Sequential multi-channel analysis with computer-20
Key points
- Chem-20 is a group of 20 chemical tests performed on serum (the portion of blood without cells).
- Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand.
- The area is cleaned with antiseptic and punctured with a sharp needle or a lancet.
- The patient should try not to eat overnight before the test.
Alternative names
SMA20; CHEM-20; SMAC20; Metabolic panel 20
Definition
Chem-20 is a group of 20 chemical tests performed on serum (the portion of blood without cells). Electrolytes are ionized salts in blood or tissue fluids (ions are atoms or molecules that carry an electrical charge). Electrolytes in the body include sodium, potassium, chlorine, and many others.
The rest of the tests focus primarily on chemicals related to the body's metabolism and the breakdown of various substances. These are tests that evaluate the function of the liver and kidneys.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleaned with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test
The patient should try not to eat overnight before the test.
Infants and children:
The preparation you can provide for this test depends on your child's age, previous experience, and level of trust. For general information regarding how you can prepare your child for a test, see the following:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- Schoolage test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Written and revised by
Andrey Nailor, M.D.
Our doctors write and review articles for accuracy and keep them up to date.
health.am provides general information, not medical advice. Always consult a qualified health professional about your own health.