Predictive value of D‐dimer levels for 30‐day mortality and hospital length of stay in patients admitted for coronavirus disease of 2019 during the 5th wave in Hong Kong, a retrospective cohort study

Abstract Background Elevated D‐dimer levels are associated with increased disease severity and mortality in coronavirus disease 2019 (COVID‐19) patients, but its predictive value in Hong Kong's Omicron‐predominant fifth wave remains unstudied, especially among hospitalized high risk patient groups. This study evaluates the predictive utility of D‐dimer levels measured within 72 h of admission for 30‐day in‐hospital mortality, length of stay (LOS), intensive care unit (ICU) admission and need for mechanical ventilation in COVID‐19 patients at Kwong Wah Hospital. Methods This retrospective cohort study included 435 adult inpatients (mean age 78.6 years, 60.2% male) with laboratory‐confirmed COVID‐19 admitted via the Accident and Emergency (A&E) department from March 1–31, 2022. D‐dimer levels, demographics, comorbidities, LOS, ICU admission, need for mechanical ventilation and 30‐day mortality were extracted from electronic records. Statistical analyses included bivariate comparisons, binary logistic regression and Fine‐Gray subdistribution hazards model, and receiver operating characteristic (ROC) analysis to determine an optimal D‐dimer threshold. Results The 30‐day mortality rate was 37.7% ( n = 164), with a mean LOS of 13.3 days. Higher D‐dimer levels were associated with increased mortality (median 2.5 vs. 1.4 μg/mL, p < 0.001), ICU admission (odds ratio (OR) 1.31), mechanical ventilation (OR = 3.85) and prolonged hospitalization ( p < 0.001, Subdistribution hazard ratio = 0.82). Each 1 μg/mL increase in D‐dimer raised mortality odds by 28% (OR 1.28, 95%). Age and male gender were also associated with mortality ( p < 0.05). An ROC analysis of the dataset identified a D‐dimer threshold of 1.864 μg/mL (AUC 0.68, p < 0.001) for predicting mortality with an OR of 3.52 ( p < 0.001). Conclusion In adult inpatients with COVID‐19 during Hong Kong's fifth wave, elevated D‐dimer within 72 h of admission significantly increased 30‐day in‐hospital mortality, LOS, ICU admission and need for mechanical ventilation. Routine D‐dimer testing at the A&E department may aid early risk stratification and streamline patient care.