BackgroundThe renin-angiotensin-aldosterone system was shown to be activated in severe COVID-19 infection. We aimed to investigate the relationship between angiotensin converting enzyme (ACE) levels,ACEgene polymorphism, type 2 diabetes (T2DM), and hypertension (HT) and the prognosis of COVID-19 infection.MethodsThis cross-sectional study analyzed the clinical features of adult patients with SARS-CoV-2 infection.ACEgene analysis and ACE level measurements were performed. The patients were grouped according toACEgene polymorphism (DD, ID or II), disease severity (mild, moderate, or severe), and the use of dipeptidyl peptidase-4 enzyme inhibitor (DPP4i), ACE-inhibitor (ACEi) or angiotensin receptor blocker (ARB). Intensive care unit (ICU) admissions and mortality were also recorded.ResultsA total of 266 patients were enrolled. Gene analysis detected DD polymorphism in theACE 1gene in 32.7% (n = 87), ID in 51.5% (n = 137), and II in 15.8% (n = 42) of the patients.ACEgene polymorphisms were not associated with disease severity, ICU admission, or mortality. ACE levels were higher in patients who died (p = 0.004) or were admitted to the ICU (p<0.001) and in those with severe disease compared to cases with mild (p = 0.023) or moderate (p<0.001) disease. HT, T2DM, and ACEi/ARB or DPP4i use were not associated with mortality or ICU admission. ACE levels were similar in patients with or without HT (p = 0.374) and with HT using or not using ACEi/ARB (p = 0.999). They were also similar in patients with and without T2DM (p = 0.062) and in those with and without DPP4i treatment (p = 0.427). ACE level was a weak predictor of mortality but an important predictor of ICU admission. It predicted ICU admission in total (cutoff value >37.092 ng/mL, AUC: 0.775, p<0.001).ConclusionOur findings suggest that higher ACE levels, but notACEgene polymorphism, ACEi/ARB or DPP4i use, were associated with the prognosis of COVID-19 infection. The presence of HT and T2DM and ACEi/ARB or DPP4i use were not associated with mortality or ICU admission.