Persistent Fatigue: When It's a Warning Sign

Everyone feels tired sometimes. Ordinary tiredness gets better with sleep or a day off. Cancer-related fatigue is different. It does not fully improve with rest, and it can get in the way of daily life. It can be an early sign of some cancers, especially blood cancers. It has many other causes too, so it should be checked rather than assumed.

Leukemia, a cancer of the blood and bone marrow, can cause fatigue early on. Leukemia cells crowd out the bone marrow's ability to make healthy red blood cells, which carry oxygen through your body. Fewer healthy red cells means less oxygen reaching your tissues, which shows up as tiredness. Cancers that cause slow, steady blood loss — such as colon or stomach cancer — can cause the same kind of fatigue through anemia, a low red blood cell count, even without any obvious bleeding you would notice. Many other cancers cause fatigue once they have grown or spread, as the body works harder to cope with the illness.

It is often described as a heavy, whole-body tiredness that sleep does not fix. Simple tasks, like climbing stairs or making dinner, can feel harder than they should. Some people also notice shortness of breath, a fast heartbeat, dizziness, or looking pale — all signs that can go along with anemia.

Poor sleep is one of the most common causes of fatigue, and it is often overlooked. Stress, depression, and anxiety can all cause deep tiredness. Thyroid problems, especially an underactive thyroid, slow the body down and cause fatigue. Infections, some medicines, and low iron without any cancer at all can all be culprits. Most people who feel constantly tired have one of these causes, not cancer.

Your doctor asks how long the fatigue has lasted, whether rest helps, and whether you have noticed other symptoms like weight loss, fever, or bleeding. A complete blood count is one of the first and most useful tests, since it checks your red blood cells, white blood cells, and platelets in one simple blood draw. If it shows anemia, further tests look for the cause, which can include a stool test to check for hidden blood, or an endoscopy to look inside the digestive tract. Thyroid tests are common too, since an underactive thyroid is easy to test for and to treat.

A normal complete blood count is reassuring, and it rules out many causes of fatigue. But it does not rule out every cancer, especially ones that have not yet affected your blood counts. If fatigue continues for several weeks with no cause found, tell your doctor rather than letting it go. Fatigue that does not improve after treating an identified cause, like a thyroid problem, also deserves a second look.

Write down how long you have felt this way. Note whether rest helps at all. Track any other changes, like appetite, weight, or bruising. Bring a list of your medicines too. This short record helps your doctor separate ordinary tiredness from a pattern that needs testing.

• Call 911 or go to an emergency department if you are breathless while sitting still, your chest hurts, or you black out.
• Call your care team the same day if the tiredness comes with bruises you cannot account for, bleeding gums, or a temperature of 100.4°F (38°C) or higher.
• Call your care team within a day or two if you have felt wiped out for several weeks and rest changes nothing, or weight is coming off on its own alongside it.

• Could my fatigue be caused by anemia or another condition?
• What tests would help find the cause?
• Should I have my blood counts checked?
• What changes should prompt me to come back sooner?

• American Cancer Society — Is Anemia a Sign of Cancer?
• American Cancer Society — Signs and Symptoms of Cancer