A blood test and sometimes a bone marrow test are used to diagnose polycythemia vera (PV).
After your doctor takes your blood, he or she sends it to a lab for a complete blood count (CBC), which measures the number of red cells, white cells and platelets in your blood. A PV diagnosis is considered if your red cell counts are elevated. The test also measures your hemoglobin and hematocrit concentration:
Hemoglobin is the iron-containing protein in red cells that carries oxygen from the lungs to the body's tissues. In healthy individuals, hemoglobin concentration ranges from about 120 to 150 grams per liter (g/L) of blood in women and about 140 to 180 g/L in men.
Hematocrit is the proportion of red cells in blood volume, usually expressed as a percentage or an increase in hemoglobin concentration in the blood. Hematocrit concentration ranges from about 36 percent to 46 percent in healthy women and 42 percent to 52 percent in healthy men.
If a PV patient's previously normal hematocrit concentration of 45 percent increases by one-third to 60 percent, the corresponding normal hemoglobin concentration of 150 g/L of blood would also increase by one-third to 200 g/L of blood. The corresponding red cell count would increase by one-third as well. Thus, for diagnostic purposes, any of the three measurements can be used to diagnose PV.
Other Markers in Blood
Your doctor looks for other markers in your blood to confirm a PV diagnosis:
- An elevated white cell count, especially the neutrophil count, a type of white cell. The increased white cell count is mild in most PV patients and usually doesn't progress.
- An elevated platelet count, which occurs in at least half of all patients.
- The presence of the JAK2 gene mutation.
- An elevated red cell mass (usually only measured if the elevated hematocrit or hemoglobin concentration can't confirm a diagnosis).
- Normal or near-normal oxygen saturation in the arteries.
- A low erythropoietin (EPO). Blood levels of the hormone EPO are usually low in PV but normal or high in secondary polycythemia.
Bone Marrow Tests
Your doctor may examine your bone marrow even though the test isn't needed to diagnose PV. If you have PV, your marrow contains more than the normal number of cells and your blood lacks iron because it was used to make additional red cells.
Your doctor can also use your marrow cells to analyze your chromosomes and measure the ability of red cell precursors to grow without added EPO.
Bone marrow testing involves two steps usually performed at the same time in a doctor's office or a hospital:
- a bone marrow aspiration to remove a liquid marrow sample
- a bone marrow biopsy to remove a small amount of bone filled with marrow