Glucose-6-phosphate Dehydrogenase deficiency (G6PD deficiency)

Sample

1. Take blood in EDTA or heparin.
2. Avoid hemolysis.
3. Don’t use oxalate or fluoride in the blood.
4. It is stable for more than 20 days at 4 °C and 5 days at 25 °C.
5. Collect blood in a colored bottle.

Purpose of the test (Indication)

• This test is advised to rule out the deficiency of G6PD in a patient who develops hemolytic anemia after taking drugs or food.

Pathophysiology

1. G6PD is a sex-linked disorder. This is a recessive trait carried on the X chromosome.
   1. The chromosome affected gene is Xq28.
   2. It consists of 515 amino acids and a molecular weight of 59 kDa.
   3. Affected males inherited this gene from their mothers who are usually asymptomatic.
2. If the female has both X gene defective then the disease is very severe.
   1. So female acts as a carrier of this disease with one defective X chromosome.
3. This is common in some ethnic groups of African American men.
4. The condition is commonly asymptomatic but there may be acute hemolysis crises after taking some drugs, ingestion of fava beans, and viral or bacterial infections.
5. Hemolytic crises are associated with the formation of Heinz bodies in Peripheral blood RBCs.
   

   G6PD enzyme and its role in RBC metabolism

6. Pathogenesis:

7. This is detected by an enzyme deficiency in the RBC.
   1. Screening should be done after several days of the crises when the patient is no longer jaundiced.
8. This is an RBC  G6PD enzyme defect. Most patients are asymptomatic with normal Hb and blood smear. They are susceptible to oxidative crises precipitated by drugs (e.g. Dapsones, sulphonamides, antimalarial, aspirin, phenacetin, and nitrofurantoin ), and exposure to fava beans.
9. G6PD deficiency causes precipitation of hemoglobin and cellular membrane changes in RBCs and this may lead to hemolysis.

10. The principle of G-6-P-D deficiency:
    1. This enzyme is needed for the integrity of the Red blood cell membrane.
    2. 30% or less of the deficiency of the G6PD enzyme leads to hemolysis when exposed to some of the drugs, like antimalarial (primaquine) medicines.

11. G6PD is an enzyme used in glucose metabolism.
12. NADPH generated is a necessary ingredient for the enzyme system in the red blood cells to prevent the formation of methemoglobin.

13. Types of G6PD :
    1. African-Americans where 10 to 15 % of this population is affected.
    2. The Mediterranean, more common in Iraqis, Kurds, Sephardic Jews, and Lebanese. This is less common in Greeks, Turks, and North Africans.
    3. MAHIDOL variant is common in southeast Asia where 22 % are males.
14. Variants of G6PD are based on electrophoretic pattern and kinetic criteria:
    1. G6PD A is common in blacks.
    2. G6PD Mediterranean is common in Kurds, Iraqis, Lebanese, Sephardic Jews, and less common in Greeks, Turks, Italians, Portuguese, Ashkenazi Jews, North Africans, and Spaniards.
    3. G6PD Mahidol is common in south-east Asians.
15. Deficiency causes:
    1. These patients may be asymptomatic.
    2. Acute hemolytic anemia due to some drugs, foods, and infection.
       1. The anemia may be self-limiting as there is replacement by the new RBCs formation.
    3. There may be hemoglobinuria.
    4. There may be neonatal jaundice.
    5. Deficiency may be the cause of hemolytic disease of the newborn, in Asian and the Mediterranean.

Normal

1. G6PD screening test = G6PD detected.
2. In the deficiency of G6PD screening test is negative
   1. Adult = 8.6 to 18.6 U/g Hb.
   2. Children = 6.4 to15.6 U/g  Hb.
   3. Conversion of U/g Hb to U/mL of RBC:
      1. U/g Hb X0.34 = U/mL of RBCs.

Diagnosis

1. G6PD deficiency can be diagnosed by :
   1. Screening test by direct enzyme assay on red blood cells.
   2. During crises, peripheral blood smear shows fragmented RBCs like bite cells and blister cells.
      1. Heinz bodies may be seen in the reticulocytes in case of splenectomy.
      2. Heinz bodies are oxidized denatured hemoglobin.
2. Quantitative spectrophotometry.
3. Rapid fluorescent spot test which detects the generation of NADPH from NADP. This test is read under ultraviolet light.
4. Recently DNA analysis is introduced to diagnose variation in G6PD.

G6PD decreased in:

1. G6PD deficiency.
2. congenital nonspherocytic anemia.
3. Non-immunologic hemolytic anemia of the newborn.

G6PD increased in:

1. Megaloblastic anemia (untreated).
2. Thrombocytopenic purpura.
3. Hyperthyroidism.
4. Viral hepatitis.
5. Myocardial infarction.

Drugs initiating hemolysis due to  G6PD deficiency are:

1. Antimalarial.
2. ascorbic acid.
3. Aspirin.
4. Dapsone.
5. Nalidixic acid.
6. Phenacetin.
7. Quinidine.
8. Sulphonamides.
9. Thiazide diuretics.
10. Tolbutamide.
11. Vit.K.
12. Primaquine.
13. Nitrofurantoin.
14. Dapsone.
15. Acetanilide.
16. Antipyretics.
17. Sulfa drugs and sulphonamides.

Treatment

1.  Avoid offending drugs.
2. Treat the underlying infections.
3. Keep a high urine output.
4. Give blood transfusion in case of anemia.
5. The newborn babies with G6PD deficiency are prone to get neonatal jaundice.
   1. In such cases, phototherapy and exchange blood transfusion may be needed.

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