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This is a test to measure the chloride content in the sweat. The test result helps diagnose Cystic Fibrosis (CF). CF is an inherited disease that makes patients sick by disrupting the normal function of epithelial cells. These cells are present in the sweat glands in the skin, breathing tubes inside the lungs, liver, pancreas, and digestive and reproductive systems. Patients with CF are at risk for repeated lung infections.
Typically, patients with CF have higher concentration of chloride in their sweat. In a sweat test, the skin is stimulated to produce enough sweat needed for analysis.
Why we do this test? Doctors may order a sweat test for infants with a positive newborn screening for Cystic Fibrosis or for children with a family history of Cystic Fibrosis, or symptoms of the disorder. Symptoms and signs include poor weight gain, repeated lung infections and digestive problems. The test can be done as early as 48 hours after birth, though any test done during a baby's first month might need to be repeated because newborns may not produce enough sweat to ensure reliable results.
Preparation No special preparation is necessary for this test. Before having this test, your child may eat, drink, and exercise as usual, and continue to take any current medicines. Creams and lotions should not be applied to the skin (on both arms) for 24 hours before the procedure. A sweat test usually takes about an hour, so you may want to bring books or toys to help your child pass the time. There are no needles used in this procedure.
Procedure An area of skin on the arm will be cleaned and dried. Next, two electrodes with straps will be attached to the arm (Fig 1). The electrodes will contain a disc with pilocarpine gel, a medicine that makes the sweat glands produce sweat. A very weak electric current will be applied to push the medicine through the skin. Following this, the electrodes are removed and the skin is cleansed.
A special sweat collection device is then attached to the clean skin surface in the area where the sweat glands were stimulated (Fig 2). It is secured to the skin to keep it from moving. The sweat is collected for 30 minutes. The sweat collected will turn blue when it comes into contact with the blue dye within the collector, making it visible to the technician. After enough sweat is in the tubing inside the collector, the sweat collector will be removed and the sweat will be placed in a tube for analysis. The arm will be cleaned again.Fig 1: Two electrodes with straps attached to the forearm.Fig 2: Sweat Collector device attached to the skin.
Results Results are usually available in one to two days. If your child has a sweat chloride level of more than 60 millimoles per liter, it is considered abnormal and indicates a high likelihood of Cystic Fibrosis, though some children with CF do have borderline or even normal sweat chloride levels. If the result is inconclusive or if the sweat collected is insufficient for analysis, the test may need to be repeated. If results are positive or unclear, a blood test (genetic test) may be needed.
Risks This test poses very little risk of complications. This test shouldn't be painful, though some kids do feel a slight tingling or tickling sensation when the electrodes apply current to the skin. The electric current may cause your child's skin to be red or to sweat excessively for a short period of time. Most people exhibit sensitivity to pilocarpine that is typically manifested as mild redness of the skin where electrodes were placed. This usually resolves spontaneously within a short period of time. Occasionally one or more blister-like reaction may occur, which usually disappear within two to three hours. In rare cases (less than one in 50,000 tests), minor skin burns may occur in areas where the electrodes were applied.
Enquiries If you have questions about the scheduled sweat test, please contact the respiratory laboratory at 6394-2130.