I can't begin to figure how to make a 21 month old boy sweat. I'm pushing 65 and I still can't sweat on command. My non CF brother is five years my senior and a born athlete. When brother Bob was about 14, he converted a basement room into a gym. At first he lost weight and after a year or so, he began to slowly put on some real muscle. And he trained to sweat. He could sweat competitively if it were a sport. I would parrot his workout routine, usually following each routine with less weight. In the hour or so workout, Bob drank three to four quarts of water. I would sip away on a glass of water but I wasn't thirsty and it often gave me a stomach ache, but I could not sweat to save my life.
There have been CFers and CF caregivers that have repeated a sweat chloride test a dozen times, even two dozen times in rare cases. Unlike traditional tests, medical tests are variable. Why do so many CFers or potential CFers fail to produce enough sweat to analyze? If anybody searches this site for posts and threads about failed sweat tests, it seems like a very common issue.
Small Duct Disease (SDD), is a hallmark of CF. Typically, SDD affects our ducts like the common bile duct, pancreatic ducts, liver ducts and so forth. But every mucus gland is a miniature duct system. Like diagrams of our sweat glands, a long duct is coiled into a ball with blood capillaries feeding from below and the end erupting at the skin's surface in the form of a pore. About the only time WE worry about a sweat gland is when a big one get plugged right on the end of our nose.
As more of an indicator, unlike most kids, I loved naps and I loved baths and showers. I would think many if not most CFers feel this way. My mother used to chide me about the excess of "white heads" everywhere and "black heads" on my neck. The black heads of course bothered me and I found a syringe type of tool that would suck those babies clean. I was flat out astonished at how much gunk was behind the tiny bit of black that covered the pores. I'm not talking about age 13 or 18 but at 9 and 10 part of my daily toilet was devoted to mechanically cleaning my sweat glands. I did the same with pimples but that's another story.
We have two types of sweat glands under our skin. One type comes with a hair follicle and one does not. Apocrine sweat glands are concentrated around hairy parts of the body like the arm pits. These aren't the right kind of sweat glands for a sweat chloride test. Eccrine sweat glands are all over our bodies with concentrations at the hands and feet. Why they do a sweat test on the arm or leg and not our clammy hands and feet might have to do with the tiny electric current they run through the skin to stimulate sweat glands. Ouch! I honestly wonder why they don't test the palms or feet. My hands sweat so much salt, I must wipe my steering wheel down fairly regularly and to date I have not found a watch band that doesn't rot off my wrist including stainless steel.
I was a scientist even as a kid and my curiosity over what was clogging my pores became an experiment of sorts. Having a brother five years older gave me access to the methods of analyzing the contents of my plugged sweat glands. By reading up on what waste is excreted by sweat glands plus the expected contents of sweat when they are working properly, I narrowed my search to salts and toxins like urea and lactic acids. A plugged sweat gland is almost pure salt mixed in with water and traces of body wastes like lactic acid, which gives it an oily consistency.
Normal sweat is supposed to be close to our 0.9% saline. Really! When CFers sweat from exercise, the sweat that gets into our eyes burns like sin. The 6% salt solution in sea water doesn't burn our eyes so just how strong is that sweat? Once sweat gets flowing from a sweat gland and it isn't still cleaning out concentrated salts stored in the duct, it could be salty enough to peg the test. In order to sweat, we must be well hydrated which means water and plenty of electrolytes.
Although the test is specific to choride ions, our electrolyte balance is many salts like potassium chloride, calcium chloride and magnesium chloride. An imbalance in any one salt is enough to throw the chloride concentration off. Don't be discouraged by a non positive test. It is common to repeat this test until a positive result is made. It isn't as crazy as it sounds. Genetic testing can say for certain if your child has the potential for cystic fibrosis but it isn't able to determine how serious the issues are likely to be or become.
The amount of excess chloride in our sweat is a direct indicator of disease, in our case CF. So being tested and tested until a positive result is obtained has some reasoning in the apparent madness. It also could be an indicator of seriously small ducts, and small duct disorder, or disease. Our mucus glands, salivary glands, thyroid glands, breasts, pancreas and other endocrine glands all utilize mucus glands for a transport liquid. Our glands are loaded with mucus glands who's only function is to make liquids for transporting other chemicals such as enzymes or hormones or dust and pollen trapped by cilia often found around the mucus gland's pores. The fact that the sweat glands refuse to work could because they are clogged.
I finally trained my sweat glands to sweat. But like muscles, you need to exercise them. Sauna therapy is a controversial way to stimulate sweating. From infancy there was a local mineral hot springs that we all gathered at. Most times all I got for my efforts was a case of prickly heat, a rash from highly acidic plugged pores that failed to break open and flow with sweat. Prickly heat rash is when our eccrine pores plug up and Baking soda treatment would cake on my skin like some abrasive grit. But using that grit to exfoliate my skin had certain advantages. I'm not suggesting you send your baby for a skin peel but from the little research I can find on the subject, CFers don't easily sweat, nor do they sweat adequately.
Don't worry about a negative sweat test, especially one that is incomplete do to quantity. Worry about having any health issues addressed. Your son may never produce a passing sweat test, or it may be negative. A CF child may not even show CFTR genes, although we understand more about non-mutation mutations, or errors like T polymorphisms.
It seems ghoulish at times searching for a firm diagnosis but the frustration of being happily told what you or your child doesn't have instead of a diagnosis for what he does have is understandable. Someday I hope medicine finds a less judgmental term for tests.
LL
