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, like the kidneys, liver, and heart, are working.
- Diagnose diseases and conditions such as cancer, HIV/AIDS, diabetes, anemia (uh-NEE-me-eh), and coronary Heart disease (also called coronary artery disease).
- Learn whether you have risk factors for Heart disease.
- Check whether medicines you’re taking are working.
How is a blood test carried out?
Blood samples can be taken either from a vein or from an artery. If only a few drops of blood are needed it is enough to make a small prick in the tip of the finger and then squeeze the blood out.
Most blood test samples are taken from a vein. The vein used for blood sampling is usually on the inside of your elbow or back of your wrist. A tourniquet (tight band) is usually placed around your upper arm. This makes the vein fill with blood and makes it easier for the blood sample to be taken.
The injection site is cleaned with swab usually containing spirit and then a needle is carefully inserted into the vein.
The needle will be attached either to a low pressure blood test tube (Vacutainer), or to a syringe where the plunger is pulled back to create low pressure.
When the required amount of blood has been extracted, the needle is carefully removed and a swab or piece of cotton wool is held over the wound. After one or two minutes the cotton wool or swab is removed and a sticking plaster is applied.
Types of Blood Tests
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.
Sexually Transmitted Diseases
A blood test is a diagnostic test used to determine whether you have syphilis, hepatitis B, or HIV.
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.
Toxoplasmosis
The results of the blood test will determine if you have the toxoplasmosis infection. Toxoplasmosis is harmless to you, but it may cross the placenta and cause harm to the baby.
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 Health Topics 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.