AbstractTo assess the association between low serum creatinine (SCr) value at admission and the risk of respiratory failure requiring mechanical ventilation in hospitalized patients. A retrospective cohort study was conducted at a tertiary referral hospital. All hospitalized adult patients from 2011 through 2013 who had an admission SCr value were included in this study. Patients who were mechanically ventilated at the time of admission were excluded. Admission creatinine was stratified into 7 groups: ≤0.4, 0.5–0.6, 0.7–0.8, 0.9–1.0, 1.1–1.2, 1.3–1.4, and ≥1.5 mg/dL. The primary outcome was the occurrence of respiratory failure requiring mechanical ventilation during hospitalization. Logistic regression analysis was used to assess the independent risk of respiratory failure based on various admission SCr, using SCr of 0.7–0.8 mg/dL as the reference group in the analysis of all patients and female subgroup and of 0.9–1.0 mg/dL in analysis of male subgroup. A total of 67,045 eligible patients, with the mean admission SCr of 1.0 ± 0.4 mg/dL, were studied. Of these patients, 799 (1.1%) had admission SCr of ≤0.4 mg/dL, and 2886 (4.3%) developed respiratory failure requiring mechanical ventilation during hospitalization. The U-curve relationship between admission SCr and respiratory failure during hospitalization was observed, with the nadir incidence of in-hospital respiratory failure in SCr of 0.7–0.8 mg/dL and increased in-hospital respiratory failure associated with both reduced and elevated admission SCr. After adjustment for confounders, very low admission SCr of ≤0.4 mg/dL was significantly associated with increased in-hospital respiratory failure (OR 3.11; 95% CI 2.33–4.17), exceeding the risk related to markedly elevated admission SCr of ≥1.5 mg/dL (OR 1.61; 95% CI 1.39–1.85). The association remained significant in the subgroup analysis of male and female patients. Low SCr value at admission is independently associated with increased in-hospital respiratory failure requiring mechanical ventilation in hospitalized patients.