A condition that makes blood sugar appear falsely low can cause years‑long delays in type 2 diabetes diagnoses, UK Biobank data have revealed.
Summary
Genetic information from UK Biobank participants has revealed how a silent condition that affects one in seven Black men can delay a type 2 diabetes diagnosis by several years. Those with the condition, called G6PD deficiency, are also more likely to experience diabetes complications such as blindness and kidney failure. The researchers behind the study are now working to make genetic tests for G6PD deficiency available to Black communities.
One in seven Black men in the UK has a genetic condition called G6PD deficiency that can delay a type 2 diabetes diagnosis by years and makes them more likely to experience diabetes complications such as blindness and kidney failure. The researchers behind the study are now pushing for routine NHS testing for G6PD deficiency in some communities.
Standard test misses the mark
The standard test doctors use to diagnose diabetes shows the average blood sugar level over the last few months by measuring how much sugar has attached to red blood cells. The test assumes that everyone’s red blood cells have the same lifespan, after which they die off and are naturally replaced. But the red blood cells of people with G6PD deficiency die off and are replaced more quickly.
“Even if the sugar levels in the blood are the same, the cells don’t live long enough to get as much sugar attached to them,” explains study leader Inês Barroso from the University of Exeter, UK. “If the turnover [of red blood cells] is a lot quicker, then most cells would be young – and those don’t have as much sugar attached to them yet. So, the test under-reads the glucose.”
G6PD deficiency is an evolutionary adaptation that protects against severe malaria because it stops the parasite from growing in red blood cells. It’s most common in people whose ancestors came from areas where malaria used to be common: Africa, Asia and the Mediterranean region.
How genetics skew diabetes care
By the time they get a [diabetes] diagnosis, they might have already progressed to complications.
Professor Inês Barroso, University of Exeter, UK
Genetic information from UK Biobank participants has now revealed that G6PD deficiency affects one in seven Black men and one in 63 men from South Asian backgrounds – but fewer than one in 10,000 white men. Only around one in 50 people know that they have the condition because it rarely causes any problems.
On average, G6PD-deficient men who develop diabetes get their diagnosis more than four years later. They also have nearly 1.4 times higher odds of complications such as diabetic retinopathy, which causes vision loss and blindness. “By the time they get a [diabetes] diagnosis, they might have already progressed to complications,” Barroso says.
G6PD deficiency doesn’t affect women the same way because the G6PD gene is located on the X chromosome. Women tend to have two X chromosomes, so they often have one affected as well as one ‘regular’ copy of the G6PD gene and never develop the deficiency. Men, with typically only one X chromosome, develop the condition as soon as they have one copy of the affected gene.
Screening could tackle inequality
These findings are not surprising at all – they bolster evidence from previous studies and reinforce the long-held belief regarding how G6PD deficiency may contribute to diabetes inequalities.
Dr Ayush Giri, Vanderbilt University, US
“These findings are not surprising at all – they bolster evidence from previous studies and reinforce the long-held belief regarding how G6PD deficiency may contribute to diabetes inequalities,” comments Ayush Giri from Vanderbilt University in the US, who has also done research on G6PD deficiency and diabetes.
The study clearly shows that out of two people with a similarly high diabetes risk who receive the standard diabetes test, “the individual without the deficiency goes on to be flagged as pre-diabetic and the individual with the deficiency does not”, Giri explains. He calls this “a powerful demonstration” of how clinical care differs due to reliance on one test.
Barroso and her team are now working with NHS England and others to explore routine testing for G6PD deficiency in some communities. “I think there are things we should be doing now to avoid perpetuating inequality in diagnosis and treatment,” she says. “The World Health Organisation suggests that if G6PD deficiency is prevalent in more than 5% of the population, you should screen for it – in the Black communities in the UK, [the prevalence] is 15%.”
Related publication
- Diabetes Care, August 2025
