Glucose-6-phosphate dehydrogenase

G6PD testing may be ordered on children who experienced persistent jaundice as a newborn that could not be explained by another cause. It may also be ordered on patients of any age who have had one or more unexplained episodes of haemolytic anaemia. If the patient had a recent viral or bacterial illness or was exposed to a known trigger (such as fava beans, a 'sulpha' drug, or naphthalene), followed by a haemolytic episode, then G6PD deficiency may be considered. Repeat G6PD testing may occasionally be ordered to confirm initial findings or if results were normal following an episode of haemolysis; in the most common form seen in persons of African ancestry, the enzyme levels are normal in newly produced cells but fall as red cells age so that only the deficient cells were destroyed.

G6PD testing is primarily performed on patients who have had symptoms of anaemia (such as fatigue, pallor, a rapid heart rate) and/or jaundice. Their laboratory test results may show increased bilirubin concentrations (bulirubinaemia), haemoglobin in the urine (haemoglobinuria), a decreased RBC count, an increased reticulocyte count and sometimes the presence of Heinz bodies inside the RBCs.

G6PD activity testing is ordered on patients in whom other causes of the anaemia and jaundice have been ruled out and is ordered once the acute incident has been resolved. It should not be performed when a patient is having or recovering from a haemolytic episode. This is because the older, more G6PD-deficient RBCs are usually destroyed, leaving younger less deficient RBCs to be tested. This can make the activity level appear closer to normal than it actually is. If testing is done during this time period, it should be repeated at a later time to confirm the G6PD level.

Genetic G6PD testing may sometimes be done within a family to help identify the relevant mutation in female carriers (such as the mother of an affected son or daughter of an affected father) when one or more male family member has a G6PD deficiency.

If there is decreased G6PD level, then the more likely the patient is to experience symptoms when exposed to an oxidative stress. The results, however, cannot be used to predict how an affected patient will react in a given set of circumstances. The severity of symptoms will vary from patient to patient and from episode to episode.

If a male patient has normal G6PD levels, it is likely that he does not have a deficiency. However, if the test was performed during an episode of haemolytic anaemia, it should be repeated a few weeks later when the RBC population has had time to replenish and mature.

Heterozygous females will have both G6PD-deficient and non-deficient cells. They will usually have normal or near normal G6PD levels and few will experience symptoms. A carrier may not be detected through G6PD screening; however, the rare homozygous female will show a significant decrease in G6PD level.

If a G6PD genetic mutation is detected, the patient will likely have some degree of G6PD deficiency. An individual patient may experience symptoms that range from nonexistent to acute and severe to chronic at various times throughout their life. An affected male will pass the mutation on to his daughter, who will be a carrier. A heterozygous/carrier female has a 50% chance of passing it on to each of her children. A homozygous female will pass one of her mutations to all of her children. The mutation(s) will be the same within the family and may be common in a geographic region. [See Genetic testing for more information].

While G6PD deficiency is found throughout the world, it is most common in those of African or Mediterranean descent and is also found in those from Southeast Asia. Its geographical area of increased prevalence mirrors that of malaria. Some researchers think that having a G6PD deficiency has historically offered a survival advantage to those infected with malaria, a parasite that physically invades the RBCs.

Biochemical testing and electrophoresis can be used to distinguish between different G6PD enzyme variants. This has been used in the past to study the prevalence and levels of different types of the enzymes, both normal and deficient, but this testing is used almost exclusively in the research setting.