As mentioned earlier, sweat tests are conducted on any person suspected of having cystic fibrosis. This could even be administered on a couple of days old infant. Although, tests conducted in infants may have to be repeated at a later date, as infants don't sweat enough to give accurate results. A sweat test may also be taken if there is a history of cystic fibrosis in the family.
The sweat test takes roughly about 45 minutes to an hour to complete. Here the doctor dabs sweat inducing medicine on a patch of the skin, more often on the arm or thigh. He then places a gauze pad over the medicine which will collect the sweat from that area. The chloride and sodium levels are then measured.
Unlike other tests this one needs no preparation. Typically blood and urine tests are taken first thing in the morning and on an empty stomach. But sweat tests need no such hassle. You can carry on with you daily activities. Indeed if you are taking some other medication, you can have that too, as none of these things have any bearing on the
Before administering the test, the patch of skin is washed and dried. After this, two gauze pads are placed on that patch. One pad contains sweat medicine called pilocarpine and the other one is wet with salt water. Above these another couple of pads are placed. These pads are referred to as electrodes and these are connected to an instrument that transmit electric current through the electrode down the gauze pads pushing the sweat medicine into the skin.
When this current is passed, most people usually get a ticklish sensation. However, if you experience a burning sensation, it means the pads haven't been place appropriately. The bottom line is that this is not a painful test, only a lengthy one.
After about ten minutes the electrode pads and gauze pads are removed and the skin is once again washed and dried. You will notice that the skin under the medicine gauze has become red. This is nothing to worry about. Now, on this skin, the doctor will place a dry gauze or paper pad or in some cases even a tube. Whatever the material, this is glued to the skin with plastic or wax to avoid loss of fluid (sweat evaporation). This pad/paper/tube is kept on the skin to soak up sweat for about a half hour after which is stored in a sealed bottle. Before the doctor measures the chloride and sodium content in the sweat, he will weigh the bottle to know how much sweat was collected.
The skin is for the third time washed and dried. However it is quite likely that the tested skin remains red and sweats for a few more hours. This is not a matter of concern as these effects will diminish overnight.
This is a simple test with very few risks, especially because it is always conducted only on the arm or thigh and never on the chest.
This eliminates the probability of an electric shock. In some cases, after the redness and sweating disappear the skin looks a little burnt, but there will definitely be no pain or soreness.
Bear in mind, a sweat test only indicates the presence of cystic fibrosis. It cannot determine how mild or intense the disease actually is.