GLUCOSE-6-PHOSPHATE DEHYDROGENASE DEFICIENCY Practical IBL
CASE HISTORY A 14 years old boy was admitted to King Abdulaziz University Hospital complaining of headache, anorexia, nausea, and a severe backache. He had bouts of shivering, a temperature of 40.6C. Malaria was suspected and confirmed by identification of the parasite in blood smear. The patient was treated by primaquine. Three days later the patient said that the urine was dark, and the following day it was almost black. He complained of weakness and abdominal and back pain. His sclerae were yellow. The treating doctor requested the following laboratory investigations on admission and 10 days later:
On admission 10 days later Normal range Hemoglobin, g/dl 9.2 14.5 14 - 18 Red blood cells 1012/l 3.5 5 Reticulocytes, % 12 4 0.5 - 1.5 Bilirubin, mol/l 340 23 2 - 14 Red cell glucose-6-phosphate dehydrogenase, units per gram hemoglobin ? 13 - 19
QUESTIONS Determine red cell glucose-6-phosphate dehydrogenase activity in units/gm Hb. What is the cause of changes in the laboratory findings? What is your diagnosis for such a case? What are the functions of glucose-6-phosphate dehydrogenase in different tissues? What are the chemical characteristics of drugs which would be expected to bring on a hemolytic crisis? From your knowledge in vitamins how could you treat this case?
Peroxidation of RBC membrane lipid →↑↑ membrane fragility → Hemolysis Met-Hb The function G6PD in the red cell is to generate NADPH → reduced glutathione → protect the RBCs from the oxidative damage by H2O2
Glucose-6-phosphate dehydrogenase deficiency The disorder is X-linked and women are affected only if homozygous for the condition. G6PD deficiency does not cause any symptoms unless the patient takes one of a number of drugs, such as the anti-malarial primaquine. The administration of one of these grugs causes rapid and often severe hemolysis and jaundice.
Glucose-6-phosphate dehydrogenase deficiency (cont..,) In G6PD deficiency the red cells are not completely lacking in the enzyme; younger cells contain some 6% of the normal amount. This is sufficient to provide reducing power for every day needs When, however, a drug such as primaquine is given the limited reducing power is overwhelmed, oxidation of intracellular proteins takes place and hemolysis, particularly of the older red cells, follows
Measurement of G6PD activity SAMPLE: Blood collected in heparin, citrate or EDTA, Avoid hemolysis T1 (on admission) T10 (at 10 days) Reagent 1 (buffer) 1 ml Reagent 2 (coenzyme) 2.5 ml Hemolysate (sample) Reagent 3 (substrate) Mix & incubate for 10 min. at 37 0C Read the absorbance (A) of each tube at 710 nm against water
CALCULATION G6PD U/g Hb on admission (T1) (Hb) (incubation = Absorbance of T1 X 1015.9 X 1 X 1 9.2 10 (Hb) (incubation time) G6PD U/g Hb at 10 days (T10) = Absorbance of T10 X 1015.9 X 1 X 1 14.5 10 (Hb) (incubation
Normal level of G6PD = 13-19 U/g Hb Your result on admission = U/g Hb Your result at 10 days = U/g Hb Comment on your results: G6PD deficiency