Diabetes mellitus significantly increases the risk of developing active tuberculosis (TB) and worsens TB treatment outcomes. Chronic hyperglycemia impairs innate and adaptive immune responses, particularly macrophage and T-cell function, facilitating reactivation of latent infection and severe disease progression.

Conversely, tuberculosis worsens glycemic control due to stress-induced hyperglycemia, systemic inflammation, increased counter-regulatory hormones, and drug interactions with anti-diabetic therapy.

The coexistence of both diseases leads to:

• Delayed sputum conversion

• Higher relapse rates

• Higher mortality

• Increased multidrug-resistant TB (MDR-TB)

• Atypical clinical presentation

• Increased risk of metabolic emergencies (DKA and HHS)

Risk Factors

Patient-related

• Poor glycemic control (HbA1c > 8%)

• Long duration diabetes (>5 years)

• Malnutrition

• Obesity with insulin resistance

• Chronic kidney disease

• HIV co-infection

• Smoking

• Alcohol abuse

• Advanced age

Environmental / Exposure

• Living in TB endemic areas

• Household TB contact

• Crowded living conditions

• Low socioeconomic status

Disease-related

• Latent TB infection

• Immunosuppression

• Use of corticosteroids

• Previous TB infection

Signs and Symptoms

Tuberculosis symptoms (may be atypical in diabetes)

• Chronic cough (>2 weeks)

• Hemoptysis

• Fever (often low-grade)

• Night sweats

• Weight loss (may be severe)

• Fatigue

Diabetes symptoms worsening during TB

• Polyuria

• Polydipsia

• Blurred vision

• Unexplained hyperglycemia

• Recurrent infections

• Ketoacidosis or hyperosmolar state in severe cases

Atypical features in diabetics

• Lower lobe infiltrates

• Extensive cavitary disease

• Minimal respiratory symptoms despite severe radiology

• Rapid clinical deterioration

Diagnostic Criteria

Screening recommendations

• All TB patients → screen for diabetes

• All diabetic patients with chronic cough → screen for TB

Diagnosis of Tuberculosis

Any of the following:

• Positive sputum smear microscopy (AFB)

• Positive GeneXpert MTB/RIF

• Positive culture for Mycobacterium tuberculosis

• Compatible chest X-ray with clinical features

Diagnosis of Diabetes

Any one:

• Fasting plasma glucose ≥ 7.0 mmol/L

• Random plasma glucose ≥ 11.1 mmol/L with symptoms

• HbA1c ≥ 6.5%

• 2-hour OGTT ≥ 11.1 mmol/L

Investigations

For Tuberculosis

• Sputum microscopy (AFB)

• GeneXpert MTB/RIF

• TB culture

• Chest X-ray

• Full blood count

• ESR / CRP

For Diabetes

• Fasting blood glucose

• Random blood glucose

• HbA1c

• Urine ketones (if severe hyperglycemia)

• Renal function tests

Monitoring during treatment

• Monthly blood glucose

• Liver function tests

• Weight monitoring

• Sputum conversion at 2 months

Management

General Principles

• Treat both diseases simultaneously

• Tight glycemic control improves TB outcomes

• Insulin is preferred therapy during active TB

• Adjust anti-diabetic drugs due to drug interactions

Drug Interaction Considerations

Rifampicin

• Induces hepatic enzymes

• Reduces effectiveness of oral hypoglycemic agents

• Shortens sulfonylurea half-life

Isoniazid

• Causes hyperglycemia

• Reduces insulin secretion

• Increases insulin requirement

Therefore:➡ Increase anti-diabetic medication doses or switch to insulin

Non-Pharmacological Management

• Nutritional rehabilitation (high protein, adequate calories)

• Glycemic diet control

• Physical activity when stable

• Smoking cessation

• Alcohol avoidance

• Adequate sleep and stress reduction

• Infection control measures

Pharmacological Management

Tuberculosis Treatment

Standard anti-TB therapy (6 months regimen):

Intensive phase (2 months)

• Rifampicin

• Isoniazid

• Pyrazinamide

• Ethambutol

Continuation phase (4 months)

• Rifampicin

• Isoniazid

Diabetes Treatment During TB

Preferred therapy

Insulin — treatment of choice

Reasons:

• Better glycemic control

• No interaction with TB drugs

• Suitable in weight loss and catabolic state

• Safe in liver dysfunction

Oral agents (use cautiously)

• Metformin — avoid if hepatic dysfunction or severe weight loss

• Sulfonylureas — reduced effect due to rifampicin

• TZDs — avoid in liver disease

Monitoring

• Daily glucose during hospitalization

• Weekly outpatient glucose initially

• Monthly HbA1c review

• Monitor hypoglycemia after TB improvement

Prevention

Prevent TB in Diabetes

• Good glycemic control

• Screening for latent TB in high-risk patients

• Isoniazid preventive therapy when indicated

• Vaccination (BCG in endemic settings)

• Nutrition optimization

Prevent Diabetes Complications during TB

• Early insulin initiation

• Patient education

• Regular follow-up

• Weight monitoring

Key Clinical Message