Too many red blood cells can make the patient’s blood more viscous (thick) so the blood does not flow efficiently. High platelet counts can contribute to the formation of clots (thrombi). Underlying vascular disease, common in older persons with PV, can increase the risk of clotting complications. The clots may cause serious problems, such as stroke, heart attack, deep vein thrombosis or pulmonary embolism. Blood clots occur in about 30 percent of patients even before the PV diagnosis is made. During the first 10 years after a diagnosis of PV, 40 to 60 percent of untreated PV patients may develop blood clots. 

Some people have few troublesome symptoms and PV may only be discovered when blood counts are done during a periodic health examination. However, people should be aware of the following signs, symptoms, and complications of PV:

• Headaches, excessive sweating, ringing in the ears, visual disturbances, such as blurred vision or blind spots, and dizziness or vertigo (a more severe feeling of motion) may occur.
• Fatigue is common.
• Itchy skin, called “pruritus,” especially after warm baths or showers, occurs in some patients.
• A reddened or purplish appearance of the skin, especially on the palms, ear lobes, nose, and cheeks may occur.
• Some patients may experience a burning sensation in the feet.
• An enlarged spleen could cause abdominal fullness or discomfort, this may be confirmed on physical examination or by ultrasound.
• Angina or congestive heart failure may be a harmful effect of the thicker blood and tendency of platelets to “clump” in the coronary blood vessels and lead to clots called “thrombi.”
• Gout, a painful inflammation of the joints caused by increased levels of uric acid may occur or become worse.
• Bleeding or bruising, usually minor, occurs in about 25 percent of PV patients.

In addition to the signs and symptoms above, people with PV are at slightly greater risk than the general population for developing leukemia as a result of the disease and/or certain drug treatments