Rethinking the ‘gold standard’: Why HbA1c test may be failing India’s 101 million diabetics

“Recently, another study was published in The Lancet that estimated the prevalence of diabetes in India using HbA1c, which would not reflect the true picture. So, we decided to write about the challenges of using the test,” said Dr Anoop Misra, chairman of Fortis C-DOC Centre for diabetes and one of the authors of the paper.

First, what is HbA1c test?

HbA1c or glycated haemoglobin is a way to measure blood sugar levels over the previous two or three months. This is done by checking the percentage of haemoglobin — the oxygen-carrying protein — that is coated with glucose. An HbA1c level of less than 5.7 per cent is considered normal; anything between 5.7 per cent and 6.4 per cent is considered prediabetes; levels over 6.5 per cent are considered diabetes.

Since the link between blood sugar control and HbA1c levels was established in 1976, this test has become the gold standard for assessing glycemic control. This was also proposed as a diagnostic method in 2010 owing to its convenience. The test does not require people to fast, unlike the traditional blood sugar test; it is more stable pre-analysis, and the variability within a person is low.

Why do researchers say it’s not accurate?

The researchers have reviewed various studies comparing blood sugar levels measured using different methods and found that there appears to be variation. For example, a recent study of 1,120 people from south India showed that an oral glucose tolerance test identified more prediabetes cases (87.8 per cent) than HbA1c (45.4 per cent), with minimal overlap. Whereas, in another study of 116 young adults from Pune, HbA1c identified a higher prevalence of prediabetes (23.3 per cent) compared to the OGTT (7.8 per cent).

The reason for these differences, the researchers say, is the variation in the red blood cell levels, lifespan, and how they get coated in glucose. Dr Misra said, “HbA1c levels are influenced by multiple factors, the most important being haemoglobin levels. This means any condition that affects the haemoglobin levels, such as iron deficiency anaemia or the G6PD deficiency that causes the blood cells to break down, will change the HbA1c levels.”

Dr Shashank Joshi, diabetologist at Lilavati Hospital and one of the authors of the study, said, “This is significant in India considering the high burden of anaemia across the country, presence of haemoglobinopathies such as thalassaemia and sickle cell disease in certain populations, and prevalence of conditions such as malaria that also affect the haemoglobin levels. In this scenario, the HbA1c levels may not present an accurate picture,” said.

He added, “The problem is not with the test itself. It is commonly used in the West where there is not so much variation in the population. But in India, where such conditions are common, one has to be mindful.

So, what can you do?

The study also suggests using measures such as self-monitoring of glucose levels or continuous glucose monitoring. “Oral glucose tolerance test can be used for diagnosis and people can test their blood sugar levels frequently to keep a check on their blood sugar control. If a person measures their blood glucose levels two or three times in a week, over a period of time, we will be able to tell what is happening without the need for an HbA1c test,” said Dr Misra.