How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
There is very little chance of a
problem from having blood sample taken from a vein.
- You may get a small bruise at the site. You
can lower the chance of bruising by keeping pressure on the site for several
- In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding
disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can
make bleeding more likely. If you have bleeding or clotting problems, or if you
take blood-thinning medicine, tell your doctor before your blood sample is
A chemistry screen is a blood test that
measures the levels of several substances in the blood (such as
Normal values vary from
lab to lab and depend on which tests were included in your chemistry screen.
Results are usually available in 1 to 2 days.
Many conditions can
change chemistry screen test levels. Your doctor will talk with you about any
abnormal results that may be related to your symptoms and medical history. For
more information about normal and abnormal values, see:
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
- Taking medicine. Some medicines can cause
changes in the normal values of a chemistry screen.
- Eating high-fat
foods or drinking alcohol.
intravenous (IV) fluids, such as fluids given during
What To Think About
There are several different
chemistry screens. For example, an SMA-7 looks at 7 substances in the blood,
including uric acid, potassium, and sodium. A complete chemistry screen (or
SMA-20) looks at the same things as an SMA-7 plus 13 others (such as
phosphorus, carbon dioxide, and bilirubin). Which chemistry screen your doctor
orders depends on why you are having the test, your symptoms, and whether you
have any specific conditions or diseases.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.