Further subgroup analyses for the risk of HHF was performed according to baseline CKD (Additional file 1: Table S3), history of TZD use (Additional file 1: Table S4 and Table S5) and stratified by individual DPP4 inhibitors (Additional file 1: Table S6), which resulted in similar findings of DPP4i-associated increased risk of HHF. This evidence concerns the gene DPP4 and chronic kidney disease.