Many patients with Polycythemia vera may not know they have the disease for some time. Initial symptoms may come and go, or be vague enough to not pinpoint to any one problem until the disease progresses.
Some many initially present with a headache, fever, itchy/warm/red skin, dizziness, etc. Some patients may have an obvious abdominal bulge due to splenomegaly.
As part of any workup, the doctor will almost always order a CBC (Complete Blood Count). Since Polycythemia vera's hallmark is the presence of an increased Red Blood Cell mass, a CBC would be an excellent tool in aiding in the diagnosis of PV. For men, a Hemoglobin concentration of greater than 16.5 g/dL, a hematocrit above 50%, and an increased total Red Blood Cell count would be highly indicative for disease. For women, normal hemoglobin and hematocrit levels are slightly lower than men so roughly 16g/dL and 48% hematocrit could potentially raise alarm. If the doctor can rule out secondary reasons for these being increased, such as dehydration, these numbers would be a cause for your doctor to potentially follow closer to a Polycythemia vera diagnosis. Results far above the previously mentioned numbers would likely aid in diagnosis. Numbers that high but borderline normal, may need more probing. Presenting with any of the symptoms listed here would likely aid in diagnosis. Many instances of increased Hemoglobin/Red Cells/Hematocrit are not due to Polycythemia vera, but to secondary processes.
Your doctor may want to test for mutations within the Janus Kinase 2 (JAK2) gene. As previously mentioned, this gene is responsible for creating a protein that is involved in cell signaling. It tells the bone marrow to "start" or "stop" the creation of new blood cells. A very common mutation "JAK2(V617F)" is found in the overwhelming majority of patients with Polycythemia vera. A laboratory can test your blood and search for this mutation within the gene. It is also possible for the laboratories to search for other metalations within the gene if testing comes up negative for the JAK2(V617F) mutation allele.
Erythropoietin -- a hormone that signals for the body to create more red blood cells. Patients with PV will generally have very low levels of EPO, given that EPO works off a feedback loop, if red cells and tissue oxygenation are abundant there's no need for more EPO to be created. Patients with high RBC/Hemoglobin(Hgb)/Hematocrit(Hct) counts suffering from dehydration, COPD, sleep apnea, etc., will not have these severely low levels. Your doctor may use JAK2 mutation in conjunction with EPO testing to be sure.
Bone Marrow Biopsy -- your doctor may recommend a bone marrow biopsy and/or bone marrow aspirate. A needle is inserted in the bone, generally through the area of the Iliac Crest on the hip. This is the most common and safest site for biopsy due to its location away from major organs and blood vessels. The aspirate portion of the procedure involves removing some of the fluid portion of the marrow itself for examination. Slides will generally be made from this to be viewed microscopically. During the same procedure, a piece of solid bone marrow may be removed for analysis. The end results would generally show a bone marrow with far too many Red Blood Cells being created at a given time.