Glucose-6-phosphate dehydrogenase (G6PD) Test

The glucose-6-phosphate dehydrogenase (G6PD) test, also known as the G6PD deficiency test, glucose-6-phosphate dehydrogenase test, G-6-PD test, or RBC G6PD test, is a blood test that checks how much or how active the G6PD enzyme is in red blood cells.

G6PD is a protein that helps protect red blood cells from damage and keeps them functioning normally. Red blood cells carry oxygen from the lungs to tissues all over the body. G6PD function helps these cells withstand damage from certain medicines, infections, foods, and other substances that can stress them. The test is primarily used to identify G6PD deficiency, an inherited condition in which the body has lower-than-normal G6PD enzyme activity.

Low G6PD levels can make red blood cells more prone to early breakdown, a process known as haemolysis (destruction of red blood cells). This can lead to conditions such as acute haemolytic anaemia (sudden destruction of red blood cells), chronic haemolysis (ongoing breakdown of red blood cells), or neonatal hyperbilirubinaemia (high bilirubin levels that may cause jaundice, or yellowing of the skin and eyes, in newborn babies).

The test helps doctors determine whether reduced G6PD activity is contributing to red blood cell destruction and related complications.

The doctor may recommend this test if a person has G6PD deficiency symptoms, such as:

• Fatigue or unusual tiredness
• Pale skin or jaundice (yellowing of the skin and eyes)
• Rapid heartbeat
• Shortness of breath
• Dark or yellow-orange urine

Some people may also need this test because they are more likely to have G6PD deficiency or related red blood cell disorders. These include:

• Newborn babies with jaundice that persists beyond two weeks or cannot be explained by another condition.
• Newborns with a family history of G6PD deficiency.
• Children or adults who experience unexplained episodes of red blood cell destruction (haemolysis).
• People who develop haemolysis after certain infections, medications, or consumption of fava beans (also called broad beans).
• People who have family members with inherited haemolytic anaemia or G6PD deficiency.
• People from African, Asian, Mediterranean, or Middle Eastern backgrounds are more likely to have G6PD deficiency because it is more common in these populations.
• Female relatives of affected individuals who may be carriers of the G6PD gene mutation.

The G6PD test is not usually performed as part of routine health check-ups. It is typically recommended when a doctor suspects G6PD deficiency or needs to investigate why the red blood cells are being destroyed. The frequency of testing depends on the reason for the test, as given in the table below:

A G6PD test can help doctors diagnose or investigate conditions related to reduced G6PD enzyme activity and increased red blood cell damage, such as:

• G6PD deficiency: An inherited genetic condition in which the body has lower-than-normal G6PD enzyme activity, making red blood cells more vulnerable to damage.
• Acute haemolytic anaemia: A condition involving sudden destruction of red blood cells that may occur after exposure to certain infections, medicines, or fava beans in people with G6PD deficiency.
• Chronic haemolysis: Ongoing breakdown of red blood cells that can occur in some severe forms of G6PD deficiency.
• Neonatal hyperbilirubinaemia: High bilirubin levels in newborn babies that may cause jaundice and can be associated with G6PD deficiency.
• Inherited haemolytic anaemias: The test may be used as part of the investigation of inherited conditions that cause premature destruction of red blood cells.
• G6PD carrier status: Additional testing may help identify women who carry a G6PD gene mutation that may be passed on to their children.

What to Expect Before the Glucose-6-phosphate dehydrogenase (G6PD) Test

No fasting is required for a standalone Glucose-6-phosphate dehydrogenase (G6PD) test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise Glucose-6-phosphate dehydrogenase (G6PD) levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the Glucose-6-phosphate dehydrogenase (G6PD) Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

This test measures one important parameter:

• Glucose-6-phosphate dehydrogenase (G6PD) enzyme activity: Measures the level or activity of this enzyme found in red blood cells that helps protect them from damage and supports their normal function.

The G6PD level is measured in units per gram of haemoglobin (U/g Hb). This shows how active the glucose-6-phosphate dehydrogenase enzyme is in red blood cells.

The G6PD normal range​ is given in the table below:

The G6PD test result is interpreted by comparing the G6PD enzyme activity with the laboratory reference range provided in the test report.

Note: In some cases, test results may appear normal if the test is performed soon after an episode of red blood cell breakdown. Your doctor may consider further evaluation if G6PD deficiency is still suspected.

The G6PD test is safe, but like any blood test, it has minor risks and important limitations.

Possible Risks of the Test

Some people may feel mild pain or a slight prick when the needle is inserted, and a small bruise may appear at the site after the test. These effects are usually minor and go away on their own within a short time.

Limitations of the Glucose-6-Phosphate Dehydrogenase (G6PD) Test:

• The test result may appear normal if it is done during or soon after a haemolytic episode, because the red blood cells most affected by G6PD deficiency may already be destroyed.
• A recent blood transfusion can affect test results because donor red blood cells might mask the patient’s actual enzyme level.
• A large number of young red blood cells (reticulocytes) after haemolysis can temporarily increase enzyme activity and hide a deficiency.
• Severe infections or other conditions that rapidly change red blood cell turnover can affect test accuracy.
• Very high white blood cell counts may sometimes interfere with results, falsely increasing measured enzyme activity.

Doctors may advise the following tests, along with the G6PD blood test, to help assess red blood cell health and related conditions:

• Blood film examination
• Full blood count (FBC)
• Bilirubin test