Why do I need a lab test?

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Your health care provider has told you that you need to have some lab tests. There are many types of lab tests, including blood and urine tests. The samples are collected and then studied, often under a microscope. The results can help your health care provider understand how your body is working.

This will explain what to expect when you need lab tests. It also outlines some of the most common lab tests so you can understand what your health care provider may be looking for when you need these tests.

Why do I need a lab test?

Lab tests are done for many reasons, including to:

  • Check your overall health.
    Some tests are part of a yearly or routine physical so your health care provider can get a clear picture of your health. An example of a general test to get a snapshot of your health is a complete blood count (CBC). You will learn more about this common test later in this booklet.
  • Help diagnose your symptoms
    If you have certain signs and symptoms, your health care provider may run certain tests to help determine whether you have a certain medical condition. This is helpful when there are several medical conditions that could be causing your signs and symptoms. An example is a urine test to see if frequent urination is being caused by a simple urinary tract infection or something more complex, such as diabetes.
  • Diagnose medical conditions that do not have symptoms
    Not all medical conditions have signs and symptoms in the early stages or even at all. Lab tests can help diagnose medical conditions before they are advanced, so you can get treatment sooner. An example is a cholesterol screening. High cholesterol levels usually do not cause any symptoms but can lead to a heart attack or stroke when your arteries are clogged from high levels of cholesterol in your blood.
  • See if treatment is working
    Lab tests help your health care provider know how you are doing with treatment. An example is blood tests to see if your blood thinner medicine is working.

What can I expect when I need a lab test?

Many lab tests do not require any special preparation. You can simply walk in when it is convenient for you and get the test. For certain tests, you may need to fast (not eat or drink anything for a certain number of hours) before your test. Your health care provider should tell you if you need to do this.

If you are having blood work, your blood may be taken from a vein in your arm using a needle or it may be taken from your fingertip with a needle stick. How the blood is taken will depend on the type of blood test you need.

Most people find blood tests to be painless and others feel some minor discomfort. A small number of people may get a bruise at the site where the blood was collected. If you have fainted in the past when having blood work done, please let us know. There are some steps we can take to make you feel as comfortable as possible.

Other types of lab tests require a sample of urine, stool, tissue or other body fluid. We will talk more about these types of lab tests later in this booklet.

Common Blood Tests

There are hundreds of different blood tests available to help health care providers understand what is going on inside your body. This booklet outlines many of the common tests. These tests are often the starting point and more tests may be done if your results from these common tests are abnormal.

    Red blood cell count (RBC count)

    The job of the red blood cell is to carry oxygen from your lungs to the rest of your body. When your RBC count is low, it could mean a number of things including internal bleeding and poor diet. When it is high, it could mean you are dehydrated or have a medical condition such as heart disease.

    White blood cell count (WBC count)

    White blood cells help your body fight infection. If your count is high, it may mean you are fighting an infection. If your count is lower than normal, it may mean your immune system is affected or weakened by a medical condition.

    Complete blood count (CBC)

    This test looks at both your red and white blood cells. It also measures your platelets, which are blood cell fragments that help your blood clot. This is important when you cut yourself so you stop bleeding. The CBC also looks at your hemoglobin, which is the ironrich protein in red blood cells that carries oxygen and hematocrit, which is a measure of how much space your red blood cells take up in your blood flow. All of this information tells your health care provider about your overall health. The CBC test is often done as part of a routine medical exam or physical.

    Blood chemistry tests

    Your blood says a lot about you. Many substances, such as sugar and calcium, are carried in your blood. These substances can affect your health if the levels are too high or too low. For example, if you have too much sugar in your blood you may have diabetes. Or, when blood tests show you don’t have enough B12, you could have a deficiency of that vitamin. Here are some other common blood chemistry tests. You also may hear this group of tests called a metabolic panel.

    Bilirubin – Part of your liver’s job is to break down old red blood cells. A product of red blood cell breakdown is called bilirubin. If your bilirubin levels are too high, it could mean you have a medical condition affecting your liver, gallbladder or bile duct.

    Blood types – If you are having surgery, you likely will have a blood test to find out what your blood type is in case you should need to get extra blood (blood transfusion) during or after your surgery. You will also have a blood type test if you are pregnant. Some people simply want to know what their blood type is and choose to have a blood test so they can find out.

    Blood Urea Nitrogen (BUN)— Urea nitrogen is what forms when protein breaks down. If this test is abnormal, it could mean many things, from a heart condition to liver problems to a low-protein diet. However, it is used most often to check how well your kidneys are working. If this test is abnormal, your health care provider will likely want you to have more tests.

    Calcium – Calcium is important for healthy teeth and bones. Certain health conditions can cause this test to be abnormal. For example, if you have a gastrointestinal condition, your body may not absorb enough calcium from your food during digestion. This would make your calcium level too low. Your calcium level also could be too high. This could be from taking a calcium supplement that you don’t need or from a medical condition.

    Cholesterol – Cholesterol is carried through your blood. There is LDL cholesterol or “bad” cholesterol that is sticky. It can build up and block your arteries. There also is HDL cholesterol or “good” cholesterol, which helps to stop the bad cholesterol from sticking to your artery walls. Finally, there are triglycerides, which are basically fatty particles. You want your bad cholesterol and triglyceride levels to be low to prevent heart disease.

    Creatinine – This test is used to check your kidney function. Many medical conditions can cause this test to be abnormal. The most common reason is diabetes.

    Disease – Some diseases can be detected by a blood test. Human immunodeficiency virus (HIV) and Hepatitis C are two examples.

    Drugs and poisons – Alcohol and illegal drug use can be found through blood tests. Prescription drugs can also be detected and help your doctor see how your treatment is working for you.

    Hormone tests – Hormones are substances in the blood that tell your body what to do. Hormones affect your growth and development, metabolism, sexual function, reproduction and your mood. A common hormone test checks for the human chorionic gonadotropin (HCG) hormone found in the blood when a woman is pregnant.

    Protein – This test is often done to see how well your liver, stomach and kidneys are functioning. If you have an abnormal result, your health care provider will likely order more tests.

    Uric acid – Your body forms uric acid as it breaks down purines, a substance found in some foods. This test is commonly done if your health care provider suspects you have gout, a condition that causes pain and swelling in your feet. This test can also be done to check the health of your kidneys. Aside from eating a diet that is high in purines, abnormal uric acid levels in your blood can be caused by many medical conditions.

    Viruses and bacteria – There are many different types of bacterial and viral infections that can be detected with blood tests. These infections can begin in any part of your body and spread to your blood. You may hear some of these tests called blood cultures. This is because the samples are sent to a lab and watched to see if the bacteria or virus grows. It can take several days to get the results of these tests.

    Blood clotting tests

    These tests are often done before surgery or if you are on a medication that may affect how your blood clots. You may hear the term “coagulation panel” when your health care provider orders these tests to make sure your blood clots properly (not too fast or too slow). You also may need this test if your health care provider thinks you may have a blood clotting disorder.

    Blood enzyme tests

    Just like blood chemistry tests, there are many kinds of blood enzyme tests. One of the most common tests looks for the enzyme troponin that is released during a heart attack.

Common Urine Tests

Your health care provider could send you to get a urine test for many reasons. Below are some of the most common reasons for urine testing.

    Sugar – Your urine should not have any sugar in it. If there is sugar in your urine, you will need more testing. If you have sugar in your urine, it may mean you have diabetes.

    Ketones –Your body makes ketones when it breaks down body fat too quickly to use it as fuel. This can happen when you don’t eat enough sugar or carbohydrates to fuel your body. It can also happen if you are diabetic and your insulin level is not right. If you have ketones in your urine, your health care provider may ask you more questions or send you for more testing. Please note, it is common to have ketones in your urine if you have not eaten anything all day before the test.

    Blood – Your urine should not have any blood in it. If there is blood in your urine, it likely means you have a urinary tract infection or other problem with your urinary tract.

    Bilirubin – Part of your liver’s job is to break down old red blood cells. A product of red blood cell breakdown is called bilirubin. If your bilirubin levels are too high, it could mean you have a medical condition affecting your liver, gallbladder or bile duct.

    Proteins – Many conditions can lead to high protein in your urine, from heart problems to poisoning. If your protein count is too high, you will likely need more lab tests.

    Hormones – Some hormone levels can be checked using a urine sample. One of the most common reasons for a urine test is to detect hormones that are released if you are pregnant.

    Drugs – Many employers require a urine test before they hire someone. Also, most states require random, periodic testing of people who hold certain licenses, such as a commercial driver’s license (CDL).

    Bacteria and other organisms – If you have a urinary tract infection, you likely will have bacteria, parasites or yeast in your urine.

Lab Tests Online

For more information on laboratory testing visit labtestsonline.org.

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