What Is G6PD Deficiency? A Simple Explanation
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited enzyme disorder in which the body produces insufficient levels of the G6PD enzyme. This enzyme plays a critical role in protecting red blood cells from oxidative damage. When G6PD levels are low, red blood cells may break down prematurely — a process known as haemolysis — particularly after exposure to certain foods, infections, or medications. A G6PD deficiency blood test measures the activity of this enzyme and can help identify whether someone carries this condition.
Favism is a term historically associated with G6PD deficiency, referring specifically to haemolytic episodes triggered by consuming fava beans (broad beans). While not everyone with G6PD deficiency will react to fava beans, the association is well documented in medical literature. Understanding your G6PD status through a straightforward G6PD blood test can be a valuable step in managing your long-term wellbeing.
Practical Insight: G6PD deficiency is one of the most common enzyme disorders worldwide, affecting an estimated 400 million people globally. In the UK, it is more frequently observed in individuals of African, Mediterranean, Middle Eastern, and South Asian heritage.
How Does G6PD Deficiency Affect Red Blood Cells?
The G6PD enzyme is essential for the pentose phosphate pathway — a metabolic process that generates NADPH, a molecule responsible for maintaining the antioxidant defences of red blood cells. Without adequate G6PD activity, red blood cells become vulnerable to oxidative stress.
When oxidative stress occurs — whether from certain medications, infections, or dietary triggers like fava beans — the affected red blood cells may rupture. This can sometimes lead to symptoms such as:
- Fatigue or unusual tiredness
- Pale or yellowish skin (jaundice)
- Dark-coloured urine
- Rapid heart rate
- Shortness of breath during episodes
These symptoms may indicate a haemolytic episode, and anyone experiencing them should seek appropriate medical advice promptly.
Practical Insight: Many individuals with G6PD deficiency remain entirely asymptomatic throughout their lives and may only discover the condition through routine blood screening or when a trigger causes an episode.
Who Should Consider a G6PD Deficiency Blood Test?
A G6PD deficiency blood test may be worth considering for a range of individuals. You may wish to consider testing if:
- You have a family history of G6PD deficiency or favism
- Your ethnic background includes African, Mediterranean, Middle Eastern, or South Asian heritage
- You have experienced unexplained episodes of jaundice, anaemia, or dark urine
- You are planning a family and wish to understand carrier status
- You are starting a new medication and want to check for potential interactions
- You are a parent and wish to screen a newborn or child with relevant family history
- You live in London and want convenient access to private blood testing without a lengthy wait — explore our blood test packages comparison guide to find the right option
At Walk In Clinic London, we provide nurse-led blood testing services for enzyme disorders including G6PD deficiency.
G6PD Deficiency Blood Test: What Does It Involve?
The G6PD deficiency blood test is a simple venous blood draw that measures the quantitative activity of the G6PD enzyme within your red blood cells. The process is quick, typically taking only a few minutes, and does not require fasting.
What Happens During the Test
- A trained nurse collects a small blood sample from your arm
- The sample is sent to an accredited laboratory for analysis
- Results are reported back to you, typically within a few working days
Practical Insight: It is generally recommended to avoid testing during or immediately after an acute haemolytic episode, as newly produced red blood cells (reticulocytes) may have higher G6PD levels, potentially leading to a falsely normal result.
Understanding Your G6PD Test Results
| Result Category | G6PD Enzyme Activity | What It May Suggest |
|---|---|---|
| Normal | Within standard reference range | G6PD enzyme activity appears adequate |
| Intermediate/Partial Deficiency | Below normal but not severely reduced | May indicate carrier status; some susceptibility to oxidative triggers |
| Deficient | Significantly below normal range | May suggest G6PD deficiency; red blood cells more vulnerable to oxidative stress |
Practical Insight: G6PD deficiency is an X-linked genetic condition, meaning it primarily affects males. Females can be carriers and may sometimes show intermediate enzyme levels.
G6PD Deficiency vs. Other Causes of Haemolytic Anaemia
| Feature | G6PD Deficiency | Sickle Cell Trait/Disease | Iron Deficiency Anaemia |
|---|---|---|---|
| Cause | Enzyme deficiency (genetic) | Haemoglobin abnormality (genetic) | Nutritional/blood loss |
| Inheritance | X-linked recessive | Autosomal recessive | Not inherited |
| Common Triggers | Fava beans, certain medications, infections | Dehydration, low oxygen, extreme temperatures | Low dietary iron, chronic blood loss |
| Screening Method | G6PD enzyme activity blood test | Haemoglobin electrophoresis | Serum ferritin, full blood count |
Frequently Asked Questions About G6PD Deficiency and Blood Testing
What is a G6PD deficiency blood test used for?
A G6PD deficiency blood test measures the activity level of the glucose-6-phosphate dehydrogenase enzyme in your red blood cells. It is used to identify whether someone has reduced enzyme activity, which may make their red blood cells more susceptible to damage from certain triggers.
Can favism be detected through a blood test?
Yes. Favism is closely associated with G6PD deficiency, and a G6PD enzyme activity blood test can help identify whether someone may be susceptible to haemolytic reactions triggered by fava beans.
Is G6PD deficiency common in the UK?
G6PD deficiency is relatively common globally and is seen in the UK, particularly among individuals of African, Mediterranean, Middle Eastern, and South Asian descent. You can read more in our detailed guide on G6PD deficiency symptoms, testing, and management.
Do I need to fast before a G6PD blood test?
No fasting is typically required before a G6PD deficiency blood test.
Can women have G6PD deficiency?
Yes, although G6PD deficiency is more common in males due to its X-linked inheritance pattern. Females can be carriers and may sometimes show intermediate or partially reduced enzyme levels.
Where can I get a G6PD deficiency blood test in London?
Walk In Clinic London offers nurse-led G6PD deficiency blood testing at our central London location. No GP referral is needed.
Medical Disclaimer
This blog post has been produced for educational and informational purposes only. The content does not constitute medical advice, diagnosis, or treatment. Walk In Clinic London provides nurse-led testing and reporting services only.
Written Date: 20 March 2026
Next Review Date: 20 March 2027
