Iris Oncology
Diagnosis and Treatment

Understanding Cancer-Related Tests: The Complete Blood Count (CBC)

As you go through cancer diagnosis, treatment, and follow-up care, your doctor will probably order routine blood tests for you. Bloodwork is necessary to monitor your general health and to check for potential side effects of your treatment regimen. One of the tests that your doctor will order most frequently is the Complete Blood Count (CBC).  

The CBC measures the number and proportion of several types of cells in your blood. Shortly after you’ve had your CBC blood test drawn, you’ll likely receive your results either as a printout from your oncology team or through an electronic system. Your results will be filled with lists of important numbers that can help you better understand your health — that is, once you first understand what the numbers in your results are and why they’re important. 

All of the numbers in a CBC have an established “normal” range. Different labs can have different ranges of normal. Your results will tell you and your doctor whether your values are within that range and, ultimately, give you a good idea of how your cancer and its treatment are impacting your overall health.   

It's normal for blood test values to fluctuate slightly. Many different factors can cause blood levels to be slightly out of normal range, which by themselves may not be concerning. For example, various cancer treatments — as well as the cancer itself — can all cause lower or higher-than-normal values.  

As you begin learning to read your own lab results, here’s a value-by-value guide to help you get started.   

Lab Value 


What do abnormal values mean to me? 

Signs and symptoms of Abnormal Values 

White blood cell count (WBC)  

WBCs move around the body to find and fight infections.   

When your white blood cell count is low, you may be more likely to get infections. When your white blood cell count is high, it may be a sign that you have an infection.   

-Signs of infection might include:  

-Fever ( > 100.4F temperature) 

-Urinary frequency or pain with urination 



-Sore throat 


-Abdominal pain 


-Pain or tenderness around a wound 

Absolute Neutrophil Count (ANC) 

Neutrophils are a specific type of white blood cell that helps prevent against infections. 

Many cancer treatments can cause neutropenia (which is a fancy way of saying you have a low number of neutrophils). This can make you more susceptible to infections and normal signs of infection may be delayed or not present at all. 

-Fever ( > 100.4 F temperature) When neutropenia occurs, fever is often the only sign of infection, and infections can become severe very quickly.  For that reason, fevers of 100.4 or higher or other signs of infection are considered a medical emergency, notify your oncology team immediately.  



 and Hematocrit 


Hemoglobin is a protein in your red blood cells that carries oxygen from your lungs to the rest of your body. A hemoglobin test measures the level of red blood cells present in your blood.  


Hematocrit reflects the percentage of your blood volume that is composed of red blood cells. 

Low readings may indicate a low supply of red blood cells, either because the bone marrow is not producing enough red blood cells, or because cells are being destroyed faster than they are being made.

When hemoglobin and or hematocrit are low, you may not have enough red blood cells to carry oxygen throughout your body – this is a condition called anemia.  Lower than normal values can also be a sign of blood loss.  



-Pale skin 

-Irregular heartbeats 

-Shortness of breath 

-Dizziness or lightheadedness 

-Chest pain 

-Cold hands or feet 




Platelets are the part of your blood that helps to stop bleeding by clumping and forming plugs, called blood clots.   

When your platelets are low – called thrombocytopenia — you are at a higher risk of bleeding.  

-Easy bruising 

-Tiny red spots under the skin 

-Bleeding from gums or nose 

-Excessive bleeding from a small cut 

-Blood in urine 

-Vomiting up blood 

-Blood in stool 

If you have any questions regarding your blood test results or if you are experiencing any of the symptoms described, contact your oncologist. You can also reach out to an Iris nurse for additional support — we’re here for you any day, anytime. 

Lee, S. (n.d.). Low platelet count (thrombocytopenia). Canadian Cancer Society. Retrieved December 30, 2021, from 

 Mayo Foundation for Medical Education and Research. (2020, April 8). Thrombocytopenia (low platelet count). Mayo Clinic. Retrieved December 30, 2021, from 

Mayo Foundation for Medical Education and Research. (2021, September 8). Anemia. Mayo Clinic. Retrieved December 30, 2021, from 

NCI Dictionary of Cancer terms. National Cancer Institute. (n.d.). Retrieved December 30, 2021, from 

Neutropenia. Cancer.Net. (2019, November 22). Retrieved December 30, 2021, from 

Understanding laboratory tests fact sheet. National Cancer Institute. (n.d.). Retrieved December 30, 2021, from 

U.S. National Library of Medicine. (2020, July 31). Hemoglobin test: Medlineplus medical test. MedlinePlus. Retrieved December 30, 2021, from

This article meets Iris standards for medical accuracy. It has been fact-checked by the Iris Clinical Editorial Board, our team of oncology experts who ensure that the content is evidence based and up to date. The Iris Clinical Editorial Board includes board-certified oncologists and pharmacists, psychologists, advanced practice providers, licensed clinical social workers, oncology-certified nurses, and dietitians.