5 Important Blood Tests Beyond the Basics

They May Be Worth Pursuing in Certain Situations

Bring this article to your next doctor appointment to ask if these tests are right for you.

Your next general check-up will probably include basic blood tests for levels of red blood cells, various types of white blood cells, fats (like cholesterol), and chemicals that indicate how your liver and kidneys are functioning. Some tests beyond the basics can also reveal important aspects of health, but your doctor might not offer them routinely. The following five tests may be worth pursuing in certain situations.


B12 (cobalamin) is an essential vitamin we need for keeping our brain and nerves healthy, for producing DNA and red blood cells, and for lowering levels of homocysteine (an amino acid linked to chronic diseases such as dementia and heart disease).

Our B12 comes from food, including beef, eggs, poultry, and dairy foods (milk, yogurt). To absorb the vitamin, we need stomach acid to shake it loose from food. Then a protein called intrinsic factor (made in the stomach lining) binds to B12 so it can be absorbed by the small intestine and passed into the blood.

Some people have low B12 levels. There are several common reasons for this:

They are vegetarians and don't eat B12-rich foods.

They produce less stomach acid than they used to.

They use medications that reduce stomach acid, such as antacids for heartburn.

They have a rare autoimmune disease (pernicious anemia) that leads to severe B12 deficiency.

Should you get the test? "I think everybody should get at least one B12 test after age 65, and then get tested every few years. Low B12 levels can lead to anemia, memory problems, and walking difficulty," says Dr. Suzanne Salamon, associate chief of gerontology at Harvard-affiliated Beth Israel Deaconess Medical Center.

Normal B12 test results range from 160 to 950 picograms per milliliter (pg/mL). A low-normal test result in the range of 200 to 300 pg/mL may warrant a vitamin B12 supplement.


We get a little vitamin D in our diet (from foods like fish, fortified milk, or yogurt), but most of it is manufactured by our bodies when the sun's ultraviolet B rays shine on our skin. That's why D is known as the "sunshine vitamin." Still, many older adults are deficient in vitamin D, no matter how sunny their environment. "It doesn't matter if you live in Florida or California because, as you get older, your skin doesn't absorb sunlight as well," Dr. Salamon says.

You don't want to let vitamin D levels drop. Vitamin D is important for healthy bones, calcium absorption, inflammation reduction, immune function, and other body processes, and it may play a role in keeping cancer in check. As we reported in June 2021, recent Harvard evidence suggests that taking a daily vitamin D supplement is associated with a reduced risk for advanced cancer in healthy-weight midlife or older-age people.

Should you get the test? Dr. Salamon recommends a baseline test at least once in your life, especially if you have brittle bones or a stomach condition that affects your ability to absorb vitamin D. But she points out that screening is hotly debated.

What if you have a high risk for cancer? "While you may feel better knowing what your vitamin D levels are, an alternative is to skip the test and just start taking a supplement of 1,000 to 2,000 international units per day. If adding another pill to your regimen would overwhelm you, talk to your doctor about it first," says Dr. JoAnn Manson, Harvard's leading vitamin D researcher and chief of the Division of Preventive Medicine at Harvard-affiliated Brigham and Women's Hospital.

A normal result for a vitamin D test measuring a form of the vitamin (25-hydroxyvitamin D) is debated, but should be at least 20 nanograms per milliliter (ng/mL).

Blood research, Scientist hand holding test tube with blood in laboratory.(Getty Images)


Hepatitis C is a viral infection that can lead to cirrhosis, liver damage, liver cancer, or liver failure. It's spread when a person comes in contact with the blood of an infected person, which can happen with intravenous drug use; having sex with an infected partner; getting a tattoo or body piercing with unsterile equipment; sharing razors, nail clippers, or toothbrushes; or having had a blood transfusion before 1992 (when the blood test for hepatitis C first became available).

Baby boomers (born between 1945 and 1964), who are five times more likely to have the virus than other adults, may have become infected in the 1960s through the 1980s. Yet only about 13% of baby boomers had been tested by 2015. "It could be due to the stigma, but I wouldn't be surprised if a lot of doctors don't offer the test. They may think their patients aren't at risk for hepatitis C," Dr. Salamon says.

Should you get the test? All U.S. adults should be tested at least once, and more often if they take part in risky behavior. The good news: "There's a cure for hepatitis C if you catch the infection early," Dr. Salamon says.

4. HIV

Since HIV (human immunodeficiency virus) and AIDS (the late-stage phase of HIV infection) first appeared decades ago, we've developed powerful antiviral medications to keep the infection from progressing. But like hepatitis C testing, HIV testing also has a stigma.

HIV is transmitted when someone is exposed to certain body fluids of an infected person. That can happen during vaginal or anal sex or the sharing of drug equipment such as needles.

Should you get the test? The CDC advises everyone ages 13 to 64 get tested at least once, and warns that older adults are less likely to be screened because they (or their doctors) don't think they're at risk for HIV. Yet one in six people diagnosed with HIV in 2018 was age 50 or older. "Get this test if you've never had it before or if you're sexually active," Dr. Salamon advises.


People with diabetes or prediabetes have elevated levels of glucose (sugar) in the blood. A blood sugar measurement taken after fasting may be ordered during a check-up and is covered by Medicare. But Dr. Salamon says primary care physicians don't always check your levels each year.

Should you get the test? If your blood sugar is normal, a test every few years is fine, but it still might be a good idea to get annual testing. "Some people are 'silent' diabetics who don't have symptoms, and you wouldn't pick this up unless you ordered the test," Dr. Salamon says. People at high risk for diabetes, such as those who are overweight or have diabetes in their family, may need more frequent tests.

 A normal fasting blood sugar measurement is less than 100 milligrams per deciliter (mg/dL) of blood; 126 or more can indicate diabetes. "But normal levels change with age and can be slightly higher. Your doctor must interpret the results," Dr. Salamon says.


This article was published by Harvard Health Letter.

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