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What Do Common Blood Tests Check For?

Test can indicate disorders, infection, immune system problems

A young woman smiles after completing her blood test.

Test can indicate disorders, infection, immune system problems

Blood tests are among the most common types of diagnostic tests. The test itself is simple and the results can help your doctor check for a wide range of issues.

“From checking your cholesterol levels and thyroid function to diagnosing infections, diseases and other conditions, blood tests are often the first step in diagnosing dozens of conditions,” says Fatma Deif, MD, an internal medicine physician at Scripps Clinic Rancho San Diego.

When your doctor orders a blood test, a health care professional called a phlebotomist will use a needle to take a sample of your blood, usually from a vein in your arm. The test is fast and typically not painful, but you may feel a sharp prick when the needle is inserted into the vein. The process takes just a few minutes.

Here are some of the most common blood tests:

Complete blood count

A complete blood count (CBC) can provide an overview of your health or can help your doctor look for a specific condition. This test measures several parts of your blood that can indicate potential problems, including:

Red blood cells carry oxygen from your lungs to your entire body. Low red blood cell counts may indicate disorders, such as anemia or blood loss.

White blood cells help with immunity, so low counts may be a sign of infection or immune system problems. There are different types of white blood cells; a blood differential test measures each type.

Platelets help your blood clot. Low platelet levels may lead to too much bleeding; high levels may raise your risk of blood clots.

Hemoglobin is a protein that carries oxygen. Problems with hemoglobin can cause anemia and other disorders.

Hematocrit measures how much space red blood cells use in your blood. If you have anemia, your hematocrit may be low, while dehydration may cause it to be high. Hematocrit levels also may signal a blood or bone marrow disorder.

Mean corpuscular volume (MCV) measures the average size of your red blood cells. Abnormal levels may indicate a disorder.

Basic metabolic panel

A basic metabolic panel (BMP) is a group of tests that measures the various chemicals in your blood. It includes tests for blood glucose, calcium and electrolytes, which are minerals in your blood.


“The BMP gives us a wealth of information about your heart, muscles, bones and organs, such as your liver and kidneys,” says Dr. Deif. “Your doctor may instruct you to fast for several hours or overnight before having some of these tests.”

Blood enzyme tests measure the amounts of enzymes, which are chemicals that help control the body’s chemical reactions. There are many blood enzyme tests. One of the most common can help determine if you have had a heart attack and if your heart muscle is damaged.

Lipoprotein panel measures your HDL (“good”), LDL (“bad”) and total cholesterol levels, as well as your triglycerides, a type of fat. It can provide information about your risk of coronary heart disease (CHD). You may need to fast for up to 12 hours before a lipoprotein panel.

Quantitative hCG blood test is most often used to test for pregnancy. The human chorionic gonadotropin (hCG) blood test measures the level of hCG hormone in your blood. It also may be done to test for breast, lung, uterine or ovarian cancer.

Ammonia blood test measures ammonia, which is a waste product created when your body breaks down protein. If too much ammonia builds up in your blood, it can result in extreme fatigue, neurological problems, coma or death.

CO2 test measures the amount of carbon dioxide in your blood. Abnormal levels may indicate kidney, respiratory or metabolic issues.

Coagulation panel, also known as a blood clotting test, measures the levels of proteins that determine how quickly your blood clots. This test is often ordered for people who take blood thinning medication, such as coumadin, to ensure that they are taking the correct dosage for their needs.

Educate yourself about blood tests

If your doctor recommends a blood test, be sure you understand what the test measures and if you need to do anything to prepare for it.