Hemodynamic relevance of intermediate grade coronary stenoses is accurately assessed by fractional flow reserve (FFR) measurements. However, the reliability of FFR in patients with type 2 diabetes mellitus (DM) and inadequate glucose control (IGC) is incompletely explored. This study aimed to investigate the impact of DM and IGC on the relationship between FFR measurements and quantitative coronary angiography (QCA)-derived morphological parameters.

We performed FFR and QCA in 266 intermediate grade lesions of 224 patients (113 non-DM and 111 DM) with stable coronary artery disease. Diabetic patients were categorized into groups with adequate (Hb_A1C <7 %) and inadequate (Hb_A1c ≥7 %) glucose control.

Intermediate grade lesions from all-DM versus non-DM patients differed significantly in lesion length (LL) (10.91 ± 5.79 mm versus 9.23 ± 3.85 mm, p = 0.005) and hemodynamic relevance (FFR ≤0.8, 37.7 % versus 24.2 %, p = 0.018). FFR measurements in non-DM, all-DM and DM-IGC patients correlated significantly with percent diameter stenosis (%DS) [non-DM: r ² = 0.075 (p = 0.007); all-DM: r ² = 0.254 (p < 0.001), DM-IGC: r ² = 0.301 (p < 0.001)] and LL [non-DM: r ² = 0.356; all-DM: r ² = 0.580, DM-IGC: r ² = 0.513 (all p < 0.001)]. There was a better correlation between FFR and both %DS (p = 0.022) and LL (p = 0.011) among all-DM compared to non-DM patients. Receiver-operating curve analysis demonstrated that among all QCA-derived parameters LL had the best diagnostic efficacy to predict FFR ≤0.8 for non-DM (AUC 0.911, 95 % CI 0.861–0.960, best cut-off value 9.22 mm), all-DM (AUC 0.967, 95 % CI 0.942–0.991, best cut-off value 9.97 mm) and DM-IGC (AUC 0.960, 95 % CI 0.920–0.999, best cut-off value 9.97 mm) patients.

Our data in intermediate grade lesions suggest that FFR is reliable in DM patients and LL is the best predictor for hemodynamic relevance in patients without and with diabetes, irrespective of the glycemic state.