The sweat test, a clinical standard for diagnosing cystic fibrosis (CF), was found to be equally reliable for diagnosing CF in Down syndrome patients, according to a study published in the journal BMC Pulmonary Medicine.
Previous case reports have suggested an association between CF and Down syndrome. Although rare, the coexistence of these two diseases has been linked to a very poor outcome. Early detection of CF is crucial for timely and adequate care, especially for Down syndrome patients, who are susceptible to airway infections.
The test measures chloride levels in sweat, which are elevated in CF patients due to impaired activity of the CFTR protein. Previous studies have questioned its use in patients with Down syndrome, who have been seen to have changes in sweat gland anatomy. Changes in sweat composition also were reported in Down syndrome patients without signs of CF.
In this study, titled “Is sweat testing for cystic fibrosis feasible in patients with down syndrome?”, a research team at the Children’s Hospital of the University of Würzburg, in Germany, evaluated the validity of the sweat test in children with Down syndrome.
The study included 16 patients with Down syndrome and 16 healthy volunteers, ages 3 to 32. None of the participants showed clinical symptoms of CF, and no genetic testing was performed.
Examining chloride concentration in sweat test samples revealed that the Down syndrome group had a mean value of 15.54 mmol/L and the control group had 18.31 mmol/L. These values were clearly below the 60 mmol/L threshold that is used for CF diagnosis.
No association between chloride levels and gender were found in both groups. The researchers did find that chloride levels increased with age, but this progressive pattern was similar in both groups.
After evaluating the sweat secretion rate, the team found that Down syndrome patients produced significantly less sweat than healthy volunteers, and this was even more pronounced in women than in men.
Additionally, the sweat secretion rate increased with age in healthy volunteers, but not in the Down syndrome group.
“The different anatomy of sweat glands in DS [Down syndrome], as mentioned before, could be a reason for this difference,” researchers wrote.
“Our data suggests that analyzing sweat chloride concentration is a reliable tool to rule out CF in patients with DS, as we did not find any false positive results in our study population,” they added.
Because this study included a small number of participants, additional analysis is needed in larger cohorts of patients to further validate the findings, the team acknowledged.