concentrations from unrelated participants (5-68 years old) with no family history of CF, no conditions known to affect sweat chloride and sodium concentrations, and who were not ΔF508 carriers. The sweat stimulation, collection, and analysis was performed as recommended by using international guidelines.11, 12, 13 No overlap in sweat chloride concentrations was observed between the group with CF and the group

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    Supported by a Scientific Grant from the Australasian Association of Clinical Biochemists. The authors declare no conflicts of interest.

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