Q. For a 25 years old female, what is the normal level of G6PD? What is the cut-off value below, which the person is termed as G6PD deficient? If G6PD deficient, what drugs should the person avoid?
Glucose-6-phosphate dehydrogenase (G-6-PD) deficiency is the most common human enzyme deficiency. It is an X-linked inherited (genetic) disease caused by a mutation in the gene producing this enzyme, which primarily affects men. More than 300 reported variants are described in literature.
As the G6PD deficiency is transmitted on the X chromosome, therefore all men with the disease are hemizygous, and most women are heterozygous. Early in the process of female embryonic development, one X chromosome is inactivated in each somatic cell, which results in two cell populations, one with normal G6PD and one with deficient G6PD. In most cases, equal numbers of normal cells and G6PD-deficient cells are produced; however, it is possible to have an imbalance between the two cell populations. The clinical phenotype is determined both by the percentage of G6PD-deficient red cells and by the degree of G6PD activity in the enzyme-deficient cells.
The G6PD enzyme catalyses several biochemical reactions, one of which produces a chemical called glutathione. This compound, in its reduced form, acts as a scavenger for dangerous metabolites produced in the cells. The red blood cells need this enzyme to produce a molecule called NADPH that protects the cells against oxidative stresses. The red blood cells of an individual deficient in G-6-PD, when given oxidative drugs or exposed to oxidative stress, rapidly breakdown (haemolyse) to cause anaemia.
Most patients are asymptomatic. Some patients present with or report a history of jaundice at birth, often requiring exchange transfusion. A history of infection or drug-induced haemolyisis is also common.
A standard reference range is dependent on many factors, including patient age, gender, sample population, and test method and each laboratory must establish its own values depending on the population. By and large the reference values range from 4.6 to 13.5 units/gram of haemoglobin.
Some of the drugs to be avoided include:
Acetanilid antimalarial drugs (primaquine, chloroquine, pamaquine), ciprofloxacin, chemicals (naphthalene in mothballs) chloramphenicol, Doxorubicin methylene blue, nalidixic acid, niridazole, nitrofurantoin, norfloxacin phenazopyridine, Phenylhydrazine Pyridium sulfonamides vitamin K analouges.