A blood test is one of the most common tests healthcare providers use to monitor your overall health or help diagnose medical conditions. You may have a blood test as part of a routine physical examination or because you have certain symptoms.
Blood tests are common medical tests. You may have a blood test as part of a routine physical examination or because you have certain symptoms.
There are many different blood tests. Some tests focus on your blood cells and platelets. Some evaluate substances in your blood such as electrolytes, proteins and hormones. Others measure certain minerals in your blood.
Regardless of why you’re having a blood test, it’s important to remember that blood tests help healthcare providers diagnose health issues. But blood test results aren’t diagnoses. An abnormal blood test result may not mean you have a serious medical condition.
Your blood plays a big role in your overall health and contains a lot of information about what may be going on in your body. That’s one reason why blood tests are a common medical test. A healthcare provider may do a blood test because:
In a broad sense, a blood test shows changes in your body. Blood test results don’t show a complete picture. Instead, they’re a kind of snapshot. After seeing that snapshot, your provider may do other blood tests to get a closer view. Here’s a glimpse of what your healthcare provider may see with blood tests:
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
There are many different blood tests. Some tests — such as complete blood count tests, basic metabolic panels, complete metabolic panels and electrolyte panels — check on several different elements in your blood at the same time. Other blood tests look for very specific elements in your blood.
This is the most common blood test that includes several specialized tests. CBC tests:
A basic metabolic panel (BMP) measures several substances in your blood. Healthcare providers use BMPs to evaluate your overall health and screen for or monitor health issues. A BMP may include a:
Comprehensive metabolic panels (CMP) include all the blood tests done as part of a basic metabolic panel. Additional blood tests include:
Electrolytes are minerals in your blood. Imbalance with electrolytes may be a sign of issues with your heart, kidneys or your lungs. An electrolyte panel includes all electrolyte tests in BMPs and CMPs. Additional electrolyte levels tested include magnesium and anion gap. Magnesium supports your brain, heart and muscles. Anion gap tests check the acid-base balance in your blood.
While the various blood and electrolyte panel tests provide a lot of information, there are disease-specific blood tests that help providers diagnose and treat specific conditions.
Autoimmune diseases happen when your immune system accidentally attacks your body instead of protecting it from intruders like viruses, parasites and cancer. Your provider may order the following blood tests:
Healthcare providers may use several different tests to diagnose and treat cancer, blood cancer and noncancerous blood disorders.
Blood tests for cancer fall into four basic categories — complete blood count, tumor markers, blood protein testing and circulating tumor tests. CBC, tumor markers and circulating tumor tests may help detect some solid tumors. Blood in your poop (stool) or pee (urine) may also be a sign of cancer.
A CBC measures red and white blood cell and platelet levels. Abnormally high or low blood cell or platelet levels may be a sign of some types of cancer.
Tumor markers are substances made by cancerous cells or your body’s normal cells in response to cancer. Tumor marker blood tests include:
The circulating tumor test is a relatively new blood test for cancer. This test looks for cancerous cells that have broken away from a tumor and into your bloodstream. Currently, it can help monitor certain types of cancer, such as breast, prostate and colorectal cancers. Scientists are still developing the technology.
Healthcare providers may use the same tests to diagnose blood cancer or noncancerous blood disorders:
Some blood tests don’t involve providing blood samples, such as:
Your endocrine system is made of organs called glands. Glands produce hormones. Healthcare providers may use blood tests to diagnosis conditions affecting parts of your endocrine system. Common blood tests include:
Some blood tests evaluate your risk of developing heart disease:
Your healthcare provider may recommend specialized blood tests, including:
That depends on your situation and your overall health. Most healthcare providers recommend annual physical examinations that may include a complete blood count test. In general, providers recommend tests based on what they know about you. For example, they may recommend regular blood glucose tests if you have overweight (a Body Mass Index or BMI over 25) or obesity (a BMI greater than 30).
That depends on the kind of test you’re having. For example, some blood tests require you to fast for several hours before the test. You may be asked not to drink any liquids apart from a few sips of water. Most blood tests don’t require fasting, but it’s a good idea to ask your healthcare provider what to avoid before your blood test. Other steps may include:
Phlebotomists — healthcare providers with special training in drawing blood — do blood tests. During the blood test process:
All blood tests involve obtaining blood samples. Venipuncture (from a vein) is the most common procedure. Other procedures are:
That depends on the kind of blood test. On average, a complete blood count (CBC) test may take as much as 30 milliliters (mL) of blood. It may sound like a lot of blood, particularly if you’re watching your blood flow into several sample tubes. But it’s not — the average adult has 4,500 to 5,700 milliliters of blood in their body.
They can, depending on the kind of blood test you have. It’s important to remember that phlebotomists receive training on how to obtain blood samples quickly and without causing pain.
That said, tests that take blood from an artery tend to hurt more than tests that take blood from a vein. And with venipuncture, taking blood from a vein may hurt a bit if the phlebotomist has trouble inserting the needle into your vein. Let your phlebotomist know if you have any discomfort. They’ll try different ways to obtain samples of your blood.
Many people feel anxious about blood tests. Some ways to cope include:
Your provider will put a bandage on the spot where the needle went in. Depending on the blood test, they may recommend you rest for a minute or so before standing up and leaving.
That depends on the blood test and your provider’s preferences. Your provider likely will explain how you’ll receive results. Some blood test results are available within a few hours. Others, like genetic test results, typically take longer.
Some healthcare organizations offer online access to test results. But your provider may prefer to discuss your results in a telephone conversation or in person.
Not necessarily. If your tests were part of your routine medical checkup, your healthcare provider may want to review results with you. They may have recommendations about ways you can improve your health. If you’ve received treatment for a medical condition, your provider may want to discuss your test results in detail and put the results in context.
A note from Cleveland Clinic
It’s probably fair to say blood tests are last on most people’s list of fun things to do. But blood tests are an essential tool healthcare providers use to monitor your overall health or diagnose medical conditions. You may have a blood test as part of a routine physical examination or because you have certain symptoms.
Regardless of why you’re having a blood test, it’s important to remember that while blood tests help providers diagnose health issues, they aren’t diagnoses. An abnormal blood test result may not mean you have a serious medical condition. If your healthcare provider recommends blood tests, they’ll be glad to explain why they recommend the test and what the test may show.
Last reviewed by a Cleveland Clinic medical professional on 12/06/2022.
Learn more about our editorial process.