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How Blood Test Results Can Affect Chemotherapy

By , Caring.com senior editor
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What a blood test can tell you

When someone is undergoing chemotherapy to treat cancer, a lot hinges on the blood test results that precede each chemotherapy session. Low counts can indicate serious side effects, including fatigue, bruising, and vulnerability to infection -- and can also mean that treatment must be postponed while his body heals.

Complete blood counts, or CBCs, are routinely performed during chemotherapy and other cancer treatments to check the number of each type of blood cell circulating in the body. This test is also called a hemogram.

White blood cells, or neutrophils, fight infection; red blood cells, also known as erythrocytes, pick up oxygen in the lungs and carry it to the tissues. CBCs note any shortage of red blood cells, which is the definition of anemia and leads to low oxygen levels in the blood. In addition, CBCs count platelets, which are components of red blood cells that enable blood to clot.

  • Low red blood count = fatigue, low energy
  • Low platelets = bruising and bleeding
  • Low white blood count = susceptibility to infection

What are normal ranges for CBCs?

These vary a bit depending on the lab, so the ranges that follow are guidelines rather than absolutes. Be sure to ask for a copy of the CBC each time it's performed, and look at the lab results sheet for the normal range for that lab. Still, there are some general rules of thumb:

Red blood cells (RBC)
Normal for men: 4.5 to 6.2 million per microliter (a single drop)
Normal for women: 4.2 to 5.4 million per microliter

White blood cells
Normal for men and women: 3,700 to 10,000 per microliter
Lowest level at which someone is safe from infection: 1,000

Normal range for men and women: 150,000 to 450,000 per microliter
Lowest level at which someone's blood can still clot normally: 100,000
Level at which there's a risk of spontaneous bleeding: 50,000
Level at which bleeding can become life-threatening: 5,000