Complete Blood Count (CBC) Test and Sickle Cell Disease 

Sickle cell disease (SCD) is a condition that affects red blood cells. Children with SCD need regular blood tests, such as a complete blood count (CBC) test. A CBC test measures the number and types of blood cells, such as: 

• Red blood cells 
• White blood cells 
• Platelets 

A CBC test also measures hemoglobin and hematocrit levels. Your care provider may order other tests, including: 

• CBC with differential: Gives more information about the different types of white blood cells.  
• Reticulocyte test: Shows how many new red blood cells your child’s body is making.  

Regular blood tests help monitor blood counts and overall health. Results show how sickle cell disease affects your child and how well treatment is working. 

For the test, a health care provider takes a blood sample from your child’s vein. The sample is sent to a lab. The results are usually ready in a few days. 

Learn more about complete blood count tests and sickle cell disease.

What CBC results mean and normal ranges

The report shows your child’s results and a range of numbers called a reference range. These numbers show what is considered normal. Your child’s care provider compares your child’s results to these ranges. Ranges vary based on your child’s age, sex, and other factors.  

Sickle cell disease can cause your child’s lab values to be outside the normal reference range. Review your child’s CBC test results with your care team. They can explain the numbers and what they mean. 

Red blood cell (RBC) count

Normal red blood cells are round and flexible. In sickle cell disease, red blood cells become hard, sticky, and shaped like a banana (sickle-shaped). This makes it hard for them to move through the body. They can also slow or block blood flow. 

Children with SCD commonly have anemia (low red blood cell counts or low hemoglobin) because sickled blood cells break down and do not last as long as healthy red blood cells. 

White blood cell (WBC) count

White blood cells help fight infection. Sickle cell disease may cause inflammation in the body, which can affect white blood cells. 

Illness and some medicines can make your child’s white blood cell count go up or down for a short time. A low white blood cell count increases the risk of infection and can make it harder to recover from illness.  

Platelet count

Platelets are blood cells that help the blood clot and stop bleeding. If your child has a low platelet count, they may bruise or bleed more easily. Children with sickle cell disease often have normal platelet counts. Low platelet levels are not usually caused by sickle cell disease. 

Absolute neutrophil count (ANC)

An absolute neutrophil count (ANC) shows how many neutrophils are in the blood. Neutrophils are white blood cells that fight infection. A low ANC is called neutropenia. If your child has neutropenia, they may get infections more easily and take longer to get better. 

Hemoglobin

Hemoglobin is the protein in red blood cells that carries oxygen to the body’s tissues and organs. People with sickle cell disease have an abnormal kind of hemoglobin called sickle hemoglobin or hemoglobin S. Abnormal hemoglobin S causes red blood cells to: 

• Form a sickle shape 
• Become sticky and stiff 
• Clog the small blood vessels in the body 
• Not last as long as they should 
• Break apart 

It is important to know your child’s hemoglobin levels. This is an important measure of how sickle cell disease is affecting their red blood cells. The numbers will change due to the disease, treatments, and other factors.   

Hematocrit (HCT or PCV)

Hematocrit (HCT), also called packed cell volume (PCV), shows how much of the blood is made up of red blood cells. In sickle cell disease, hematocrit levels may be low since sickle cells break down faster than the body can replace them. 

Mean corpuscular volume (MCV)

The mean corpuscular volume (MCV) shows the average size of red blood cells. This can change based on: 

• Hydroxyurea treatment, which can increase MCV 
• Anemia or other conditions that affect red blood cells 
• How fast red blood cells break down and are replaced 

Reticulocyte count

A reticulocyte count is often ordered along with a CBC test. It measures the number or percentage of young red blood cells (reticulocytes) in the blood. A person with sickle cell disease may have a higher reticulocyte count than normal. This is because their body must make more new red blood cells to replace the sickled cells that do not live as long.  

It is important to get blood tests as recommended. Your care team uses the results to monitor your child’s health and guide treatment.

Questions to ask your care team

• How often will my child need routine blood tests? 
• How will I get my child’s lab results? 
• What CBC results are most important for my child's sickle cell disease? 
• What changes in my child's blood counts should I watch for? 
• How do my child’s medicines affect their lab results? 
• What is my child’s baseline hemoglobin? 
• Are any of the results outside the normal range or the range that you expect for my child? 
• What do my child’s results mean for their current treatment plan? 
• Will my child need additional tests? 

Related content