CHEM-20
Definition
Chem-20 is a group of 20 chemical tests performed on serum (the portion of blood without cells).
These tests include total cholesterol, total protein, and various electrolytes. Electrolytes in the body include sodium, potassium, chlorine, and many others.
The rest of the tests looks at chemicals that help the liver and kidney breakdown various substances.
Alternative Names
SMA20; Sequential multi-channel analysis with computer-20; SMAC20; Metabolic panel 20
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.
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.
Why the Test is Performed
Blood chemistry measures the levels of a number of chemical substances that are released from various tissues in the body. The amounts of these chemicals in the blood may reflect abnormalities in the tissues secreting them.
Normal Results
**Note: Normal or “healthy” values for creatinine can vary with age. There may be declines in kidney function and muscle mass with age, or very high levels of muscle mass in a young athlete. Your physician can interpret these values for you.
Key to abbreviations:
- IU = international unit
- L = liter
- dL = deciliter = 0.1 liter
- g/dL = gram per deciliter
- mg = milligram
- mmol = millimole
- mEq = milliequivalents
Electrolytes:
- Positively charged ions (cations) include sodium, potassium, calcium, and magnesium (usually drawn separately; see magnesium - serum).
- Negatively charged ions (anions) include chloride, bicarbonate (essentially the same as CO2), protein (see total protein), phosphorous, SO4, and organic acids.
When an electrolyte test is performed, the measured ions usually include sodium, potassium, chloride, and bicarbonate. Calcium and magnesium levels are also obtained in many institutions as part of this test.
What Abnormal Results Mean
See the individual tests.
Risks
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Considerations
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Review Date:
3/22/2007
Reviewed By:
Benjamin W. Van Voorhees, MD, MPH, Assistant Professor of Medicine, Pediatrics and Psychiatry, The University of Chicago, Chicago, IL. Review provided by VeriMed Healthcare Network.
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