Malnutrition is a critical prognostic factor associated with a higher risk of in-hospital mortality in many diseases, including autoimmune disease, cardiovascular diseases, lung diseases, and malignancies.1, 2, 3, 4, 5 Numerous studies demonstrate that malnutrition among critically ill patients can reach 70 % and is substantially associated with death, length of stay in the hospital, and time spent on mechanical ventilation.6, 7, 8, 9 A systematic review found that 49.1 % of hospitalized patients with COVD-19 were malnourished, and their mortality risk was 10 times higher than that of well-nourished patients.6 Currently, there is no standard nutritional screening tool or specific method for assessing nutritional status in patients with COVID-19.10

The prognostic nutritional index (PNI) assesses nutritional status through serum albumin levels and immune function via lymphocyte counts, objectively evaluating disease severity and helping to reduce adverse outcomes.11 The dysregulation of immune response and inflammation plays a crucial role in developing COVID-19.12,13 There is a strong association between high levels of malnutrition and increased inflammation, emphasizing the importance of malnutrition risk screening and its prognostic value for COVID-19 patients.14, 15, 16 Various inflammatory markers, including C-reactive protein (CRP), hypoalbuminemia, neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR) have been linked to disease severity and higher mortality rates in COVID-19 patients.17, 18, 19, 20 The PNI quantifies immune status and may help to indicate the severity of COVID-19.21, 22, 23 It is also a predictor of mortality in hospitalized COVID-19 patients.24 The PNI can be derived from basic routine assessments for every patient and serves as a valuable clinical marker, even in settings with limited resources. Most studies evaluating the PNI were conducted at a single center outside the United States.

We aimed to evaluate whether the PNI was independently associated with the severity of COVID-19 infection among hospitalized patients in the United States within a multicenter historical cohort.