For many patients, a blood test is one of the least-liked parts of a physical. But when your doctor needs a quick, meaningful look at your health, a blood test is priceless.
That’s because blood doesn’t keep secrets: If something’s amiss inside, your corpuscles, or blood cells, are usually the first to know. Their behavior, content and condition help reveal what’s ailing you.
Case in point: Blood tests are the gold standard for evaluating your risk of heart disease. Tests look at:
- Lipids. A blood serum test shows how much HDL (“good”) and LDL (“bad”) cholesterol you have and if triglyceride levels are high. Healthy people—total cholesterol < 200 milligrams per deciliter (mg/dL), LDL < 100 mg/dL, HDL > 60 mg/dL and triglycerides < 150 mg/dL—should have this test every five years beginning at age 20.
- Cardiac enzymes. If this test finds enzymes are leaking from the heart muscle, it signals that a heart attack has struck or is imminent.
- Oxygen. Blood in the arteries should be oxygen-rich. If this test shows oxygen is lacking, there may be a problem with your heart or lungs, or a tumor or disease may be depleting oxygen from the bloodstream. Your doctor may perform this test if you have risk factors for heart disease.
Other tests can find signs of diabetes, leukemia, alcoholism, lupus, bone marrow disorders and anemia. For instance, a complete blood count (CBC) measures the concentration of:
- red blood cells
- oxygen-carrying hemoglobin in red blood cells
- white blood cells
- platelets (which help blood clot to prevent bleeding)
A similar test—a blood chemistry workup—checks the health of your liver and kidneys by measuring amounts of sodium, potassium, calcium, blood sugar and bilirubin in the bloodstream.
Some blood tests look for so-called antigens, enzymes produced by specific diseases. For example, men should talk with their doctors about the benefits of a prostate-specific antigen (PSA) test for prostate cancer annually beginning at age 50.
Another test searches for abnormal levels of thyroid hormones, which can cause many symptoms including unexplained weight gain or loss, fatigue or trembling hands. This test is recommended for everyone after age 60, then as directed by a physician.
Still another test looks at how much iron is bound to a blood protein called transferrin. Too much iron indicates hemochromatosis, a treatable genetic disease that can contribute to diabetes, arthritis, cardiovascular disease and cirrhosis of the liver. Women should have this test once at age 18 and again after menopause; men, around age 30.
There’s even a blood test for allergies to drugs or insect bites. However, most doctors prefer skin tests for allergies—they’re accurate and painless.
Giving a quality blood sample is important to your health. These tips will help.
- Make time. Fast for the proper amount of time. Most tests call for “overnight” fasting—eight to 12 hours. And be an early bird the next morning—grab the earliest appointment for the test so you can have breakfast at a reasonable hour afterward.
- Water it. Drink only water during a fast. Any other food or beverages could skew the test results and require a do-over.
- Keep your head. If having blood drawn makes you squeamish, ask the lab tech to help you through (they’re trained for it). Other ideas: Watch the clinic TV, hum or close your eyes and recall a comforting place or a happy face.