Which term describes an abnormal increase in the number of red blood cells?

• A. Anemia
• B. Leukopenia
• C. Thrombocytopenia
• D. Erythrocytosis

Answer: (D)

An abnormal increase in the number of red blood cells is called erythrocytosis. Red blood cells carry oxygen, so when their numbers rise, the hematocrit increases and the blood can become more viscous, which can raise the risk of headaches and thrombosis. Erythrocytosis specifically describes an actual rise in red cell mass (absolute erythrocytosis), or a relative rise when plasma volume decreases. This contrasts with conditions that describe deficits in other blood cell lines: anemia indicates too few red blood cells, leukopenia indicates too few white blood cells, and thrombocytopenia indicates too few platelets. In clinical terminology, erythrocytosis is the label for having too many red blood cells.