Subject selection
Study subjects were recruited from Aga Khan University and Hospital (AKUH), Karachi, Pakistan using a cross-sectional study design with a consecutive convenience sampling method. Study subjects were recruited within a given study period based on the given inclusion criteria.
All study subjects were aged 18 – 65 years. Thirty-nine asymptomatic healthy volunteers at AKUH were recruited for the study. We recruited health care workers who have contact with TB patients as possible LTB cases in addition to household contacts of TB patients. Thirty-three patients with DM were recruited from Department of Medicine clinics. Inclusion criteria for DM cases were: patients with previously confirmed Type 2 DM. Exclusion criteria were pregnancy, comorbid conditions such as HIV infection, active TB, chronic renal failure, chronic liver disease or corticosteroid therapy. For potential DM-LTBi cases we recruited household contacts of TB patients who had DM.
In total, ten ml of whole blood sample was drawn from all study subjects. Random blood glucose (RBS) and glycosylated hemoglobin (HbA1c) levels were tested. DM was defined by HbA1c ≥ 6.4 %.
A positive reaction in a Quantiferon TB Gold in Tube assay (QFT-GIT) test was performed to classify individuals which are otherwise are healthy and asymptomatic as LTBi. As per manufacturer’s instructions, a threshold of ≥0.35 IU/mL was considered for LTBi. Hence after QFT-GIT testing, the healthy control group was categorized into endemic controls (EC n=24) or latent TB cases (LTBi, n=15). Further, subjects recruited in the DM group were further categorized into QFT-GIT negative (DM, n=16) and positive (DM-LTBi, n=17).
Fifteen patients with pulmonary TB (PTB) were recruited. Patients with confirmed diagnosis of TB who had not received anti-tuberculous therapy (ATT); male or female; between 18–65 years of age were included in the study. Exclusion criteria were pregnancy, comorbid conditions (such as HIV infection, DM, chronic renal failure, chronic liver disease or corticosteroid therapy) and patients with relapsed TB. All PTB patients were diagnosed by clinical examination, chest X-ray and had a positive sputum acid-fast bacillus (AFB) microscopy and/ or AFB culture. They were classified as PTB as per WHO guidelines (25).