Serum surfactant protein D as a biomarker for measuring lung involvement in obese patients with type 2 diabetes

Abstract

Context: Lung impairment is a new target for late diabetic complications. Biomarkers that could help identify patients requiring functional respiratory tests have not been reported. Objective: Our aim was to examine whether serum surfactant protein D (SP-D) and A (SP-A) could be useful biomarkers of lung damage in obese patients with type 2 diabetes (T2D) without known lung disease. Design and Setting: A case-control study conducted in an ambulatory obesity unit. Patients: Forty-nine obese patients with T2D and 98 subjects without diabetes matched by age, sex, body mass index, and waist circumference were included. Interventions: Serum SP-D and SP-A levels were measured using enzyme-linked immunosorbent assay. Forced spirometry and static pulmonary volume were assessed. Results: Patients with T2D exhibited higher serum SP-D concentrations than control subjects (P = 0.006). No differences in serum SP-A concentrations were observed. There was an inverse association between forced expiratory volume in 1 second (FEV1) and serum SP-D (r = 20.265; P = 0.029), as well as a significant positive relationship between SP-D concentration and residual volume (r = 0.293; P = 0.043). From receiver operating characteristic analysis, the best SP-D cutoff to identify a FEV1, 80% of predicted was 132.3 ng/mL (area under the curve, 0.725; sensitivity, 77.7%; specificity, 69.4%). Stepwise multivariate regression analysis showed that serum SP-D concentration ≥132.3 ng/mL was independently associated with a FEV1, 80% of predicted (R2 = 0.406). Only the existence of T2D contributed independently to serum SD-P variance among all subjects (R2 = 0.138). Conclusions: Serum SP-D concentration can be a useful biomarker for detecting lung impairment in obese patients with T2D.