Assessment of pulmonary function test in type 2 diabetes mellitus and its relation to glycaemic control and duration of disease

Background Diabetes mellitus is a metabolic disease that affects many systems and is marked by extensive vascular problems. One large microvascular bed that may be vulnerable to diabetic microangiopathy is the pulmonary alveolar–capillary network. This study aimed to assess pulmonary function in patients with type 2 diabetes mellitus (T2DM) and to examine its association with glycaemic control and disease duration. Methods This cross-sectional observational study was conducted at Ain Shams University Hospitals between February 2025 and February 2026. A total of 150 participants were enrolled, including 50 patients with controlled T2DM (HbA1c ≤ 7%), 50 patients with uncontrolled T2DM (HbA1c > 7%), and 50 age-matched healthy controls. Participants were recruited from both outpatient and inpatient settings. Data collection included fasting blood glucose, 2-hour postprandial glucose, HbA1c levels, and pulmonary function tests (PFTs). Results Baseline demographic characteristics, including age, sex, and body mass index, were comparable among groups. Pulmonary function parameters including FEV1, FVC, FEF25, FEF50, and FEF25–75 were significantly reduced in the uncontrolled T2DM group. Although FEV1/FVC showed an overall significant difference among groups, post-hoc analysis demonstrated that this was mainly driven by differences between diabetic groups and healthy controls. HbA1c showed weak-to-moderate negative correlations with several spirometric indices, particularly FEV1, FVC, FEF25, and FEF50, while longer diabetes duration was also associated with reduced pulmonary function. Multiple regression analysis identified HbA1c as the strongest independent predictor of pulmonary function decline. Conclusion Uncontrolled T2DM was associated with lower spirometric parameters in this study. However, because comprehensive pulmonary function testing including lung volumes and diffusion capacity was not performed, the nature of the ventilatory abnormality cannot be definitively determined. These findings may support a potential role for pulmonary function assessment in selected patients with T2DM and warrant further longitudinal evaluation.