Blood Testing

Blood tests are a standard part of routine and preventive healthcare. A doctor will often order a blood test before or following a physical examination. A doctor may also order blood tests to evaluate specific conditions.
Types
During a routine physical, a doctor may order one of the following tests:
Complete blood count
A complete blood count (CBC) measures a variety of the blood’s components, such as:
red blood cells
white blood cells
hemoglobin
platelets
mean corpuscular volume (MCV) — the average size of a person’s red blood cells
hematocrit — how much space red blood cells take up in the blood
A CBC test helps a doctor identify blood disorders or diseases, such as anemia, issues with clotting, inflammation, infection, or immune system disorders. A person will need to fast before a CBC test only if their doctor asks them to.
Blood enzyme tests
Blood enzyme tests measure the levels of specific enzymes in the body. The body produces enzymes to help control chemical reactions within the body.
Enzyme blood tests can help a doctor identify specific health problems, including a heart attack. If a doctor suspects a heart attack, they will check the levels of the cardiac troponin enzyme, which the heart releases when it is injured.
Blood clotting tests
A blood clotting test, also known as a coagulation panel, looks for a protein that helps the blood to clot. A doctor may order this test if they suspect the person may have a blood clotting disorder.
If a person is taking warfarin or other blood thinning medications, a doctor will likely use a specific blood clotting test as part of routine monitoring.
Lipoprotein panel
If a doctor wants to assess a person’s risk for developing coronary heart disease or other atherosclerotic problems, they will likely order a lipoprotein, or lipid, panel. A lipoprotein panel will provide information about a person’s:
low-density lipoprotein (LDL) cholesterol level
high-density lipoprotein (HDL) cholesterol level
total cholesterol level
triglycerides level in the blood
According to the Department of Health and Human Services, a person will need to fast for 8 to 12 hours before a lipoprotein panel.
If the results indicate abnormal levels of any cholesterol or triglycerides, it could indicate that the person is at higher risk of developing cardiovascular disease.
Basic metabolic panel
The basic metabolic panel (BMP) measures the levels of different chemicals found in the plasma portion of the blood.
The BMP, also known as a blood chemistry 8 test, provides information about the bones, muscles, and organs.
A doctor will tell an individual whether they need to fast before a BMP test, and for how long.
BMP tests look at the following:
Uncorrected calcium levels: Abnormal calcium levels could indicate a person has an underlying condition related to their kidneys or bones, cancer, malnutrition, or other diseases.
Glucose level: Higher than normal blood glucose levels could indicate a person has diabetes or is at risk of developing diabetes. Some people may need to fast before a blood glucose test.
Kidneys: The presence of excess waste products in the blood, such as blood urea nitrogen (BUN) and creatinine, can indicate a problem with the kidneys.
Electrolytes: The presence of abnormal electrolyte levels could indicate an issue with dehydration, kidneys, or other underlying conditions.
Why do some tests require fasting?
What a person eats affects the level of specific components in their blood. For example, a person’s blood sugar level, specifically the glucose level, will rise temporarily after eating.
Typically, a person must not eat for several hours before a blood sugar test.
Other tests also require fasting, such as a fasting lipid panel. A person should check with their doctor whether they need to fast before a test.
Learn more about fasting before a blood test here.