A chemistry screen is a blood test that measures the levels of several substances in the blood (such as electrolytes). A chemistry screen tells your doctor about your general health, helps look for certain problems, and finds out whether treatment for a specific problem is working.
Some chemistry screens look at more substances in the blood than others do. The most complete form of a chemistry screen (called a chem-20, SMA-20, or SMAC-20) looks at 20 different things in the blood. Other types of chemistry screens (such as an SMA-6, SMA-7, or SMA-12) look at fewer. The type of chemistry screen you have done depends on what information your doctor is looking for.
For more information about specific parts of a chemistry screen, see:
Why It Is Done
A chemistry screen may be done:
How To Prepare
How you prepare for a chemistry screen depends on what your doctor is looking for in the test.
Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
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 drawing blood will:
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 pinch.
There is very little chance of a problem from having blood sample taken from a vein.
A chemistry screen is a blood test that measures the levels of several substances in the blood (such as electrolytes).
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:
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.
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