A chloride test measures the level of chloride
in your blood or urine. Chloride is one of the most important
electrolytes in the blood. It helps keep the amount of
fluid inside and outside of your cells in balance. It also helps maintain
proper blood volume, blood pressure, and
pH of your body fluids. Tests for sodium, potassium,
and bicarbonate are usually done at the same time as a blood test for
Most of the chloride in your body comes from the salt
(sodium chloride) you eat. Chloride is absorbed by your
intestines when you digest food. Extra chloride leaves
your body in your urine.
Sometimes a test for chloride can be done
on a sample of all your urine collected over a 24-hour period (called a 24-hour
urine sample) to find out how much chloride is leaving your body in your
Chloride can also be measured in skin sweat to test for
Why It Is Done
A test for chloride may be done
- Check your chloride level if you are having
symptoms such as muscle twitching or spasms, breathing problems, weakness, or
- Find out whether you have
adrenal gland problems.
- Help find the
cause for high blood pH. A condition called metabolic alkalosis can be caused
by a loss of acid from your body (for example, from a loss of electrolytes
through prolonged vomiting or diarrhea). You may also have metabolic alkalosis
if your body loses too much sodium or you eat too much baking soda (sodium
How To Prepare
You do not need to do anything before
you have this test.
Tell your doctor if you:
Talk to your doctor about any concerns you have regarding
the need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional taking a sample
of your blood will:
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
- You start collecting your urine in the
morning. When you first get up, empty your bladder but do not save this urine.
Write down the time that you urinated to mark the beginning of your 24-hour
- For the next 24 hours, collect all your urine.
Your doctor or lab will usually provide you with a large container that holds
about 1 gal (4 L). The
container has a small amount of preservative in it. Urinate into a small, clean
container and then pour the urine into the large container. Do not touch the
inside of the container with your fingers.
- Keep the large container
in the refrigerator for the 24 hours.
- Empty your bladder for the
final time at or just before the end of the 24-hour period. Add this urine to
the large container and record the time.
- Do not get toilet paper,
pubic hair, stool (feces), menstrual blood, or other foreign matter in the
The skin sweat test for chloride is primarily used to
test for cystic fibrosis. For more information, see the medical test