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Laboratory tests

Full blood count (FBC) and differential
FBCs and differentials are the most frequently ordered tests used to help diagnose and monitor MPNs. Often ordered as part of a yearly physical examination, they are routine tests that count the number and relative proportion of each of the different types of cells in your blood stream. They give your doctor information about the size, shape and relative maturity of the blood cells present in your blood at that moment.

Typically, the body produces and destroys all cells in a balanced manner, and conditions where a cell type is over – or under-expressed are considered abnormal. In MPNs, if the production of a cell type outpaces its destruction (or vice versa) by the body, the cell count can either increase or decrease. Disease progression changes the elevated and/or decreased numbers of blood cells. FBCs and differentials can be used to detect WBC, RBC and platelet increases, decreases, and abnormalities. They can help determine their severity, diagnose their cause, monitor the course of a disease, and monitor the response to treatment.

In polycythaemia vera, increased RBCs, platelets, and sometimes WBCs, may be seen. A high haematocrit (Hct, the percentage of RBCs in the total blood volume) may indicate relative polycythaemia (caused by a decreased amount of fluid in the blood). With myelofibrosis, immature granulocytes, and misshapen immature teardrop shaped red blood cells are often seen and WBC and RBC numbers are often decreased. In essential thrombocythaemia (ET), greatly increased numbers of platelets are seen along with: abnormally large platelets, platelet clumps and fragments of megakaryocytes.

Irregularities in cell counts may be due to MPNs, but they may also be due to a variety of other temporary or chronic conditions. Other testing is usually done to confirm or rule out the diagnosis of an MPN.

Bone marrow aspiration/biopsy
If your doctor suspects a bone marrow disorder, they may order a bone marrow aspiration and biopsy to collect a small sample of marrow. When a specialist (a pathologist, oncologist or haematologist) examines the bone and fluid from the bone marrow sample under the microscope, they can see the number, size and shape of precursor cells (blasts), red and white blood cells, and megakaryocytes (platelet precursors). They can determine the proportions of mature and immature cells, see any overgrowth of fibrous tissue, and detect any cancer cells from cancers that may have spread to the marrow. Most bone marrow disorders can be diagnosed during this examination.

For more detail on this test, see bone marrow aspiration and biopsy.

Other testing that is sometimes done includes:

ABGs (arterial blood gases) - This test measures the amount of gases in your arterial blood and may be done when polycythaemia vera is suspected. Low levels of oxygen are associated with secondary polycythaemia.

Erythropoietin is a hormone that stimulates the bone marrow to produce RBCs. With primary polycythaemia, erythropoietin levels will be very low or absent, but with secondary polycythaemia they will be normal or high.

Genetic testing is sometimes used to check for the presence or absence of a Philadelphia (Ph') chromosome or a BCR-ABL translocation, and the JAK2V617F mutation. These can be performed on both peripheral blood and bone marrow tissue.

Non-laboratory tests

X-rays and other imaging scans are sometimes used to look for signs of disease such as masses of cells in the chest, spleen or liver.

Last Review Date: January 13, 2020