Anemia is a medical condition where a person suffers a deficiency in red blood cells. The outcome is a reduced availability of blood to transfer oxygen to the tissues of the body.
Before discovering that Spock had been split into two separate beings (one Vulcan, one Human), Dr. Leonard McCoy believed that Spock was suffering from anemia and demanded to perform a medical examination on Spock at once. (TOS short story: "Ni Var")
Many QuchHa' Klingons suffered from anemia, including the Albino. (ST novel: Excelsior: Forged in Fire)