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Understanding Blood Tests

Blood travels to every part of the body, transporting elements related to most all of our body functions. Cells in the blood (red cells, white cells and platelets) serve essential roles related to oxygen delivery, fighting infection and blood clotting. In addition, may other molecules needed for our body to function (e.g. nutrients, hormones, enzymes, waste products) are delivered and removed by the blood. This makes blood an ideal source for vital information about health and to uncover the mystery of disease.. Not only is blood a wonderful way to find this information, it is very easy to get a blood sample and to measure it!

Standard Tests

There are many blood tests available for specific health conditions and diseases, but there are also some tests that are common in assessing health for a number of routine health and disease concerns. These groups of tests will be described below so that you have an idea about the kind of information that might be available when your doctor orders a test. In addition, you can always ask your doctor what specific tests he/she is going to order and what they are likely to show. That can be very helpful in working with your doctor to stay healthy, find new health concerns, or follow progress in an ongoing health condition you may have.

When you look at your test results, you will see your measurement and what the range is for a test to be normal. A test outside that range can indicate specific conditions and/or give clues for next steps.

1. Complete Blood Count (CBC)

A Complete Blood Count (CBC) measures the number of blood cells (i.e. red cells, white cells and platelets). It also includes other red cell measurements such as hematocrit, which is the percent of your blood made up of red cells. Red cell measurements can show whether or not you have anemia (too few red blood cells). White blood cells are important in fighting infection and can go up or down in certain conditions. If you have a bacterial infection, for example, numbers increase rapidly. White blood cells can decrease with other conditions including viral infection and as a side effect of certain medicines and radiation therapy. Having a low white blood cell count is significant as your ability to fight infection can be decreased.

The white blood cells measurements can be broken down even further by a differential. This test will show the percent of each of five kinds of white blood cells. Since each kind of white cell has a different role this can help in diagnosing a number of conditions such as the kind of infection you have or whether there are signs of leukemia.

2. Blood Chemistry Tests

Blood chemistry tests are often done to check on important body systems. A “basic metabolic panel” will include glucose which could point to diabetes and electrolytes (sodium, potassium, chloride and carbon dioxide) which relate to the fluid balance needed for other systems (e.g. heart, muscles and brain) to function. Basic panels can also include specific tests for specific organs like bone, kidneys and liver.

3. Tests for Heart Disease and Stroke Risk

A set of tests used to assess risk for heart disease and stroke is a lipid panel. This test measures parts of your blood that can contribute to plaque buildup including:

  • Total Cholesterol
  • LDL (“Bad”) Cholesterol – cholesterol that causes plaque buildup
  • HDL (“Good”) Cholesterol – cholesterol that decreases plaque buildup
  • Triglycerides – a kind of blood fat that can indicate risk

4. Blood Clotting Tests

Blood Clotting tests check for proteins in the blood that affect the clotting system. The tests also monitor the effects of certain medications that are used to avoid clotting. Blood Clotting tests are commonly given in preparation for surgery to ensure that the patient will not bleed excessively during surgery.

5. Blood Type

Your blood type is not a test that is checked routinely by your doctor. To find out your blood type you can ask about doing that test. Another way you can find out your blood type is to donate blood. Two days after you donate blood at the American Red Cross you can call their donor assistance line to find out your blood type: 866-236-3276.

Learn more:

Types of Blood Tests (National Heart Lung and Blood Institute)

What do Blood Tests Show (National Heart Lung and Blood Institute)

For more information:

Go to the Blood and the Body health topic.