Medically reviewed by Archana Sharma, DO A mean corpuscular volume (MCV) test is a blood test that measures the size and ...

the soft center where new blood cells grow. It causes your marrow to make too many red blood cells so your blood is too thick. You may be more likely to have clots, a stroke, or a heart attack.

Polycythemia vera (PV) causes your bone marrow to make too many red blood cells. You need these cells to carry oxygen around your body, but too many of them can make your blood thicken and form clots.