Glucose-6-phosphate Dehydrogenase deficiency (G6PD deficiency)

Glucose-6-phosphate dehydrogenase deficiency (G6PD)

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.

Precautions for Glucose-6-phosphate dehydrogenase (G6PD) deficiency

1. Raised level of reticulocytes may give false high G6PD.
2. G6PD may be in the normal range after the hemolytic episode for the first 6 to 8 weeks.
3. Repeat the test when the anemia is recovered.

Definition of Glucose-6-phosphate dehydrogenase deficiency (G6PD)

1. G6PD is a sex-linked (X-linked) disorder. This is a recessive trait carried on the female (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 and the disease is severe.
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.
      

      G-6-PD role in the stability of the RBC membrane

      

      G-6-PD deficiency mechanism

Glucose-6-phosphate dehydrogenase deficiency (G6PD) distribution:

1. This is common in some ethnic groups of African-American men. About 11% of African-American males are affected.
2. To a lesser extent in people whose ancestors came from the Mediterranean countries like Italy, Greece, or turkey.
3. It is also seen in some areas of India.
4. It is also seen in the Jewish population.
5. 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.
6. Hemolytic crises are associated with the formation of Heinz bodies in Peripheral blood RBCs.
   

   G6PD role in the carbohydrate metabolism

Pathogenesis of Glucose-6-phosphate dehydrogenase enzyme:

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

   G6PD leading to hemolysis of RBCs

The principle and role of the G-6-PD enzyme:

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

   G6PD role for protection of the RBCs

Classification of the G6PD :

1. African-Americans where 10% to 15 % of this population is affected.
2. The Mediterranean is 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.
4. Another classification divides G6PD deficiency into 5 classes.
   1. Class 1: <5% of the normal RBC enzyme activity.
      1. It is rare, chronic, congenital nonspherocytic hemolytic anemia initiated by oxidant medications.
      2. It may be initiated by the fever.
      3. There is no improvement by splenectomy.
   2. Class 2: <10% of normal RBC enzyme activity.
      1. It is seen in 90% of the cases.
      2. There are acute episodic hemolytic crises induced by oxidant drugs like sulfonamide, primaquine, and acetanilid.
      3. This reaction may take place by acidosis.
      4. There is no improvement by splenectomy.
   3. Class 3: 10% to 60% of normal RBC enzyme activity,
      1. It is seen in 90% of the cases.
      2. The hemolytic episode in people without the known hematological disease.
      3. Oxidant drugs or infection (hepatitis, or pneumonia) induce acute self-limiting episodes of hemolysis lasting for 2 to 3 days.
      4. It is also seen in hepatic coma, myocardial infarction, hyperthyroidism, chronic blood loss, and megaloblastic anemia.
   4. Class 4 and 5: These do not show any clinical findings.
5. 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.

Clinical presentation of G6PD Deficiency:

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 Asia and the Mediterranean.
6. In the newborn G6PD deficiency:
   1. Newborn develops neonatal jaundice after the first 24 hours in contrast to the erythroblastosis fetalis.
   2. There are raised serum bilirubin level, that reaches a peak at the 3rd to 5th day.
      1. Serum bilirubin level may reach >20 mg/dL.
   3. In Asian and Mediterranean newborns, neonatal jaundice and kernicterus are more common.

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 of Glucose 6-phosphate dehydrogenase

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 the case of splenectomy.
      2. Heinz bodies are oxidized denatured hemoglobin.
      3. Heinz’s body can be seen by the supravital stain (new methylene blue), in the early stage of hemolysis.
         

         Glucose-6-phosphate dehydrogenase (G6PD) deficiency blood picture

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.
5. After a single dose of primaquine in adults, Intravascular hemolysis takes place and show the following lab findings:
   1. Hct is decreased. It starts in 2 to 4 days and the peak is 8 to 12 days.
   2. Heinz’s body is seen on the peripheral blood smear.
   3. Increased serum bilirubin level was seen in the first few days of hemolysis.
   4. There is reticulocytosis which starts at about the 5th day of hemolysis and the maximum level is at 10 to 20 days.
   5. Hemolysis will subside spontaneously even if primaquine tablets are continued.
   6. Diagnosis is confirmed by the RBC assay of G6PD (by fluorescence technique).

Glucose 6-phosphate dehydrogenase (G6PD) enzyme decreased in:

1. G6PD deficiency.
2. Congenital nonspherocytic anemia.
3. Non-immunologic hemolytic anemia of the newborn.
4. African-American males around 13%.
5. African females are 3% and carrier rate around 20%.
6. It is also seen in Greek, Sardinians, and Sephardic jews.
7. All persons with favism.

Glucose 6-phosphate dehydrogenase (G6PD) enzyme increased in:

1. Megaloblastic anemia (untreated).
2. Thrombocytopenic purpura (ITP = Werlhof disease). These patients become normal after splenectomy.
3. Hyperthyroidism.
4. Viral hepatitis.
5. Myocardial infarction.

Drugs initiating hemolysis due to Glucose 6-phosphate dehydrogenase enzyme (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. 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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