Pyruvate kinase (PK) is an enzyme that helps in the conversion of glucose to energy when there is not adequate oxygen (termed anaerobic metabolism ). This enzyme is located within red blood cells, and if it is deficient, red bloods cells break down more rapidly than usual ( hemolysis ). This can result in a decrease in the number of oxygen-carrying red blood cells in the blood (also known as hemolytic anemia ). This test determines whether there is an abnormally low level of the pyruvate kinase enzyme.