CHEM-20

Definition:

Chem-20 is a "battery" 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 (see the Normal Values). The rest of the tests focus primarily on chemicals related to the body's metabolism and the breakdown of various substances. These would be tests that allow us to evaluate the function of the liver and kidney.

Alternative Names:

SMA20; Sequential multi-channel analysis with computer-20; SMAC20; Metabolic panel 20

How the test is performed:

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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 cleansed 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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to prepare for the test:

Overnight fasting is preferable.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

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.

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 Values:

albumin: 3.9 to 5.0 mg/dl
alkaline phosphatase: 44 to 147 IU/L
ALT (SGPT): 6 to 59 IU/L
AST (SGOT): 10 to 34 IU/L
BUN: 7 to 20 mg/dl
calcium - serum: 8.5 to 10.9 mg/dl
serum chloride: 101 to 111 mmol/L
CO2: 20 to 29 mmol/L
creatinine: 0.8 to 1.4 mg/dl
direct bilirubin: 0.0 to 0.3 mg/dl
gamma-GT: 0 to 51 IU/L
glucose test: 64 to 128 mg/dl
LDH: 105 to 333 IU/L
phosphorus - serum: 2.4 to 4.1 mg/dl
potassium test: 3.7 to 5.2 mEq/L
serum sodium: 136 to 144 mEq/L
total bilirubin: 0.2 to 1.9 mg/dl
total cholesterol: 100 to 240 mg/dl
total protein: 6.3 to 7.9 g/dl
uric acid: 4.1 to 8.8 mg/dl

Note: ALT = alanine transaminase, AST = aspartate aminotransferase, BUN = blood urea nitrogen, CO2 = carbon dioxide, gamma-GT = gamma-glutamyl transpeptidase, LDH = lactate dehydrogenase; IU = international unit, L = liter, dl = deciliter = 0.1 liter, 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.

What the risks are:

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

Special 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: 11/7/2001
Reviewed By: Jeffrey Heit, M.D., Department of Medicine, University of Pennsylvania Health System, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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