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What is a Glucose-6-Phosphate Dehydrogenase (G6PD) test?

Glucose-6-Phosphate Dehydrogenase or G6PD is an enzyme involved in the production of energy in the body. Any deficiency in the enzyme increases the chances of haemolysis (rupture of RBCs).

It is the most common enzyme deficiency worldwide, with almost 400 million people affected. It generally affects the male population.

If you have a moderate G6PD deficiency, you will be asymptomatic, but some conditions mentioned below can increase the rate of haemolysis (breaking down of RBCs):

  • Bacterial infections
  • Viral infections
  • Antibiotics
  • Antimalarial medicines, 
  • Fava beans consumption or inhalation of pollen from a fava plant (a condition known as favism) 
  • Sulpha medicines.

A G6PD test is done to check for deficiency of the enzyme. It may be done as a:

  • Qualitative test: A screening test that can determine the presence of G6PD in the cell
  • Quantitative test: A confirmation test is a quantitative test done to measure the exact amount of the enzyme activity in the body.

This test is also known as RBC G6PD test or G6PD screen. A repeat G6PD test is usually needed to confirm the initial findings.

  1. Why is a G6PD test performed?
  2. How do you prepare for a G6PD test?
  3. How is a G6PD test performed?
  4. What do G6PD test results indicate?

A healthcare provider orders this test if he/she suspects a G6PD deficiency in a person. It means there is not enough G6PD activity in the body. A G6PD deficiency can increase the rate of haemolysis in the body. It is known as a haemolytic episode.

A haemolytic episode can be caused by certain foods, medicines or infections including:

  • Drugs used to reduce fever
  • Nitrofurantoin
  • Phenacetin
  • Primaquine
  • Sulphonamides
  • Thiazide diuretics
  • Tolbutamide
  • Quinidine

Some signs and symptoms of RBC destruction include:

This test is also recommended if other causes of anaemia and jaundice are negated.

No special preparation is needed for this test. However, you should inform your healthcare provider about your current medications (including prescriptions and nutritional supplements), as certain drugs can alter the results of this test.

Do not undergo this test after a blood transfusion, as it can also affect results.

Do inform your doctor if you have taken any sulfa medicines recently, such as antibacterial or antifungal drugs, anticonvulsants and diuretics or water pills. Adverse reactions are caused by sulfa drugs.

Fasting before the test is not required.

A lab. technician will clean the site of blood collection, ie, your arm and insert a needle into a vein to draw a blood sample.

Later, the collected blood is sent to the laboratory for further analysis.

Some people feel lightheaded after the test or notice a bruise at the injection site, though both these symptoms fade away on their own.

Test results may vary according to the age, gender, the method use or health history. You'll have to ask your healthcare provider for the correct interpretation of the results.

Normal results: The normal range for G6PD is 5.5-20.5 units/gram of haemoglobin. Any value within this range indicates that there is no G6PD deficiency in blood cells.

Abnormal results: It is an indicator of G6PD deficiency. A level less than 10% of the normal range signifies severe deficiency and chronic haemolytic anaemia.

Moderate deficiency can be seen with levels 10-60% less than the normal range. It can be due to the presence of intermittent haemolytic anaemia, which is caused due to certain infections or medications.

Women who are carriers (having a normal gene and a mutated gene) have two forms of RBCs: one with G6PD deficiency and the other with no G6PD deficiency. These women will rarely experience any symptom. However, they will have significantly low G6PD levels, which may not be identified through a G6PD screen test but through a G6PD confirmation test.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. University of Rochester Medical Center. Glucose-6-Phosphate Dehydrogenase. Rochester, New York [internet].
  2. Lab tests online. G6PD. American Association for Clinical Chemistry [internet].
  3. Russell La Fayette Cecil, Lee Goldman, Andrew I. Schafer. Goldman's Cecil Medicine. Elsevier Health Sciences, 2012
  4. Frank JE. Diagnosis and management of G6PD deficiency. Am Fam Physician. 2005 Oct 1;72(7):1277-82. PMID: 16225031
  5. Akram Jamshidzadeh et.al. Protective Effect of Quercetin on Oxidative Stress in Glucose-6-Phosphate Dehydrogenase-Deficient Erythrocytes in Vitro. Iran J Pharm Res. 2010 Spring; 9(2): 169–175. PMID: 24363724
  6. Kahn M et.al. Recombinant human G6PD for quality control and quality assurance of novel point-of-care diagnostics for G6PD deficiency.. PLoS One. 2017 May 26;12(5):e0177885. PMID: 28552983
  7. Genetic home reference. What are the different ways in which a genetic condition can be inherited?. USA.gov U.S. Department of Health & Human Services [internet].
  8. Pranav Sikka. Blue cures blue but be cautious. J Pharm Bioallied Sci. 2011 Oct-Dec; 3(4): 543–545. PMID: 22219589
  9. Johns Hopkins Medicine [Internet]. The Johns Hopkins University, The Johns Hopkins Hospital, and Johns Hopkins Health System; G6PD (Glucose-6-Phosphate Dehydrogenase) Deficiency