Korean J Intern Med.  2025 Mar;40(2):321-329. 10.3904/kjim.2024.161.

Initial and peak serum levels of Krebs von den Lungen-6 for predicting the prognosis of patients with COVID-19

• Kim G
• Kwon H
• Ra SH
• Chang E
• Bae S
• Jung J
• Kim MJ
• Chong YP
• Lee SO
• Choi SH
• Kim YS
• Kim SH

• KMID: 2567108
• DOI: http://doi.org/10.3904/kjim.2024.161

Abstract

Background/Aims
Krebs von den Lungen-6 (KL-6) is associated with prognosis in patients with COVID-19. However, there is limited data on the correlation between the prognosis of COVID-19 and varying KL-6 levels at different time points. We investigated the optimal cutoff values of the initial and peak serum KL-6 levels to predict mortality and evaluated their correlation with mortality.
Methods
This retrospective cohort study collected data on serially collected serum KL-6 levels in patients hospitalized with COVID-19 between October 2020 and January 2022 at a single tertiary hospital in South Korea. The area under the receiver operating characteristic curve and Youden index were used to determine the cutoff points for the initial and peak KL-6 levels that best predicted 30-day mortality. The association between the initial and peak KL-6 values was assessed by univariate and multivariate logistic regression models.
Results
A total of 349 patients were included in this study. The mean initial and peak KL-6 levels were significantly higher in the non-survivor group than in the survivor group. The initial and peak KL-6 values that best predicted 30-day mortality were 491.85 U/mL and 660.05 U/mL, respectively. An initial KL-6 level greater than 491.85 U/mL and a peak KL-6 level greater than 660.05 U/mL were significantly associated with 30-day mortality.
Conclusions
The initial and peak levels of KL-6 were significantly associated with 30-day mortality in hospitalized patients with COVID-19. These findings suggest that serially monitoring blood KL-6 levels could be a valuable prognostic indicator for COVID-19.

Keyword

KL-6 antigen; COVID-19; Prognosis