Blood sugar disorders have become one of the defining global health challenges of the 21st century. Diabetes, particularly type 2 diabetes, is rising at an alarming pace worldwide, driven by ageing populations, sedentary lifestyles, dietary changes, and urbanisation.
One of the most widely used tools for diagnosing and monitoring diabetes is the glycated haemoglobin test, commonly known as HbA1c. This test measures the percentage of haemoglobin in the blood that has glucose attached to it, reflecting average blood sugar levels over the past two to three months. Clinically, an HbA1c level below 5.7 per cent is considered normal, levels between 5.7 per cent and 6.4 per cent indicate prediabetes, and levels of 6.5 per cent or higher are used to diagnose diabetes. Because the test does not require fasting and provides a long-term picture of glucose control, it has become a cornerstone of diabetes diagnosis and monitoring worldwide.
However, a new evidence-based viewpoint published in The Lancet Regional Health- Southeast Asia warns that this standard test may not accurately reflect blood glucose levels in South Asian populations, including Indians. The study, led by Professor Anoop Misra and collaborators, raises concerns that HbA1c readings can be distorted by underlying blood disorders that are common in India, potentially leading to misdiagnosis, delayed treatment, or inappropriate management.
The concern is particularly significant for India, which carries one of the world’s largest diabetes burdens. It is estimated that about 7.7 crore people above the age of 18 in India are living with type 2 diabetes, and nearly 2.5 crore more are prediabetic, placing them at high risk of developing the disease in the near future.
Alarmingly, more than 50 per cent of individuals remain unaware of their diabetic status, increasing the likelihood of complications. Adults with diabetes face a two- to three-fold higher risk of heart attacks and strokes. Reduced blood flow and nerve damage can lead to foot ulcers, infections, and even limb amputations. Diabetes is also a major cause of blindness through diabetic retinopathy and is among the leading causes of kidney failure. In this context, the study may provide critical insights into improving diagnosis and preventing long-term complications through more accurate testing strategies.
Why the standard diabetes test may misdiagnose?
The Lancet viewpoint highlights that while HbA1c is widely used and convenient, its reliability depends on the assumption that haemoglobin behaves similarly in all individuals. This assumption may not hold true in populations where blood disorders such as anaemia, haemoglobinopathies, or enzyme deficiencies are common.
“In the Indian subcontinent, the rising number of people with type 2 diabetes (T2D) makes it essential to maintain good glycemic control to prevent a substantial burden of diabetes-related complications,” the authors noted. Accurate diagnosis is crucial not only for identifying diabetes but also for detecting prediabetes early, when interventions can prevent progression.
Clinicians favour HbA1c because of its practical advantages. The test does not require fasting, reflects long-term glucose trends, and is recommended by major organisations, including the World Health Organisation and the American Diabetes Association. However, researchers emphasise that its roles in diagnosis and monitoring are distinct and can be affected by patient-specific biological factors.
The study explains that HbA1c results depend on the structure, quantity, and lifespan of red blood cells. Any condition that alters these factors can distort readings. “Its widespread use—and the tendency toward oversimplification by both physicians and patients—can lead to misinterpretation, particularly in populations with altered erythrocyte dynamics, such as those with anaemia or hemoglobinopathies,” the authors wrote.
In India, these conditions are highly prevalent. Anaemia, especially iron deficiency anaemia, affects a large proportion of the population due to nutritional deficiencies and other health factors. Similarly, inherited haemoglobin disorders and enzyme deficiencies such as glucose-6-phosphate dehydrogenase (G6PD) deficiency are more common in South Asia than in many other regions.
HbA1c works by measuring how much glucose has attached to haemoglobin over time. But if red blood cells live longer or shorter than normal, or if haemoglobin structure is altered, HbA1c levels may not accurately reflect true blood sugar levels. This means some individuals may appear to have normal glucose levels when they actually have diabetes, while others may appear diabetic when their glucose levels are normal.
“Relying exclusively on HbA1c can result in misclassification of diabetes status,” said Professor Anoop Misra, corresponding author and Chairman of Fortis C-DOC Centre of Excellence for Diabetes. “Some individuals may be diagnosed later than appropriate, while others could be misdiagnosed, which may affect timely diagnosis and management.”
The study also highlights the impact of G6PD deficiency, an inherited enzyme disorder affecting red blood cells. In such cases, HbA1c may underestimate blood glucose levels, potentially delaying diagnosis by up to four years in some individuals. This delay increases the risk of complications such as heart disease, nerve damage, kidney failure, and vision loss.
Laboratory factors can also influence accuracy. Differences in testing equipment, quality control standards, and laboratory practices can produce inconsistent results, especially in low-resource settings. This makes it even more challenging to rely solely on HbA1c for diagnosis and monitoring.
Because of these limitations, the researchers emphasise that HbA1c should not be treated as a universal or standalone diagnostic tool, particularly in populations with a high prevalence of blood disorders.
Rethinking diabetes diagnosis and monitoring in India
The study outlines important clinical and policy recommendations to improve diabetes diagnosis and monitoring in South Asian populations. The authors stress that healthcare providers should adopt a more comprehensive and context-specific approach rather than relying solely on HbA1c.
“For diagnosis of prediabetes or type 2 diabetes, standardised oral glucose tolerance test (OGTT) should remain the gold standard for diagnosis,” the authors stated. The OGTT involves measuring blood glucose levels before and two hours after consuming a glucose solution, providing a direct assessment of the body’s glucose metabolism.
HbA1c can still play a role, but it should be used to support, rather than replace, glucose-based testing. “HbA1c may be used to corroborate this diagnosis but should not serve as the sole diagnostic tool, particularly in populations with prevalent haematological abnormalities,” the study noted.
For ongoing monitoring, combining HbA1c with fasting and post-meal blood glucose measurements provides a more accurate assessment of long-term glycemic control. Where available, continuous glucose monitoring systems (CGM) can offer additional insights by tracking glucose fluctuations throughout the day.
The study also recommends routine evaluation of blood health in cases where HbA1c results do not match clinical findings. “Hematologic parameters should be routinely assessed, particularly the RDW. When RDW is elevated or discordance persists, a targeted work-up–including complete blood count, peripheral blood smear, iron studies, and haemoglobin electrophoresis should be considered.”
In resource-limited settings, practical alternatives such as self-monitoring of blood glucose using portable glucose meters, combined with basic blood tests, can provide reliable guidance. These approaches are particularly important in rural and tribal areas, where anaemia and haemoglobin disorders are more prevalent.
Beyond clinical practice, the study highlights major implications for public health policy in India. National diabetes surveillance programs often rely heavily on HbA1c-based estimates. However, this approach may produce inaccurate prevalence figures in populations with widespread anaemia and haemoglobin abnormalities.
“Prevalence data from India should not rely solely on HbA1c, as doing so may lead to overestimation of prediabetes and diabetes,” the authors warned. Such inaccuracies can distort public health planning and lead to inefficient allocation of healthcare resources.
The researchers emphasise the need for standardised laboratory practices, improved diagnostic protocols, and the development of diagnostic tools tailored specifically to Indian populations. Physicians should interpret HbA1c results alongside clinical history, blood tests, and other glucose measurements, rather than relying on a single number.
This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS.
