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• Diabetes control status and TB treatment response: confounded by treatment adherence?
  Richard D Turner
  Published on: 18 September 2017

• Published on: 18 September 2017

  Diabetes control status and TB treatment response: confounded by treatment adherence?

  • Richard D Turner, Consultant Respiratory Physician King's College Hospital, London

  The paper by Yoon et al [1] addressees an important subject - diabetes mellitus (DM) probably increases the risk of TB by a factor of three [2]. The authors present data showing an association of poorer diabetes control status with both the characteristics of pulmonary TB at presentation, and the response to treatment. Compared to patients with no or controlled DM, those with uncontrolled DM reported worse symptoms at presentation, were more likely to be sputum smear positive, and had more substantial radiographic changes. Patients with uncontrolled DM were also more likely to remain sputum culture positive at two months, and either fail treatment or die.

  Although these observations are entirely consistent with a biologically plausible explanation that hyperglycaemia itself influences the development of TB and its response to treatment, there is an important confounding factor which may not have been fully accounted for: treatment adherence, and the wider general use of health care.

  Patients with uncontrolled diabetes, by definition, are less well treated than those with controlled diabetes. Part of the reason for this will be treatment adherence. Such patients may also be less well engaged with health services. Hence a reason for more advanced TB disease at diagnosis in those with uncontrolled DM compared to controlled or no DM might be due to later presentation to health services. Indeed, a recent study in China reported that patients with hyperglycaemia a...

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  The paper by Yoon et al [1] addressees an important subject - diabetes mellitus (DM) probably increases the risk of TB by a factor of three [2]. The authors present data showing an association of poorer diabetes control status with both the characteristics of pulmonary TB at presentation, and the response to treatment. Compared to patients with no or controlled DM, those with uncontrolled DM reported worse symptoms at presentation, were more likely to be sputum smear positive, and had more substantial radiographic changes. Patients with uncontrolled DM were also more likely to remain sputum culture positive at two months, and either fail treatment or die.

  Although these observations are entirely consistent with a biologically plausible explanation that hyperglycaemia itself influences the development of TB and its response to treatment, there is an important confounding factor which may not have been fully accounted for: treatment adherence, and the wider general use of health care.

  Patients with uncontrolled diabetes, by definition, are less well treated than those with controlled diabetes. Part of the reason for this will be treatment adherence. Such patients may also be less well engaged with health services. Hence a reason for more advanced TB disease at diagnosis in those with uncontrolled DM compared to controlled or no DM might be due to later presentation to health services. Indeed, a recent study in China reported that patients with hyperglycaemia are more likely to delay presenting to health services with symptoms of pulmonary TB [3].

  And at least part of the reason for delayed sputum culture conversion in uncontrolled DM in the current study could be poorer adherence to TB treatment. Although this was not entirely borne out by the data, there was a suggestion of poorer treatment compliance in patients who remained culture positive at two months compared to those who did not (Table 3; p=0.22). It is not clear from the paper how TB treatment compliance was associated with DM control status. Neither is it clear precisely what methods were employed by the TB nurse in the study to assess treatment adherence.

  So although the findings of Yoon et al support a direct effect of diabetes control status on TB presentation and treatment response, further work is required to exclude the potential confounding effects of delayed presentation of TB and adherence to treatment. Health records could be used to assess level of engagement with health services prior to the TB diagnosis, and directly-observed TB treatment in all study subjects could address potential compliance issues.

  References:

  1. Yoon YS, Jung JW, Jeon EJ et al. The effect of diabetes control status on treatment response in pulmonary tuberculosis: A prospective study. Thorax. 2017; 72: 263–70.

  2. Jeon CY, Murray MB. Diabetes mellitus increases the risk of active tuberculosis: A systematic review of 13 observational studies. PLoS Med. 2008; 5: e152.

  3. Wang Q, Ma A, Han X et al. Hyperglycemia is associated with increased risk of patient delay in pulmonary tuberculosis in rural areas. J Diabetes. 2017; 9: 648–655.

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  Conflict of Interest:
  None declared.

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