Myeloproliferative Neoplasms: Common Blood Work Explained

Prior to being diagnosed with a myeloproliferative neoplasm you may rarely need blood work, maybe once a year with your annual physical exam. Now you might wonder—what is all this blood work? What is my doctor looking for? All the blood work that could be possibly ordered is more than we can review here, but let's look at the common ones.

The CBC is one of the most common type of lab work used to monitor blood disorders. The CBC reviews your blood cells: white blood cells, red blood cells, and platelets. This test is often the first clue to what is causing your symptoms, is part of the diagnostic work-up, and may be drawn frequently during treatment.

White blood cells (WBC) are part of your immune system and help fight infections. There are 5 types of WBCs: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. The number of WBCs in your blood is usually the first number reported on the CBC.  Part of the CBC, called the differential or diff, looks at what percentage of each type of WBC is present.

In polycythemia vera (PV) or essential thrombocythemia (ET), your WBC count might be slightly elevated (leukocytosis). In primary myelofibrosis (PMF), some people with have elevated WBC count, some normal, while others will have a low WBC count (leukopenia).

Red blood cells (RBC) carry oxygen from the lungs to the organs. There are several ways to look at the red blood cells on the CBC. First, the RBC count is the number of red blood cells in circulation. Hemoglobin is the protein found in the RBC that carries the oxygen. Hematocrit represents how much of the blood is made up of RBCs (compared to WBC and platelets).

In conditions that cause increased numbers of RBC, like polycythemia vera, the hemoglobin and hematocrit are elevated. The hematocrit is often used to monitor the effectiveness of treatment in PV. Medications and phlebotomy (physical removal of blood) are adjusted based on the desired hematocrit range (typically less than 45 percent in men and less than 42 percent in women).

In PMF, your hemoglobin level is part of the formula used to determine your prognostic score. This may change over the course of your illness. A hemoglobin less than 10 grams per deciliter (g/dL) at baseline, counts as two points in the prognostic score (more points equal higher risk disease). It can also be used to determine if you need a blood transfusion.

Blood transfusions are typically given when the hemoglobin drops below eight grams per deciliter or if you are symptomatic (fatigue, dizziness, elevated heart rate). Requiring transfusions adds an additional point in the prognostic score.

Platelet count is also included in the CBC. Similar to hematocrit in PV, in people with ET requiring treatment, the platelet count is used to adjust treatments based on desired platelet count. In PMF, the platelet count less than 100,000 cells per microliter adds one point to your prognostic score.

ET and PV can evolve into myelofibrosis and leukemia, the early signs of this change may be noted on the CBC, particularly a significant drop in the hemoglobin and platelet count. The red blood cell and platelet become abnormally shaped in myelofibrosis which can be seen on a blood smear (microscope slide of blood cells).

People with ET are at risk of developing acquired von Willebrand disease, a bleeding disorder. This risk goes up as the platelet count goes up (more than one million platelets per microliter). If you have ET and bleeding, a von Willebrand panel may be sent to determine if this is the cause. Treatment is reducing the platelet count.

When you are getting frequent blood work, it can be frustrating and difficult to see the reason. Discuss these concerns with your physician so that you can both be on the same page.