Blood Tests for Sickle Cell Disease

Regular blood work is an important way to track overall health. It is especially important for people with blood disorders like sickle cell disease (SCD). Blood tests during routine doctor’s visits can give information about the status of the disease and screen for complications.

Some common routine blood tests are complete blood count (CBC) and reticulocyte count, which tell doctors about different types of blood cells. Blood tests for kidney and liver function are also common. These tests are often performed together on a comprehensive metabolic panel of tests that also includes measurements of electrolytes, proteins, and glucose in the blood.1-3

During the test, doctors will draw blood from a needle inserted into a vein in your arm or hand. They will analyze it in a lab and discuss the results with you. Follow your doctor’s instructions about preparing for the test.

What is a complete blood count?

A complete blood count (CBC) is usually performed at every doctor’s visit for people with SCD. It gives doctors information about all 3 types of blood cells: red blood cells, platelets, and white blood cells. SCD mainly affects red blood cells, but can sometimes modify platelets and white blood cells. Some SCD medications also affect blood cells.4,5

People with SCD generally have anemia (fewer red blood cells than normal) because sickled red blood cells do not circulate in the blood as long as normal red blood cells. This leads to lower hemoglobin levels as well. A normal hemoglobin level is around 12 to 15 g/dL. People with SCD have hemoglobin levels of 6 to 11 g/dL.4,5

People with SCD usually have higher levels of white blood cells, especially neutrophils. These are a type of white blood cells that fight bacterial infections. Major increases in white blood cell count may indicate infections. On the other hand, people taking hydroxyurea may have too few neutrophils to fight off infections (neutropenia).4,5

The exact levels of each blood cell depend on the type of SCD and the person. It is important for your doctor to know your normal hemoglobin level. A major change from your normal levels may indicate an acute complication, such as severe anemia.4-6

What is a reticulocyte count?

Reticulocytes are young, immature red blood cells forming in the bone marrow (the soft center of bones). Normally, reticulocytes are only released into the blood after they develop into red blood cells. For most healthy people, the number of reticulocytes in the blood is very low. A normal reticulocyte count is 0.45 to 1.8 percent.5

People with SCD have more reticulocytes in the blood because the body is rapidly making more red blood cells to offset anemia and releasing the reticulocytes early. People with SCD may have a reticulocyte count of 2 to 3 percent or more.5

What tests are done to check kidney function?

Kidney disease is a common complication of SCD. When sickle cells block blood flow to the kidney, it can no longer filter out waste properly.7,8

Children and adults with SCD should get regular blood tests for kidney function. Common blood tests measure the amount of creatinine or blood urea nitrogen (BUN) in your blood. Creatinine is a waste product released directly into the urine by the kidneys. Urea is a waste product formed when proteins are metabolized.9,10

High blood creatinine or BUN levels may mean that your kidneys are not working as well as they should. A BUN-to-creatinine ratio may also be used to diagnose kidney problems.9,10

What blood tests are done to test liver function?

Liver problems are also common for people with SCD. Sickle cells can block blood flow to the liver and prevent it from getting rid of waste. Chronic blood transfusions also increase the risk for liver damage.11

People with SCD should get regular blood and other tests for liver function. Common blood tests measure the amount of bilirubin, aspartate transaminase (AST), and alanine aminotransferase (ALT).12,13

Bilirubin is a yellow pigment produced during the normal breakdown of hemoglobin and is processed by the liver. High bilirubin levels may indicate liver disease, gallstones, or hepatitis, depending on the type of bilirubin. ALT and AST are enzymes in the liver that gets released into the blood when the liver is damaged.12,13

What other blood work do people with sickle cell disease get?

Other blood tests can give doctors information about the status of the disease. For example, some additional tests that doctors commonly perform include:2-3,14-15

  • Tests to diagnose sickle cell disease, such as hemoglobin solubility and hemoglobin electrophoresis (to determine the amount of abnormal hemoglobin in the blood).
  • Type and cross with red blood cell antigen testing in preparation for future blood transfusions (to assure that your body will accept the donor red blood cells).
  • Blood smears to look at abnormal and sickle-shaped red blood cells
    Measurement of iron levels in the blood, which may be high in people receiving chronic blood transfusions.

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Written by: Matthew Zajac | Last reviewed: January 2021