Quick summary

During chemotherapy for breast cancer, a lot hinges on the blood test results that precede each treatment session. Low counts can indicate serious side effects, including fatigue, bruising, and vulnerability to infection -- and can also mean that treatment must be postponed until the body heals.

What a blood test can tell you about breast cancer treatment

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

In the simplest possible terms, 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, among other things, 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.

Here's the shorthand:

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