Sweat test results in children with primary protein energy malnutrition.

Abstract

We read with interest the recent article by Yigit et al. “Sweat Test Results in Children With Primary Protein Energy Malnutrition” (J Pediatr Gastroenterol Nutr 2003;37:242–5). The authors review found that it is difficult to exclude the diagnosis of cystic fibrosis (CF) in malnourished children because both primary protein energy malnutrition (PEM) and CF share similar symptoms, signs, and laboratory findings, such as elevated sweat chloride. Sweat tests were performed using the Macroduct® conductivity system (1). We published in the Journal of Pediatric Gastroenterology and Nutrition (1990;10:416–7) a letter to the editor entitled “The Sweat Crystallization Test in the Diagnosis of Cystic Fibrosis.” We also presented at the ECF meeting held in Praha [Acta Univ Carol Med Praha 1990;36(1–4):89–92], and published in An Esp Pediatr (1990;32:489–91) our 20-year experience with sweat crystallization test, first described by Kopito et al. (2). In an attempt to diminish the number of false-positive and false-negative results, especially in patients with malnutrition or respiratory allergy, we always use three methods to assess sweat: conductivity (Advanced Instruments® and Macroduct Wescor systems); quantitative measurement of sodium, chloride and potassium (Radiometer 100EML); and sweat crystallization. Sweat crystallization is a simple and inexpensive technique. Once you have the sweat with the Macroduct Collector you simply put a drop on a slide and warm it for 5 minutes. Then the heated sample is examined with a microscope. In patients with CF, you will see dendritic crystal forms, whereas in patients without CF, you will not (2,3). We have seen patients with CF (confirmed by genetics study) with normal sweat NaCl concentration and dendritic forms in sweat. In patients with asthma who had borderline or elevated results in sweat test, but not dendritic crystal forms, genetics study was negative for the most common CF mutations in our area, and quantitative sweat test results became normal later. We have also seen malnourished patients with positive conductivity sweat test results that became normal when they became well nourished. As Yigit et al. noted, borderline values on the sweat test are seen in as many as 20% of children with third-degree malnutrition. That degree of malnutrition is not so prevalent in our country. However, we think the sweat crystallization test may help clinicians everywhere to exclude the diagnosis of CF in situations where results of standard tests might be equivocal (4,5).