Glucose -6-Phosphate Dehdrogenase

This test measures the amount of G6PD in the red blood cells (RBCs). G6PD is an  enzyme that protects red blood cells from the effects of oxidation. If there is insufficient G6PD, the RBCs become more vulnerable to oxidative damage. If these RBCs are exposed to an oxidative agent (for a list, click here), it changes their cellular structure, precipitating solid lumps of haemoglobin inside the cells (Heinz Bodies), causing the red cells to break up (”haemolyse”).

G6PD deficiency (one of the most severe forms is called Favism – people with this variant are at risk if they eat broad - “fava” - beans) is the most common enzyme deficiency in the world, affecting about 400 million people. It may be seen in up to 20% of the population in Africa, 4-30% in the Mediterranean, and in Southeast Asians. Mutations or changes in the G6PD gene may lead to the production of a G6PD enzyme that has reduced performance or stability. This is expressed as decreased enzyme activity levels.

So far, more than 440 G6PD gene variations have been found and can cause enzyme activity deficiencies of varying severity depending on the particular mutation and on the individual person. The G6PD gene is located on the X chromosome. Since males have one X and one Y chromosomes, a single X chromosome carrying the faulty G6PD gene with no additional healthy X chromosome will result in G6PD deficiency. Females have two X chromosomes, thus two copies of the G6PD gene could possibly be inherited.  Heterozygous females (those with only one altered gene) can produce enough normal G6PD that they usually do not experience any symptoms. However, the presence of the abnormal form may be identified if the deficiency is detected in their male children. Rarely, a female may be homozygous, having two altered G6PD genes (the same or different mutations), and thus will experience G6PD deficiency.

In newborns, G6PD deficiency may cause long term and unexplained  jaundice. Left untreated, this jaundice can lead to brain damage and mental retardation.

Most people with G6PD deficiency can lead fairly normal lives, but they must be cautious to avoid certain medications and other triggers, including

• Aspirin (may be tolerated, depending on which type of G6PD abnormality is present)
• Antibiotics:  Chloramphenicol, Dapsone, Nitrofurantoin, Quinolones (e.g. ciprofloxacin), Sulphonamides (e.g. co-trimoxazole or Septrin)
• Antidiabetic medication: Glibenclamide
• Anti-gout medications:Probenecid
• Antimalarials:Quinine, Chloroquine, Pamaquine, Primaquine
• Chemotherapy:Doxorubicin (“Adriamycin”)
• Methylene blue
• Sulfasalazine, mesalazine
• Vitamin K
• Certain FOODS:Broad (“fava”) beans, Mangetout (“snow peas”)
• CHEMICAL SUBSTANCES: naphthalene, found in moth balls

These triggers can cause oxidative stress resulting in a haemolytic crisis. Infections, either bacterial or viral, can also cause oxidative stress and lead to bouts of haemolytic anaemia. With haemolytic anaemia, RBCs are destroyed at an accelerated rate and the patient becomes pale and fatigued (anaemic) as their capacity for providing oxygen to their body decreases. In some cases, jaundice can also be present during episodes of haemolysis. Most of these episodes are self-limiting, but if a large number of RBCs are destroyed and the body cannot replace them fast enough, then the affected patient may require a blood transfusion or even develop kidney problems. A small percentage of those affected with G6PD may experience chronic anaemia.