Hypochloremia: A Potential Indicator of Poor Outcomes in COVID-19

<i>Background: Coronavirus</i> Disease-2019 (COVID-19) has posed formidable challenges to healthcare systems. Exploring novel biomarkers that can provide valuable prognostic insights, particularly in critically ill patients, has a significant importance. Against this backdrop, our study aims to elucidate the associations between serum chloride levels and clinical outcomes. <i>Methods:</i> A total of 499 patients were enrolled into the study. The serum chloride levels of patients upon hospital admission were recorded and then categorized into three groups (hypochloremia, normochloremia, and hyperchloremia) for the evaluation of clinical outcomes. Additionally, serum C-reactive protein, procalcitonin, and D-dimer measurements were recorded for further evaluation. <i>Results:</i> A total of 390 (78.1%) patients tested positive for COVID-19 via polymerase chain reaction testing. Non-contrast thorax computed tomography scans were indicative of COVID-19 compatibility for all patients. A total of 210 (42%) patients were female and 289 (58%) were male. A total of 214 (42.8%) patients necessitated tocilizumab intervention; 250 (50.1%) were at an intensive care unit (ICU), with 166 (66.4%) of them receiving tocilizumab. A total of 65 (13%) patients died, 40 (61.5%) of whom received tocilizumab; 41 (63%) were in the ICU. Serum chloride levels upon admission were markedly lower and elevated D-dimer levels were apparent in tocilizumab users, patients requiring ICU care, and patients who died. <i>Conclusions:</i> our findings provide robust evidence supporting the value of serum chloride levels as a prognostic biomarker in critically ill COVID-19 patients.