The test doctors trust most, quietly misleading some patients
If you have ever had a blood test called HbA1c, you already know a bit of this story.
HbA1c is the go-to test for diabetes. It measures the average level of sugar stuck to your red blood cells over the past three months. Doctors rely on it worldwide. Insurance companies rely on it. Prevention programs rely on it.
But a new study shows that for some people, this trusted test is quietly lying.
Diabetes is growing fastest in populations of South Asian ancestry. People with roots in India, Pakistan, Bangladesh, Sri Lanka, and neighboring regions face higher rates at earlier ages than most other groups.
At the same time, these patients often get diagnosed late. Doctors have long suspected something was off. This study points to a possible reason hiding inside our genes.
Old view vs. new view
Until recently, the common view was that a normal HbA1c meant normal blood sugar. Simple. Clean.
But HbA1c depends on more than blood sugar. It also depends on the life span and biology of red blood cells. If red cells turn over faster, less sugar has time to stick to them. The test can come back low even when actual glucose in the blood is high.
That is exactly what this new research found is happening in a common South Asian gene variant.
How it works, in plain English
Picture red blood cells as little boats that carry sugar stickers. Every day they drift around, collecting more stickers. The HbA1c test counts the stickers.
Now imagine someone's boats get replaced faster than average. New boats arrive with no stickers. The sticker count stays low, even if the harbor is full of sugar.
A gene called PIEZO1 helps shape how red blood cells form and how long they live. A specific variant of PIEZO1 nudges those cells to turn over a bit faster. The stickers never pile up the same way.
For blood sugar, those patients look just as healthy as anyone. For HbA1c, they look even healthier. But their actual glucose may be rising in the background.
The study snapshot
Researchers analyzed data from two very large groups of South Asians. One was nearly 20,000 South Indians. The other was over 43,000 British Bangladeshis and British Pakistanis.
They checked whether the PIEZO1 variant affected HbA1c, fasting glucose, post-meal glucose, and insulin markers. Then they looked at who got diagnosed with prediabetes, diabetes, and diabetic eye disease over time.
Here's what they found
Carriers of the variant had lower HbA1c, just as expected. But their actual blood sugar looked the same as non-carriers. That confirms the mismatch is in the red cells, not in true glucose control.
Because of that mismatch, carriers were less likely to meet the cutoff for a diabetes diagnosis. They were 37 percent less likely to be diagnosed with prediabetes and 15 percent less likely to be diagnosed with type 2 diabetes.
Fewer diagnoses might sound like good news. It is not.
But here is the catch.
Carriers with diabetes were 20 percent more likely to develop diabetic eye disease, a serious complication that can cause vision loss.
That pattern points in one direction. Their diabetes was being missed, then discovered only after it had caused damage.
In a simulated population of 100,000 South Asians aged 40 to 50, the researchers estimated about 1,019 missed prediabetes diagnoses and 303 missed diabetes diagnoses over 10 years.
How the researchers read it
The authors argue that HbA1c alone may not be enough for safe diabetes screening in South Asian patients. They suggest either lowering the cutoff for this group or adding backup tests like fasting glucose.
They also flag a public health cost. Prediabetes diagnoses open the door to prevention programs. Missed diagnoses close that door before it can help.
If you are of South Asian ancestry, ask your doctor about more than just HbA1c. A fasting glucose test or an oral glucose tolerance test can catch problems the standard test may miss.
Family history, weight, blood pressure, and cholesterol also matter. Use the full picture. Do not lean on a single number.
If you are not South Asian, this study is still a reminder. Lab tests are built on averages. Your body may fall outside the average in ways that matter.
The limits
The study is observational, so it shows patterns, not proof. The researchers cannot fully rule out that other factors besides the gene variant influence the results.
It also focused on one variant of one gene. Other genes may have similar effects in other populations. More research is needed to find them.
Expect conversations about updating diabetes screening guidelines to account for ancestry-based genetic variation. Some countries may start offering cheap genetic screening alongside HbA1c, especially in high-risk populations.
Personalized medicine is moving from buzzword to bedside. This kind of research is what drives that shift.
