“One in two tuberculosis patients either has diabetes or pre-diabetes, that is every other TB patient has some sort of glucose metabolism disorder, shows our research,” says Dr. Vijay Viswanathan, senior Chennai-based diabetologist and President of Prof. M. Viswanathan Diabetes Research Centre. 

Dr. Viswanathan has done extensive research involving patients which are affected by both TB and diabetes as a part of the government-run Regional Prospective Observational Research for TB (RePORT) India consortium, which collaborates internationally to publish cutting-edge research on TB.

Dr Viswanathan’s latest study published in Diabetes and Metabolic Syndrome in May this year, directs the spotlight on TB patients who do not conventionally fall under the ‘diabetic,’ category, but have HBA1C levels between 5.7 and 6.4, or elevated fasting glucose levels between 100 and 125 mg/dl. 

Dr Vishwanathan and his team conducted two studies – Effect of Diabetes on TB Severity (EDOTS) and later Effect of Pre-Diabetes on TB Severity (EPOTS) in collaboration with National Institute of Research in TB (NIRT) Chennai and University of Massachusetts in the U.S. 

In the EPOTS study, 569 new TB cases were enrolled from government-run TB units in North Chennai, Tamil Nadu. Of these, 187 patients were included in the study with 76 TB patients who had normal blood sugar (normoglycemia) levels and 111 TB patients having HBA1C levels between 5.7% to 6.4% indicating pre-diabetes. 

At the end of the intensive phase of TB treatment, while only 8.6% with normoglycemia remained sputum smear positive, nearly 23.8% TB patients with pre diabetes remained sputum smear positive. “Treatment outcomes like relapse and death were relatively higher among people with TB pre-diabetes compared to TB patients who had normal blood sugar,” Dr Vishwanathan points out. Higher rate of deaths occurred in the TB pre-diabetes group (6.3%) compared to the TB normoglycemia group (1.3%). 

Diabetes, Undernutrition, tobacco, alcohol, and HIV are five main contributing factors to catching TB infection, Dr Vishwanathan says.

Screening and identification of pre-diabetes at the time of TB diagnosis, more careful monitoring during and after TB treatment may have a positive impact on TB treatment success, he says. Annual screening for diabetes among those people who had pre-diabetes at the time of TB diagnosis may help them intervene at an early stage to prevent or delay development of diabetes.

But currently pre-diabetic TB population falls through the cracks of National TB Elimination Programme (NTEP) and are not easily picked up for focussed care.

Almost all diabetes screening for TB is done in states through random blood sugar testing which is also known as the finger prick method.

“A random blood sugar test is effective for patients who have blood sugar over 200 mg/dl with symptoms like polyuria, polydipsia, weight loss. However, most pre-diabetes patients don’t have symptoms, that’s where the catch is, many people who later turn diabetic can remain asymptomatic for years,” Dr Vishwanathan explains. 

This is also because testing for random blood sugar is the cheapest. In the retail market, the cost for one such test is between Rs. 50-100. In public health settings, costs are set to further go down.

As an alternative, Dr Vishwanathan says that testing for fasting blood sugar should be included in diabetes screening programmes for TB patients. “Cost of processing a fasting blood sugar sample will be similar to that of conducting a Random Blood Sugar test, hence it can be viable,” a senior official from a leading private lab chain says.

“It is high time the government woke up and implemented a proper screening protocol. If a patient’s fasting blood sugar is more than 100 mg/dl, then this should be viewed seriously. 

Only in screened patients with above 100 mg/dl fasting blood sugar patients, should an Oral Glucose Tolerance (OGT) test be done,” he says. OGT is a very cumbersome test, as it requires a patient to be present and waiting in the clinic for nearly two hours after the fasting blood sugar sample is drawn. After two hours, the patient is fed a dose of oral glucose and the sample is redrawn to compare levels. OGT tests are slightly more expensive ranging between Rs 200 to Rs 300, while HBA1C tests for diabetes range between Rs 400 to Rs 600 per test. 

According to the Atlanta-based Centres for Disease Control and Prevention (CDC), a fasting blood sugar of 100 to 125 mg/dl indicates pre-diabetes and 126 mg/dl or higher indicates you have diabetes. 

“If you want to end TB by 2025, try and give more emphasis on diabetes and pre-diabetes patients as well as try and reduce its prevalence. Because if you don’t do that, there are still 50-100 million people with glucose metabolic disorders, and the end TB goal will not be achieved,” he told The Hindu.

Another popular blood test to test diabetes is checking HBA1C levels. Dr Vishwanathan’s team found in their research that a cutoff point of 6.5% or more had low sensitivity and would fail to diagnose diabetes in 60% of patients. 

“In Asian Indians HBA1C cut off of 6.1% – 6.3% was optimal. A much higher percentage of subjects would have been diagnosed with diabetes using HBA1C if we had used lower cut off points specific for Asian Indians,” says Dr Arutselvi Devarajan, Epidemiologist, RePORT India consortium. “We also found a lower cut off for diagnosis of diabetes among TB patients,” she adds. 

“Also, HBA1C is not very effective in picking up pre-diabetes. And it is an expensive test, hence it is not recommended for public health screenings,” says Dr Vishwanathan.