Sweat Testing

 The sweat test is the simplest and most reliable method for diagnosing cystic fibrosis (CF). In CF, the sweat glands produce sweat that is much higher in salt content than normal. 

Physicians order this test on patients who have any of the following symptoms:

 

  • recurrent wheezing

  • persistent cough and excessive mucus

  • recurrent pneumonia

  • failure to gain weight, often despite a good appetite

  • abnormal bowel movements (often chronic diarrhea; stools are frequent, bulky, greasy, and foul-smelling)

  • salty tasting skin

  • nasal polyps (small fleshy growths inside the nose)

  • clubbing (enlargement) of the fingertips and toes

*None of these symptoms are unique to CF; they may appear in other illnesses. Also, a person with CF may not have all of these symptoms.

 

Contraindications:

If anyone has dermatitis, rashes, lesions, or peripheral edema the test should not be done until the condition has cleared up.

Ordering:

A written order form from a physician is needed. Call the Pediatric Pulmonary Laboratory 734-936-9515 to make an appointment for the sweat test. Tests are performed Monday through Friday 8AM through 4 PM. They are an hour in duration. There is no patient preparation.

Testing technique:

The sweat test is painless and is performed on the arm or back. The sweat glands are stimulated to sweat using a harmless chemical called pilocarpine, which is drawn into the skin by a very small amount of electricity (1.8 mAmps) from a battery box. (This technique is called pilocarpine iontophoresis.) After 15 minutes of stimulation the site is washed with deionized water and dried. A weighed piece of filter paper with a plastic cover is placed there to collect the sweat. Thirty minutes later the paper is removed and weighed for the amount of sweat. Minimum required amount for analysis is 75mg. After the paper has soaked 15 minutes with deionized water the solution is analyzed for the chloride level on a Buchler digital chloridometer. A high level of 60mEq/L or greater is consistent with the diagnosis of CF.

 

 

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