Favism (G6PD deficiency): what should you avoid?

Red blood cells need an enzyme called G6PD to protect themselves against "oxidative" damage (a kind of chemical damage) ^[2]. In G6PD deficiency this enzyme is low, so when the body meets certain foods, medicines, chemicals or infections, red blood cells can suddenly be destroyed. This destruction is called "haemolysis", and the anaemia it causes is called "haemolytic anaemia" ^[2].

The word "favism" originally means a haemolytic attack after eating fava beans ^[2], but it is often used for G6PD deficiency itself. The condition is inherited; it is neither cancer nor contagious ^[1]. Around 500 million people worldwide have G6PD deficiency, and most of them never have symptoms in their lifetime ^[1].

Why is it more common in men? The G6PD gene is on the X chromosome ^[2]. Men have only one X chromosome, so if that single copy is faulty, they have the deficiency. Women have two X chromosomes and most are "carriers"; but the amount of enzyme in carrier women varies from normal to very low, and some of them can also have haemolysis just like men ^[2].

How common is it? It is common in many countries; in Iran, an analysis that combined 36 studies of nearly 150,000 people found that about 1 in 15 people had G6PD deficiency: about 1 in 11 men and about 1 in 45 women ^[3]. How common it was varied widely between regions of that country, from fewer than 1 to about 15 in every 100 people ^[3].

Get to know other common types of anaemia too: thalassaemia minor, iron-deficiency anaemia and vitamin B12 deficiency.

The key to living well with G6PD deficiency is avoiding triggers; this is the most effective way to prevent haemolysis ^[14]. These are the most important ones:

What about other foods? Some lists ban other foods as well. But a review of the studies found conclusive evidence for no food other than fava beans, and food additives, at the levels permitted in North America, were safe for most people with the deficiency ^[5]. An expert guideline also found no reliable evidence of risk from other foods ^[2].

What about other medicines? Many common medicines, at usual doses, carry no added risk for people with G6PD deficiency ^[2]. But do not decide the list yourself: before taking any medicine, even one bought without a prescription, tell your doctor and pharmacist that you have G6PD deficiency ^[2].

During breastfeeding: a few cases have been reported in which a breastfed baby with G6PD deficiency developed haemolysis after the mother ate fava beans ^[7]. If your baby has G6PD deficiency, talk to your baby's doctor about eating fava beans while breastfeeding. The medicine tafenoquine must not be used while breastfeeding a baby who has G6PD deficiency or whose status is unknown ^[9].

A haemolytic attack usually starts after a trigger, such as eating fava beans, a particular medicine or an infection ^[1]. Know these signs ^{[8, 9]}:

• Dark urine (dark red or brown)
• Yellowing of the whites of the eyes or of the skin
• Pale skin, tiredness and feeling unwell
• Dizziness, light-headedness, confusion or shortness of breath
• Darkening of the lips

Most attacks are treated well if they are recognised early ^[1]. In hospital, the doctor checks how severe the anaemia is with blood tests, gives fluids through a drip and, if the anaemia is severe, a blood transfusion ^[8]. In a study of 308 children with favism attacks in Iran, most attacks were caused by eating fava beans, most children were treated with fluids, and about 1 in 3 needed a blood transfusion ^[8].

The enzyme deficiency itself is inherited and lifelong; there is still no medicine that treats it ^[15]. That is why the most important thing after any attack is to identify the trigger and avoid it, so that the attack does not happen again ^[14].

G6PD deficiency increases a newborn baby's risk of severe jaundice. This jaundice can rise quickly and, if not treated in time, can cause permanent brain damage (kernicterus) ^[7]. Newborn jaundice is treated with light therapy (phototherapy), and an exchange transfusion is sometimes needed ^{[7, 13]}.

In a review from Iran of babies admitted to hospital with jaundice, about 1 in 14 had G6PD deficiency, about 4 times as often in boys as in girls ^[12].

Newborn screening. The World Health Organization recommends testing all newborn babies in countries where this deficiency is common ^[7]. Some of these countries, such as Iran, have introduced newborn screening programmes for G6PD deficiency ^{[4, 11]}. In one Iranian province, hospital admissions for haemolytic attacks fell by almost half after newborn screening started ^[4].

But the simple screening test does not find everyone with the deficiency, especially girls ^{[7, 11]}. So if your baby's screening result was normal but signs of haemolysis appear later, or there is G6PD deficiency in your family, tell your doctor so that a more accurate test that measures the amount of enzyme can be done ^{[2, 11]}.

If your baby has G6PD deficiency, take their jaundice seriously and do not store their clothes with naphthalene ^[7].

G6PD deficiency is diagnosed with a blood test that measures the activity of the G6PD enzyme in red blood cells ^[2]. Simple (qualitative) tests only show whether the enzyme is very low or not; "quantitative" tests measure the amount of enzyme and are more accurate for women and for people with moderate deficiency ^{[7, 11]}.

Timing matters. During a haemolytic attack or shortly after it, and after a blood transfusion, the result can wrongly come back as normal, because younger red cells and donated blood contain more enzyme ^[2]. If you were tested at such a time, do not take a normal result as final; talk to your doctor about repeating it ^[2].

In women, the amount of enzyme can be normal, slightly low or very low; this is why women need a quantitative test, and a genetic test alone is not enough ^[2]. To read a blood count report: understanding your CBC results.