Diabetes and glycemic control, it turns out, plays a major role in the success of pulmonary tuberculosis (TB) outcome in patients, according to a study published online March 30 in the Public Library of Science.

Led by Chen Yuan Chiang with the International Union Against Tuberculosis and Lung Disease and Taipei Medical University in Taiwan, the research sought to assess the influence of diabetes mellitus (DM) glycemic control and diabetes-related complications on the outcome of TB treatments.

“As clinical manifestations of pulmonary TB are likely related to immune status and hyperglycemia is associated with changes of immune response, we hypothesized that the influence of DM on clinical manifestations of pulmonary TB is related to glycemic control,” Chen and team wrote.  “As complications of chronic hyperglycemia may have an impact on outcome of TB treatment, we further hypothesized that this effect is mediated through diabetes-related comorbidities.”

The study examined culture positive pulmonary TB patients at three hospitals in Taiwan between 2005 and 2010. The patients were assessed by glycated haemoglobin (A1C) categorized into three groups:
• HbA1C less than 7 percent (pretreatment levels)
• HbA1C between 7 and 9 percent
• HbA1C greater than 9 percent

A total of 1,473 patients were enrolled—705 with DM and 768 without DM. Of the diabetic patients, more than 11 percent had pretreatment levels of HbA1C, 21.6 percent had levels between 7 and 9 percent and 39 percent of diabetic patients had HbA1C levels greater than 9 percent.

All participants were given a TB smear test and 58 percent were positive.
“The proportion of patients with a high smear positivity grade (3+ or 4+) was significantly higher among diabetic patients than non-diabetic patients,” the researchers wrote, noting the difference was 43 and 33 percent, respectively.

In studying the patients in one year from initial smear testing, results showed that the influence of DM on outcome of TB treatment was not proportionally related to the pretreatment of HbA1C, but mediated through diabetes-related issues.

“Patients with diabetes-related comorbidities had an increased risk of unfavorable outcome and one year mortality. However, diabetes was not associated with amplification of resistance to H or to R,” the authors wrote.

The study showed that patients with poor glycemic control had more TB symptoms and were more likely to test positive for TB with a higher positivity grade.

“This suggests that proper glycemic control may reduce the frequency of symptoms and smear positivity grades, hence the risk of transmission of tuberculous infection,” Chen and colleagues concluded.