Polycythemia vera (PV) is a rare bone marrow disorder that causes your body to produce too many red blood cells. Red cells carry oxygen to the body’s tissues, so it may be hard to imagine how having too many of them could be a bad thing. Many of these new red cells function poorly. On top of that, an overabundance of red cells thickens the blood and makes blood flow sluggish. Thick blood can’t travel through tiny capillaries easily, nor can it reach the small arteries that serve the fingers - or the heart. If your blood can’t easily reach certain tissues, they might die from oxygen deprivation. Fortunately, many people who obtain treatment for PV go on to live full, active lives. And there’s good reason to follow your treatment plan carefully: left untreated, polycythemia vera can cause a host of complications, ranging from clotting problems to leukemia. Let’s look at the major disorders associated with untreated PV. Blood Clots As you might imagine, thick blood clots more easily than blood of a normal density. And because thick blood doesn’t flow easily through the bloodstream, it can stagnate in the veins of the leg and cause a deep venous thrombosis (DTV). Blood clots are dangerous when they break apart or become dislodged from the vein and travel throughout your body. Clots that make their way to the lungs become pulmonary emboli, which can be deadly because they can block the arteries going to your lungs and make it impossible for your blood to transport oxygen to the rest of your body. If a blood clot travels to the brain, it can cause a stroke - another potentially life-threatening complication. Enlarged Spleen Your spleen plays an important role in your body. It stores red blood cells and reprocesses iron. It also filters damaged and defunct red cells from your bloodstream. If your blood becomes clogged with red cells due to polycythemia vera, the spleen has to work extra hard to filter all those extra cells. To cope with this added demand the spleen becomes enlarged, which is called splenomegaly. An enlarged spleen can put pressure on other organs, including the liver, and is more susceptible to infection and to rupture. Heart Failure The thick blood associated with polycythemia vera can’t travel well through tiny arteries, including those that deliver oxygen to the heart tissue. If left untreated, PV can cause chronic oxygen deprivation to the heart. Without a vital supply of oxygen the heart muscle wears out, which leads to heart failure. Chest pain (angina) is a common complication of PV and indicates a lack of oxygen reaching the heart muscle. Myelofibrosis If you think of the blood marrow as a red cell factory, you can picture the way PV kicks production into overdrive and forces the factory to run at high speed over a long period of time. This excessive workload can cause bone marrow cells to die and turn into scar tissue - a condition called myelofibrosis. Myelofibrosis carries serious side effects, including anemia, splenomegaly and an enlarged liver. Sometimes myelofibrosis leads to a form of blood cancer called acute myeloid leukemia (AML). This life-threatening disease often progresses rapidly. The potential complications of polycythemia vera can be severe, indeed, which is why it’s so important to obtain treatment early and follow your treatment plan for life. As a chronic condition, PV needs long-term management. The good news is many people with PV who take their medications and stick to the plan go on to live full lives without experiencing any of these serious complications from the disorder.