Blood tests not only help with preventative healthcare but they also help doctors check for certain diseases and medical conditions. While disease prevention is key to a healthy lifestyle, blood tests also help check for proper organ function and a whole lot more.

Blood tests help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working.

Specifically, blood tests can help doctors:

• Evaluate how well organs—such as the kidneys, liver, thyroid, and heart—are working
• Diagnose diseases and conditions such as cancer, HIV/AIDS, diabetes, anemia (uh-NEE-me-eh), and coronary heart disease
• Find out whether you have risk factors for heart disease
• Check whether medicines you’re taking are working
• Assess how well your blood is clotting

Overview

Blood tests are very common. When you have routine checkups, your doctor may recommend blood tests to see how your body is working.

Many blood tests don’t require any special preparations. For some, you may need to fast (not eat any food) for 8 to 12 hours before the test. Your doctor will let you know how to prepare for blood tests.

During a blood test, a small sample of blood is taken from your body. It’s usually drawn from a vein in your arm using a needle. A finger prick also might be used.

The procedure usually is quick and easy, although it may cause some short-term discomfort. Most people don’t have serious reactions to having blood drawn.

Laboratory (lab) workers draw the blood and analyze it. They use either whole blood to count blood cells, or they separate the blood cells from the fluid that contains them. This fluid is called plasma or serum.

The fluid is used to measure different substances in the blood. The results can help detect health problems in early stages, when treatments or lifestyle changes may work best.

Doctors can’t diagnose many diseases and medical problems with blood tests alone. Your doctor may consider other factors to confirm a diagnosis. These factors can include your signs and symptoms, your medical history, your vital signs (blood pressure, breathing, pulse, and temperature), and results from other tests and procedures.

Outlook

Blood tests have few risks. Most complications are minor and go away shortly after the tests are done.

Some of the most common blood tests are:

• A complete blood count (CBC)
• Blood chemistry tests
• Blood enzyme tests
• Blood tests to assess heart disease risk

Complete Blood Count

The CBC is one of the most common blood tests. It’s often done as part of a routine checkup.

The CBC can help detect blood diseases and disorders, such as anemia, infections, clotting problems, blood cancers, and immune system disorders. This test measures many different parts of your blood, as discussed in the following paragraphs.

RED BLOOD CELLS

Red blood cells carry oxygen from your lungs to the rest of your body. Abnormal red blood cell levels may be a sign of anemia, dehydration (too little fluid in the body), bleeding, or another disorder.

WHITE BLOOD CELLS

White blood cells are part of your immune system, which fights infections and diseases. Abnormal white blood cell levels may be a sign of infection, blood cancer, or an immune system disorder.

A CBC measures the overall number of white blood cells in your blood. A CBC with differential looks at the amounts of different types of white blood cells in your blood.

PLATELETS

Platelets (PLATE-lets) are blood cell fragments that help your blood clot. They stick together to seal cuts or breaks on blood vessel walls and stop bleeding.

Abnormal platelet levels may be a sign of a bleeding disorder (not enough clotting) or a thrombotic disorder (too much clotting).

HEMOGLOBIN

Hemoglobin (HEE-muh-glow-bin) is an iron-rich protein in red blood cells that carries oxygen. Abnormal hemoglobin levels may be a sign of anemia, sickle cell anemia, thalassemia (thal-a-SE-me-ah), or other blood disorders.

If you have diabetes, excess glucose in your blood can attach to hemoglobin and raise the level of hemoglobin A1c.

HEMATOCRIT

Hematocrit (hee-MAT-oh-crit) is a measure of how much space red blood cells take up in your blood. A high hematocrit level might mean you’re dehydrated. A low hematocrit level might mean you have anemia. Abnormal hematocrit levels also may be a sign of a blood or bone marrow disorder.

MEAN CORPUSCULAR VOLUME

Mean corpuscular (kor-PUS-kyu-lar) volume (MCV) is a measure of the average size of your red blood cells. Abnormal MCV levels may be a sign of anemia or thalassemia.

Blood Chemistry Tests/Basic Metabolic Panel

The basic metabolic panel (BMP) is a group of tests that measures different chemicals in the blood. These tests usually are done on the fluid (plasma) part of blood. The tests can give doctors information about your muscles (including the heart), bones, and organs, such as the kidneys and liver.

The BMP includes blood glucose, calcium, and electrolyte tests, as well as blood tests that measure kidney function. Some of these tests require you to fast (not eat any food) before the test, and others don’t. Your doctor will tell you how to prepare for the test(s) you’re having.

BLOOD GLUCOSE

Glucose is a type of sugar that the body uses for energy. Abnormal glucose levels in your blood may be a sign of diabetes.

For some blood glucose tests, you have to fast before your blood is drawn. Other blood glucose tests are done after a meal or at any time with no preparation.

CALCIUM

Calcium is an important mineral in the body. Abnormal calcium levels in the blood may be a sign of kidney problems, bone disease, thyroid disease, cancer, malnutrition, or another disorder.

ELECTROLYTES

Electrolytes are minerals that help maintain fluid levels and acid-base balance in the body. They include sodium, potassium, bicarbonate, and chloride.

Abnormal electrolyte levels may be a sign of dehydration, kidney disease, liver disease, heart failure, high blood pressure, or other disorders.

KIDNEYS

Blood tests for kidney function measure levels of blood urea nitrogen (BUN) and creatinine (kre-AT-ih-neen). Both of these are waste products that the kidneys filter out of the body. Abnormal BUN and creatinine levels may be signs of a kidney disease or disorder.

Blood Enzyme Tests

Enzymes are chemicals that help control chemical reactions in your body. There are many blood enzyme tests. This section focuses on blood enzyme tests used to check for heart attack. These include troponin and creatine (KRE-ah-teen) kinase (CK) tests.

TROPONIN

Troponin is a muscle protein that helps your muscles contract. When muscle or heart cells are injured, troponin leaks out, and its levels in your blood rise.

For example, blood levels of troponin rise when you have a heart attack. For this reason, doctors often order troponin tests when patients have chest pain or other heart attack signs and symptoms.

CREATINE KINASE

A blood product called CK-MB is released when the heart muscle is damaged. High levels of CK-MB in the blood can mean that you’ve had a heart attack.

Blood Tests To Assess Heart Disease Risk

A lipoprotein panel is a blood test that can help show whether you’re at risk for coronary heart disease (CHD). This test looks at substances in your blood that carry cholesterol.

A lipoprotein panel gives information about your:

• Total cholesterol.
• LDL (“bad”) cholesterol. This is the main source of cholesterol buildup and blockages in the arteries. (For more information about blockages in the arteries, go to the Diseases and Conditions Index Atherosclerosis article.)
• HDL (“good”) cholesterol. This type of cholesterol helps decrease blockages in the arteries.
• Triglycerides. Triglycerides are a type of fat in your blood.

A lipoprotein panel measures the levels of LDL and HDL cholesterol and triglycerides in your blood. Abnormal cholesterol and triglyceride levels may be signs of increased risk for CHD.

Most people will need to fast for 9 to 12 hours before a lipoprotein panel.

Blood Clotting Tests

Blood clotting tests sometimes are called a coagulation (KO-ag-yu-LA-shun) panel. These tests check proteins in your blood that affect the blood clotting process. Abnormal test results might suggest that you’re at risk of bleeding or developing clots in your blood vessels.

Your doctor may recommend these tests if he or she thinks you have a disorder or disease related to blood clotting.

Blood clotting tests also are used to monitor people who are taking medicines to lower the risk of blood clots. Warfarin and heparin are two examples of such medicines.