Complete blood count (CBC) and differential
CBCs and differentials are the most frequently ordered tests used to help diagnose and monitor MPDs.  Often ordered as part of a yearly physical exam, they are routine tests that count the number and relative proportion 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 MPDs, 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.  CBCs 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.   

With polycythemia vera, increased RBCs, platelets, and sometimes WBCs, may be seen.  A high hematocrit (Hct, the percentage of RBCs in the total blood volume) may indicate relative polycythemia vera (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.  With thrombocythemia, greatly increased number of platelets are seen along with: abnormally large platelets, platelet clumps and fragments of megakaryocytes. 

Irregularities in cell counts may be due to MPDs, 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 MPD.

Bone marrow aspiration/biopsy
If your doctor suspects a bone marrow disorder he may order a bone marrow aspiration or biopsy to collect a small sample of your marrow.  When a specialist (a pathologist, oncologist, or hematologist) examines the bone and fluid from your bone marrow sample under the microscope, he can see the number, size, and shape of your precursor cells (blasts), red and white blood cells, and megakaryocytes (platelet precursors).  He 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 polycythemia vera is suspected.  Low levels oxygen are associated with secondary polycythemia.

Erythropoietin, This is a hormone that stimulates the bone marrow to produce RBCs.  With primary polycythemia, erythropoietin levels will be very low or absent, but with secondary polycythemia 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, changes to the genetic code that are seen in a few cases of MPDs.

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