Sweat Test
 Clinical significance:
 It’s a test used for diagnosis of a disease called Cystic Fibrosis.
 A sweat test measures the amount of salt chemicals (sodium and
chloride) in sweat. Sodium and chloride are part of your body’s
electrolyte balance, and combine to form the salt found in sweat. They
help regulate the fluid balance in your tissues. It is done to help
diagnose cystic fibrosis.
 Normally, sweat on the skin surface contains very little sodium and
chloride. People with cystic fibrosis (CF) have 2 to 5 times the normal
amount of sodium and chloride in their sweat.

Cystic fibrosis:
Cystic fibrosis (CF), mucoviscoidosis, or mucoviscidosis, is a lifethreatening hereditary disease which is inherited as autosomal recessive
and is characterized by:
1. Increased viscosity of mucous secretions, including those of (pancreas,
intestinal glands, tracheal, peritracheal, bronchial).
 Thick mucus production, as well as a less competent immune system,
cause mucus to build up and clog some of the organs in the body,
particularly in the lungs and pancreas. When mucus clogs the lungs, it
can make breathing very difficult. The thick mucus also causes bacteria
(or germs) to get stuck in the airways, which causes inflammation (or
swelling) and infections that leads to lung damage.
 Mucus also can block the digestive tract and pancreas. The mucus stops
digestive enzymes from getting to the intestines. The body needs these
enzymes to break down food, which provides important nutrients to
help us grow and stay healthy.
2. Increased concentration of electrolytes especially Na and CL, in
secretion of other gland notably (sweat glands, Parotid salivary glands,
lachrymal glands).
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 Symptoms of cystic fibrosis (CF)
 Thick, viscous mucus secretions in the lungs.
 Repeated infections: The accumulation of sticky, thick mucus in the
lungs creates a favorable environment for infectious microorganisms
to inhabit and flourish.
 Stools that are pale or clay colored, foul smelling, have mucus.
 Recurrent pneumonia
 Chronic cough, possibly with blood streaking
 Wheezing
 Bronchitis
 Chronic sinusitis
 Asthma
 Weight loss, failure to thrive in infants, abdominal swelling
 Excessive salt in sweat, dehydration
 Failure of newborn to pass stool (constipation)
 Abdominal pain, flatulence
 Fatigue
 Changes in color and amount of sputum (material coughed up from
the lungs).
 Sweat analysis:
Two methods of sweat analysis are most frequently used: chloride
concentration and conductivity measurement. Sweat chloride test is the
standard diagnostic test for CF. A high salt level in the patient's sweat is a
sign of the disease. Sweat conductivity may be used to screen for CF.
 Principle:
Measurement of the concentration of Chloride in sweat throughout A
device called (Iontophoresis) which consists of two electrodes , positive &
negative , so chloride which has a negative charge directs into the positive
electrode & generate pulses , the increase of this is proportional to
concentration of chloride in sweat.
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First Step - Stimulating Sweat: The technician will place two electrodes
containing a sweat-inducing drug called pilocarpine on the skin. A small
electric current is delivered through the electrodes to help the pilocarpine
stimulate sweat. The current is not painful, but a slight tingling sensation
may be felt.
Second Step – Collecting Sweat: After about 10 minutes, the technician
stops the current and removes the electrodes. The skin is wiped dry and a
piece of filter paper covered with plastic, sometimes called a “sweat patch”
is placed on the site to collect the sweat. When a sufficient amount of
sweat is collected, usually about 30 to 45 minutes, the sweat-drenched
paper is removed and sent to the lab for testing.
Equipments:
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buttery with two electrodes (+ve & -ve)
Supply kit which contains : Gel ,watch, cuvette
Cotton & Alcohol
Distilled water
Sticks
Syringe for push fluid into cuvette
 Procedure:
The sweat test is usually done on the forearm, but may be done on the
thigh of infants and children with small arms.
1- The patient (Child) came to the lab with his/her mother .
2-We receive the request of sweat test .
3-Clean an arm of the child with cotton & Alcohol , repeated it many times to make a
clean arm without any dirty.
4- After that, we clean the arm with distilled water for many times to ensure that there
is no alcohol on the arm.
5- We put Positive Anode (+ve) of the buttery ( Red color) on the lower of child arm,
the Negative Cathode(-ve) above the anode, with its gel for each one. Then we fix it
with Sticks & power on the buttery & wait 3 minutes or until the current stop from
the buttery (We know that through sound issued by the device).
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6-Remove the anode & cathode from the child arm, & wet the
area of the arm by cotton & Distilled water.
7-We put the sweat collection watch on the same area that we put
the a node electrode , & fix it with sticks.
8- We tell the mother to return after 30 minutes with warming
the child to let hem sweating & to stimulate the sweat gland to secrete sweat.
9-After 30 min. we remove the watch & suck the blue fluid (Chloride) by needle to
cuvette. Then entered it by a pipette to the small cuvette of the device.
10- The sweat test usually takes 45 minutes to 1 hour.
11-Then we measure CL by automated or manual titration method and Na by flame
photometry or ion exchange electrode.
 Results:
A sweat test measures the amount of salt chemicals (sodium and chloride)
in sweat. Generally, chloride (sweat chloride) is measured.
 Sweat chloride:
 Normal Less than 40 mill moles per liter (mmol/L).
 Borderline (suspect) 40–60 mmol/L.
 Abnormal More than 60 mmol/L.
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