Glucose-6-phosphate dehydrogenase (G6PD) enzyme testing is used to screen for and help diagnose G6PD deficiencies. A G6PD deficiency is an inherited disorder that can lead to a certain type of anemia known as hemolytic anemia. G6PD helps red blood cells function normally. It also protects them from potentially harmful by-products that can accumulate when the body is fighting infection, or as the result of certain medications. G6PD protects oxygen-rich red blood cells (RBCs) from chemicals called reactive oxygen, which build up in the body during a fever, infection, or when taking certain medications. If there is an insufficient amount of G6PD, RBCs will not be protected from these chemicals. The blood cells will die, leading to anemia.