A physician may order a blood chemistry test to help diagnose an illness. Blood chemistry testing gives a good overview of how the kidneys are functioning and can determine if a patient is dehydrated. This test also measures blood sugar and the acidity of the blood. In an emergency, the results of a blood chemistry test can be back in the doctor's hands in one hour, according to the National Institutes of Health.
Types
Chemistry tests the levels of several substances in the blood. There are two groups of blood chemistry tests: a CHEM-7 and a CHEM-20. A CHEM-7 tests the levels of seven substances, while a CHEM-20 tests those same seven plus an additional 13 blood chemicals. Specifically, a CHEM-7 tests urea nitrogen, carbon dioxide, creatinine, blood sugar, chloride, potassium and sodium.
Preparing for the Test
A patient should fast before having a blood chemistry test. This means he should not have anything to eat or drink for at least six hours, according to University of California, San Francisco. He may have water and medicines, however, unless otherwise directed.
Obtaining a Blood Sample
Blood for testing is usually obtained from veins on the back of the patient's hand or on the inside of the elbow. The area is first cleansed with antiseptic. A tourniquet is wrapped around the upper arm to trap the blood in the lower arm. The vein swells and this increased pressure makes drawing blood easier. A hollow needle is used to break through the skin and enter the vein. An airless test tube is then attached to the other end of the needle; when the tube is punctured, the vacuum inside it is broken, creating a suction that quickly fills the tube with blood. The needle is removed and a bandage is placed over the puncture wound to stop any bleeding.
Risks
Some patients report feeling dizzy or light-headed after having their blood drawn, especially if they have not eaten in six hours. Another risk of having blood drawn is continued bleeding or eventual bruising at the site of the needle-stick. Additionally, infection is always possible any time the skin is broken.
Alternate Names
A blood chemistry test is often called a Chem-7. It is also referred to as a Basic Metabolic Panel. Still others use the term Sequential multi-channel analysis with computer or SMAC-7, according to Medline Plus.
