Common Diabetes Test Could Be Inaccurate For Millions: Lancet Study

Leading Indian endocrinologists have cautioned that a standard blood test—HbA1c—widely used to diagnose and monitor diabetes may be yielding misleading results for large sections of the population, potentially distorting both individual treatment decisions and national estimates of the disease burden.

The warning comes in an analysis published in the latest journal of Lancet Regional Health – Southeast Asia, which examines the limitations of HbA1c, the test that measures the proportion of glucose bound to haemoglobin in red blood cells and is considered the global benchmark for long-term blood sugar control.

According to the authors, the reliability of HbA1c can be significantly affected in populations with high rates of anaemia, inherited haemoglobin disorders, and glucose-6-phosphate dehydrogenase (G6PD) deficiency—conditions that are common in India. G6PD deficiency, a genetic disorder, causes red blood cells to break down faster than usual, which can lead to deceptively low HbA1c values and delay a diagnosis of diabetes.

India has an estimated 10.1 crore people living with diabetes and another 13.6 crore with prediabetes, as per the ICMR–INDIAB study. Even small systematic inaccuracies in diagnosis, the authors said, can therefore have consequences at a population scale.

“HbA1c is popular because it is simple and convenient. But when relied on alone it can misclassify patients,” said Dr. Anoop Misra, chairman of the Fortis C-DOC Centre of Excellence for Diabetes and the corresponding author of the paper. “Some individuals may be diagnosed late and miss early intervention, while others might be started on treatment they do not yet require.”

The test works on the assumption that red blood cells survive for about three months. However, illnesses that alter haemoglobin levels or shorten the lifespan of these cells—such as iron-deficiency anaemia or thalassaemia traits—can skew the results. The National Family Health Survey (NFHS-5) found that over 57% of women and nearly a quarter of men in India are anaemic, raising the possibility that HbA1c readings may not accurately reflect true glucose levels for a substantial proportion of people.

The authors noted that in men with undetected G6PD deficiency, depending solely on HbA1c could postpone the diagnosis of diabetes by several years. Such delays increase the likelihood of complications involving the kidneys, eyes, nerves, and heart, ultimately raising healthcare costs.

Dr. Shashank Joshi, a Mumbai-based endocrinologist and co-author, said that biological variation is only part of the problem. “Even in advanced urban centres, HbA1c values can be influenced by blood disorders. In rural and tribal populations, where anaemia is more prevalent, the divergence between measured and actual glycaemia could be even greater,” he said.

Beyond clinical care, the study flags implications for public health planning. Screening programmes and epidemiological surveys that depend exclusively on HbA1c might either overestimate or underestimate prevalence, influencing how governments allocate resources, procure medicines, and design prevention strategies.

To address the issue, the researchers advocate a more context-sensitive diagnostic approach. In low-resource settings, oral glucose tolerance tests combined with periodic self-monitoring and basic fasting and post-meal glucose measurements may provide a more reliable picture. In tertiary-care centres, HbA1c should be interpreted alongside additional tools such as continuous glucose monitoring and alternative biochemical markers like fructosamine.

“Using a combination of tests gives clinicians a truer assessment of control and risk,” said Dr. Shambho Samrat Samajdar, a co-author and well-known diabetologist from Kolkata. “That is essential not only for treating patients but also for planning health services.”

While the authors, including Dr. Naval K. Vikram, Professor of Medicine at the All India Institute of Medical Sciences (AIIMS), Delhi, emphasised that the test will continue to play an important role, they maintained that excessive dependence on a single biomarker in a country with widespread blood disorders could carry hidden medical and economic costs.