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Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency


Evan M. Braunstein

, MD, PhD, Johns Hopkins University School of Medicine

Reviewed/Revised Jul 2022 | Modified Sep 2022

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited genetic disorder that can result in destruction of red blood cells (hemolysis) after an acute illness or use of certain drugs.

  • G6PD deficiency occurs because of a genetic defect in an enzyme involved in red blood cell metabolism.

  • G6PD deficiency results in destruction of red blood cells in response to certain illnesses or drugs.

  • The destruction of red blood cells can cause symptoms, including yellowing of the skin and whites of the eyes, dark urine, and sometimes back or abdominal pain.

  • A blood test can assess the level of the G6PD enzyme.

  • Treatment usually is not needed, but people with G6PD deficiency should avoid certain drugs.

G6PD is an enzyme important for maintaining the stability of hemoglobin. Hemoglobin is the protein contained in red blood cells that enables them to carry oxygen from the lungs and deliver it to all parts of the body. G6PD helps protect hemoglobin from damage due to the stress of infections or the use of certain drugs or substances. People who have G6PD deficiency inherit a defect in the gene responsible for producing G6PD so they do not have enough of the enzyme in their blood cells.

The G6PD deficiency is X-linked X-Linked Inheritance Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body or code for functional RNA molecules.... read more , meaning that mainly males are affected and females are carriers of the defective gene. However, activity of the G6PD gene is highly variable, so in some people G6PD does not work quite as well as it should and in others it does not work at all.

This defect is common in males with African or Black American ancestry. It is also common among people with ancestors from the Mediterranean basin (such as those of Italian, Greek, Arab, and Sephardic Jewish ancestry) and people with ancestors from Asia.

G6PD deficiency shortens red blood cell survival. When people with G6PD deficiency get sick, for example due to a viral or bacterial infection or diabetic ketoacidosis Diabetic Ketoacidosis Diabetic ketoacidosis is an acute complication of diabetes that occurs mostly in type 1 diabetes mellitus. Symptoms of diabetic ketoacidosis include nausea, vomiting, abdominal pain, and a characteristic... read more , their red blood cells rapidly break down. These episodes of red blood cell destruction (hemolytic crisis) usually resolve on their own.

Red blood cell destruction may also occur after exposure to certain drugs. These drugs and substances include primaquine, salicylates, sulfonamides, nitrofurans, phenacetin, naphthalene, some vitamin K derivatives, dapsone, phenazopyridine, nalidixic acid, methylene blue, and, in some cases, fava beans.


In most cases, episodes of red blood cell destruction are mild and do not cause any symptoms. However, when the enzyme deficiency is more severe, symptoms include jaundice Jaundice in Adults In jaundice, the skin and whites of the eyes look yellow. Jaundice occurs when there is too much bilirubin (a yellow pigment) in the blood—a condition called hyperbilirubinemia. (See also Overview... read more Jaundice in Adults (a yellowing of the skin and the whites of the eyes), dark urine, fatigue, and shortness of breath. Some people have back and/or abdominal pain.


  • Blood test of G6PD activity

  • Evaluation of a blood smear

Doctors suspect G6PD deficiency in people who develop jaundice during an infectious illness or after taking a drug that is known to trigger an episode. Blood tests, including examining a blood smear, are done to see if red blood cells are breaking down. If they are, doctors can measure G6PD activity in red blood cells. They measure G6PD activity during blood cell breakdown and then again after it has stopped.

Screening tests for G6PD deficiency can be done on people at risk for the disorder.


  • Supportive care

  • Stop taking drugs or substances that may be causing hemolysis

  • Avoidance of known triggers

Often no treatment is needed, and people just have to wait for their red blood cell numbers to return to normal. If an episode is severe, people may need to be hospitalized to receive treatment, such as oxygen or intravenous fluid. Sometimes blood transfusions Overview of Blood Transfusion A blood transfusion is the transfer of blood or a blood component from one healthy person (a donor) to a sick person (a recipient). Transfusions are given to increase the blood's ability to... read more Overview of Blood Transfusion are needed.

Doctors advise people to stop taking any drug or substance that might have caused the episode of hemolysis and to avoid drugs or substances that are likely to trigger an episode.

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