Blood Tests for PNH
When you have anemia caused by the destruction of red blood cells, doctors call this hemolytic anemia. There are several blood tests used to help confirm a diagnosis of PNH by looking for signs of hemolytic anemia. Specific tests include:
- A complete blood count (CBC) to look for signs of low hemoglobin. This test uses a number of methods to measure how many of each blood cell type are in your blood sample.
- An LDH test looks at the level of an enzyme called lactate dehydrogenase. High levels of LDH in the blood can mean that red blood cells are breaking apart (hemolysis) or that there is tissue damage in the body. It is important for patients with PNH to have LDH monitored regularly.
- A bilirubin test measures the total amount of this substance in your blood. High levels may indicate destruction of red blood cells.
- A reticulocyte count measures the number of young red blood cells in your blood. People who have PNH may have elevated reticulocyte counts because their bone marrow is making lots of new red blood cells.
The gold standard for confirming the presence of PNH is a flow cytometry test. This test tells your doctor if any proteins are missing from the surface of blood cells. PNH cells are missing some or all of two proteins on their surface. These proteins are called CD55 and CD59. FLAER is a new type of flow cytometry test that is also used.
Using flow cytometry, your doctor can usually divide your blood cells into 3 types:
- PNH I cells, or Type I cells: These cells are normal. They respond in a healthy way to the complement system.
- PNH II cells, or Type II cells: These cells are partially sensitive to the complement system. They are missing some of the CD55 and CD59 proteins that protect them from attack.
- PNH III cells, or Type III cells: These cells are extremely sensitive to the complement system. Of the 3 groups of cells, these break apart most easily. They are missing all the proteins that protect normal cells from attack. Most people with PNH have Type I and Type III cells, but the amount of each type of cell can vary greatly.
Other Blood Tests
Doctors may ask you do to several types of blood tests to help them understand your case of PNH and create a treatment plan. These include:
- EPO level, also called erythropoietin, measures how much of this protein is being made by your kidneys. EPO is created in response to low oxygen levels in the body, typically caused by low red cell counts and anemia. EPO causes your bone marrow to make more red blood cells. A low EPO level may indicate a problem other than PNH, or it may make anemia worse in people who have PNH.
- Iron level test, also called a ferritin test, checks the level of iron in your blood. If a shortage of iron is causing anemia, it can be easily treated with iron supplements. If you have too much iron in your body this is called iron overload. It can be caused from getting lots of red blood cell transfusions or by genetic conditions. A number of treatments exist to remove iron from your body.
- Vitamin B12 and a folate level may be done to rule out other causes of low red cell counts. If your red blood cells have an abnormal shape, size or look, this can be caused by low levels of vitamin B12 and folate (folic acid). These abnormal looking cells don’t work right, and this can lead to anemia.
Bone Marrow Tests
An examination of your bone marrow is important for the diagnosis of PNH. It is usually a simple 30-minute procedure. First, the doctor uses a hollow needle to remove some bone marrow aspirate (liquid bone marrow), typically from the pelvic or breast bone. A solid piece of bone marrow is also removed for a bone marrow biopsy.
The doctor will look at your liquid bone marrow under a microscope and send a sample of your bone marrow to a lab.
A bone marrow test is done for two main reasons:
- To help confirm a diagnosis of PNH
- To understand how well or poorly your bone marrow is making blood cell
The bone marrow test shows:
- The quantity (cellularity) of your bone marrow occupied by different cells
- Exactly what types and amounts of cells your bone marrow is making
- Increased, decreased, or normal levels of iron in your bone marrow
- Chromosomal (DNA) abnormalities
Learn more about the process of getting a bone marrow test.