How is MPN diagnosed?
Myeloproliferative neoplasms are diagnosed by examining samples of your blood and bone marrow. Sometimes the diagnosis of MPN is only made when other causes of altered blood count have been excluded.
Full blood count
The first step in the diagnosis is a simple blood test called a full blood count (FBC) or complete blood count (CBC). This involves a sample of blood from a vein in your arm being sent to the laboratory for investigation. People with polycythaemia vera have a high red cell count, haemoglobin level and haematocrit due to the excessive production of red cells. A raised white cell count (especially a raised neutrophil count) and a raised platelet count are also common findings. Other findings that help confirm the diagnosis of polycythaemia vera is the presence of the JAK2 mutation or other cytogenetic abnormalities in your blood or bone marrow cells.
A persistently raised platelet count is the most common sign of essential thrombocythaemia. Around a third of people with essential thrombocythaemia will also have a mildly raised red cell and/or white cell count.
People with myelofibrosis commonly present with varying degrees of anaemia. When examined under the microscope the red cells are often described as being ‘teardrop-shaped’. Higher than normal numbers of white cells and platelets may be found in the early stages of this disorder, but low white cell and platelet counts are common in more advanced disease.
Bone marrow examination
If the results of your blood tests suggest that you might have MPN, a bone marrow biopsy may be required to help confirm the diagnosis. A bone marrow biopsy involves taking a sample of bone marrow, usually from the back of the hip bone and sending it to the laboratory for examination under the microscope. The bone marrow biopsy may be done in the haematologist’s rooms, clinic or day procedure centre and is usually performed under local anaesthesia with sedation given either by tablet or through a small drip in your arm. The sample of bone marrow is examined in the laboratory to determine the number and type of cells present and the amount of haemopoiesis (blood forming) activity taking place there.
Once the diagnosis of MPN is made, blood and bone marrow cells are examined further using special laboratory tests. These include immunophenotyping and cytogenetic tests. These tests provide more information about the exact type of disease you have, the likely course of your disease and the best way to treat it. Other tests may be conducted to provide information on your general health and how your vital organs are functioning. These include a combination of further blood tests and imaging tests (x-rays, scans and ECG).
These results will provide a baseline of your disease and general health, which will be compared with later results to assess how well you are progressing and responding to treatment.