# Clinical significance of cytokeratin 19 fragment in COVID-19 patients: a retrospective study

## TL;DR

This study found that elevated levels of CYFRA 21-1, a lung cancer biomarker, are linked to both the diagnosis and severity of COVID-19 pneumonia.

## Contribution

The study is the first to investigate the clinical significance of CYFRA 21-1 in patients with COVID-19 pneumonia.

## Key findings

- CYFRA 21-1 levels increased progressively with the severity of COVID-19 pneumonia.
- CYFRA 21-1 was identified as an independent diagnostic and prognostic factor for COVID-19 pneumonia.
- CYFRA 21-1 showed a strong negative correlation with the oxygenation index in severe cases.

## Abstract

Cytokeratin 19 fragment (CYFRA 21-1) is an important biomarker of lung cancer. There are clinical observations of elevated serum levels of lung cancer biomarkers in patients with viral pneumonia. However, the clinical significance of CYFRA 21-1 in coronavirus disease 2019 pneumonia has not been investigated.

This retrospective study included 252 patients with community-acquired pneumonia (CAP) between December 1, 2022, and September 30, 2023. They were classified into three groups by clinical diagnosis and severity, namely mild non-COVID-19 CAP (n = 86), mild COVID-19 (n = 100), and severe COVID-19 (n = 66). Demographic characteristics, history, outcomes, and laboratory tests, including CYFRA 21-1 levels, were collected and compared among the groups. Risk factors associated with the diagnosis of COVID-19 pneumonia and severity were explored using appropriate statistical methods.

CYFRA 21-1 levels progressively increased from mild non–COVID-19 CAP to mild COVID-19 and severe COVID-19. Lower lymphocyte and platelet counts, alongside elevated CYFRA 21-1 levels, were associated with COVID-19 pneumonia. Multivariate analysis identified CYFRA 21-1 as an independent diagnostic [diagnosis odds ratio (OR) = 2.369; 95% confidence interval (CI) = 1.638–3.605; p < 0.001] and prognosis factor of COVID-19 pneumonia (severity OR = 1.416; 95% CI = 1.119–1.867; p = 0.01). The area under the receiver operating characteristic curve of CYFRA 21-1 for predicting the development of severe COVID-19 pneumonia was 0.913. Spearman analysis showed a negative correlation between CYFRA 21-1 levels and oxygenation index, with a correlation coefficient of −0.278 (p = 0.024).

CYFRA 21-1 may be a potential diagnostic and prognostic indicator of COVID-19 pneumonia. Prospective multicenter studies are needed to confirm its clinical value.