07 June 2012

Bennett's Sweat Test

One of the most classic (and one of the oldest) tests to confirm the diagnosis of Cystic Fibrosis is the "Sweat Test."

This test, first created in the 1950's, measures the amount of sodium and chloride in a person's sweat. The higher the amount, the more likely someone may have Cystic Fibrosis.  (Notice Bennett's right arm.)

Bennett did not undergo this test at birth, like many do at the time of their diagnosis.  Instead, he was given a blood test/genetic test to confirm he has two genetic mutations for Cystic Fibrosis.  However, Brian and I decided we wanted to know Bennett's baseline sweat test scores as we are hopeful that Bennett will eventually have access to some of the new medications that are potentially coming down the pipeline.

Oliver watches carefully as the nurse prepares Bennett for the 45 minute test.

The sweat test reveals how much Cystic Fibrosis is "wreaking havoc" in the body.  For those who have mild CF, the test will reveal lower numbers than those who, like Bennett, have severe Cystic Fibrosis.

The sweat test is really interesting.  Because it's an older test, it's a bit intimidating to see.

The way the sweat test worked is the nurse washed and dried Bennett's skin on the inside of each arm.   Then, she placed two small gauze pads on the skin.

One pad was soaked in a medication called pilocarpine (which causes the skin to sweat).  The other is soaked in salt water.

Then, the nurse placed two small electrode pads over the gauze pads.

I thought the "example picture" on the instrument box were interesting.

These electrodes were hooked up to an instrument that produces a mild electric current which pushes the medicine into the skin.

Let's be honest, sorta creepy, if you ask me.

Just for the record, Bennett was none too happy.

We had to old Bennett's arm and wait during the test.

After 5 minutes, the nurse removed the gauze pads and electrodes and replaced them with a dry gauze pad to collect the sweat.  In Bennett's case, a fiberglass casting tape, was wrapped over these pads to provide fluid loss.

We waited for about 30 minutes on each arm for the sweat to collect.

The nurse wrote the time we had to return per arm.  Eleven fifty-one a.m. was our time to return on Bennett's right arm.

Thank goodness of the ipad.  It helped tremendously in distracting him the entire time the electrodes were going and for the 30 minute wait on each arm!

After the test, the nurse was able to remove the pads and place them in a sealed bottle.  It was weighed to measure how much sweat the skin produced.  Then, it was checked to find out how much sodium and/or chloride the sweat contained.

Bennett's arm was red and a bit swollen after the test but it went away about an hour later.

If Bennett's sweat chloride levels had come back less than 39mmol/L, it would have indicated that Cystic Fibrosis is very unlikely.  If Bennett's sweat chloride levels had come back between 40-59 mmol/L, it would have meant that Cystic Fibrosis is possible.  Any amount more than 60 mmol/L indicates Cystic Fibrosis is highly likely.  No surprise to us, when we got Bennett's test results back a few days later, they were 122 (left arm) and 114 (right arm).

Thankfully, Bennett recovered just fine from his test and is feeling much better now.  Now to try to get him on some medications that are going to save his life so we can begin to see these sweat test numbers go down!!


  1. Wow! How interesting to see the sweat test done on an older child! My son had his done at 32 days old and they couldn't get him to sweat at all. We actually only got one number and that was barely. (I think his number was 108, but let's be honest, those early days are all a blur.) I also think it's interesting that the test is done differently at different clinics. Our clinic collected the sweat differently and only had one electrode (with the sweat stimulant and not the saline one) on each arm. And there was no redness or swelling afterwards. Maybe because he was so little? Very interesting! Thanks for sharing.

  2. Wow, that's an old machine! Looks like B is enjoying Monkey Preschool lunchbox. It's a fav here too!

  3. Sara was tested 8 weeks old, she had a portable device attached to the sweat thingy on her arm for an hour or so. They never put any meds on her arm before. Her results came back 117 and was read instantly. Just had to wait about 5 minutes.

  4. Poor little guy! It about broke my heart to see him so unhappy! However, I loved the spiffy ipad case....that's awesome! I'm sorry the numbers were high - seems as if any time you see those as a stark reminder of the condition your child has, can be slightly disappointing. I know I always wish certain allergy numbers were lower when tested...and they never are. Anyway, Bennett was brave and I'm glad yall have this baseline number for him. I'm sure you will be glad you have that one day. Thanks for sharing!

  5. This post is very interesting because it shows, for the first time, how the sweat test looks like for the patients and parents.Benett looks not very happy, and I'm sure he is not the only one boy who cry during this experience. And yes, this old machine with those cables connected to the arms looks very intimidating. There is also a comment of other people who get the result instantly ( probably only conductivity was measured, not chloride). It would be interesting to know about more sweat test experiences !


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