Blood tests are a familiar part of doctor visits. But what, exactly, do all those tests measure? Do you really need to roll up your sleeve to stay well?
“Blood tests are essential tools for monitoring your health,” says Shazia Qamar, M,D., a family medicine doctor at Henry Ford Health. “Without doing blood tests, it would be really difficult to diagnose many common medical problems such as high cholesterol, diabetes and anemia.”
And those conditions are just a sampling of what your blood can reveal. Here’s your guide to blood tests.
What Do Blood Tests Measure?
There’s a long, long list of things that healthcare providers can measure with a blood test. Those fall into a few categories:
- Routine tests: At your annual physical, your doctor will likely draw blood to run some routine tests. These might include a complete blood count (CBC) and a basic metabolic panel.
- Tests when you have symptoms: If you have signs of a medical problem, a blood test can help diagnose it. If you have fatigue, for example, your doctor might test you for illnesses such as anemia or thyroid diseases, which commonly make people feel tired.
- Screening tests: These tests are done to identify possible problems before any symptoms appear. Depending on your risk factors like age and family history, your doctor might order blood tests to help determine your risk of developing diseases like prostate cancer, for example.
- Pregnancy: Blood tests can confirm a pregnancy and are typically more accurate than urine tests.
- Monitoring: Blood tests also help your healthcare provider monitor your health conditions over time. If you are being treated for high cholesterol, for example, your doctor may test your blood to see how well you’re responding to your medication. If you have prediabetes, regular blood tests can help track whether it progresses into Type 2 diabetes.
- Genetics: Blood tests can determine whether you have inherited genes that might increase your risk of certain disorders, such as some cancers or autoimmune diseases.
Common Blood Tests
Your blood is full of clues to what’s going on inside your body. These common blood tests can reveal a lot about your health.
Complete blood count (CBC)
A complete blood count (CBC) measures the white blood cells, red blood cells and platelets in your blood. It can help diagnose problems such as infections, blood cancers and immune system problems. It can also help identify iron-deficiency anemia (which prevents your blood from carrying enough oxygen to the rest of the body).
Basic metabolic panel/comprehensive metabolic panel
A basic metabolic profile measures several substances in your blood, including glucose (blood sugar) and many of the electrolytes and minerals that your body needs to function. It also measures blood urea nitrogen (BUN) and creatinine, which helps your doctor evaluate your kidney health.
A comprehensive metabolic panel measures all the same substances as the basic panel, plus some additional indicators that provide extra information about kidney and liver health.
Lipid panel
A lipid panel tests lipids in the blood, including:
- LDL cholesterol, which can increase the risk of heart disease
- HDL cholesterol, a protective kind of cholesterol that can reduce your risk of heart disease
- Total cholesterol (the sum of LDL and HDL)
- Triglycerides (fatty substances that also increase the risk of heart disease)
How Often Do You Need Bloodwork?
Whether you need a blood test depends on factors like your age and overall health. Most healthy adults get a CBC every year, and a basic metabolic panel once every few years. Young adults who don’t have high cholesterol should have a lipid panel every five years or so, Dr. Qamar says.
As you get older, your risk for problems like high cholesterol goes up. That means your doctor might recommend more frequent bloodwork.
And if you have a medical condition, regular blood tests are an important tool for monitoring them and making sure your medications are working. People with diabetes, for example, usually get an A1C test every three to six months. That test measures your average blood sugar over the past three months.
But don’t worry too much about figuring out what tests you should have and when. “If you are managing a health problem or have new symptoms, talk to your doctor,” Dr. Qamar says. “They will help decide which tests are needed to help you best manage your health.”
Interpreting Blood Test Results
When it comes to blood tests, there’s usually a range of values that counts as “normal.” If your medical chart shows something a bit higher or lower than that range, that doesn’t always mean there’s a problem. “A few points outside the normal range may not be cause for concern,” Dr. Qamar says.
Blood tests are only one tool. If you do get an abnormal result, your doctor may repeat the test or collect additional information to help make a diagnosis.
Tips for Having Your Blood Drawn
It used to be common to tell people to fast (go without eating or drinking anything but plain water) for eight to 10 hours before having your cholesterol checked. Newer guidelines now say it can be fine to check cholesterol without fasting first. Triglyceride levels, though, can be affected by the food you eat. If your doctor is monitoring your triglyceride level, you’ll be asked to fast before the test.
Whether or not you’re fasting, it’s a good idea to drink plenty of water before having your blood drawn. That makes it easier to find your vein and collect enough blood for the tests.
Feeling anxious? Distraction helps, Dr. Qamar says. Take a deep breath and focus your attention elsewhere. “Don’t look at the needle. Get out your phone or find another way to distract yourself,” she says.
Giving blood might not be fun, but it is important, she adds. “A blood draw is a quick procedure, and well worth it for the information it reveals about your health.”
Reviewed by Shazia Qamar, M.D., a family medicine doctor who sees patients at Henry Ford Medical Center - Warren.
