Diagnostic value of KL-6 in idiopathic interstitial pneumonia

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

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.

CONCLUSION

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.

Krebs von den Lungen-6 surveillance in immune checkpoint inhibitor-induced pneumonitis

BACKGROUND

The immune-related adverse event (irAE), pneumonitis, is a potentially fatal complication of immune checkpoint inhibitors (ICIs). Preventing its progression is crucial, emphasizing the need for effective screening tests. We evaluated the feasibility of using Krebs von den Lungen-6 (KL-6), a marker for interstitial pneumonitis, as a screening tool for pneumonitis.

METHODS

We examined 500 patients with cancer divided into two groups: those with cancer other than non-small cell lung cancer (NSCLC) (Group 1, n=382) and those with NSCLC (Group 2, n=118). KL-6 levels were monitored before and during ICI treatment and analyzed for their correlation with pneumonitis.

RESULTS

In Group 1, 37 patients (9.7%) developed pneumonitis. KL-6 levels were significantly elevated at irAE onset (pre: 222.0 U/mL, post: 743.0 U/mL, p<0.0001). Receiver operating characteristic curve analysis showed an area under the curve (AUC) of 0.903 (sensitivity 81.1%, specificity 91.6%) with a cut-off value 1.52 times pre-KL-6 levels, indicating that KL-6 is a reliable biomarker for pneumonitis. In these patients, the KL-6 level increased regardless of pneumonitis severity and was significantly elevated in patients with both symptomatic (pre: 205.0 U/mL, post: 674.5 U/mL, p<0.0001) and asymptomatic pneumonitis (pre: 314.0 U/mL, post: 743.0 U/mL, p<0.0001) at irAE onset. After irAE treatment, KL-6 levels in steroid-responsive patients remained unchanged; however, steroid-unresponsive patients had a significant increase in KL-6 levels at 1 month (1078 U/mL, p=0.031) compared with at irAE onset (678.0 U/mL). In Group 2, 24 patients (20.3%) developed irAE pneumonitis, with KL-6 levels elevated (pre: 360.5 U/mL, post: 506.5 U/mL, p=0.029) and an AUC of 0.683, indicating that KL-6 was less reliable in patients with NSCLC.

CONCLUSIONS

KL-6 is a viable screening biomarker in ICI-induced pneumonitis, particularly in patients without NSCLC. In patients with NSCLC, the significance of KL-6 monitoring is limited as it is not effective for detecting ICI-induced pneumonitis; their treatment is typically managed by pulmonary specialists. Early detection through KL-6 monitoring facilitates timely intervention for ICI-induced pneumonitis, potentially preventing treatment interruptions and reducing the need for immunosuppressants.

Safety and effectiveness of certolizumab pegol in Japanese patients with rheumatoid arthritis: Up to 3-year results from a postmarketing surveillance study

OBJECTIVES

To report up to 3-year safety and effectiveness of certolizumab pegol (CZP) in Japanese patients with rheumatoid arthritis from a postmarketing surveillance study.

METHODS

Patients enrolled previously completed 24 weeks of CZP in the 24-week postmarketing surveillance study. Adverse drug reactions (ADRs) were recorded for patients who received ≥1 CZP dose. Effectiveness outcomes were 28-joint Disease Activity Score with erythrocyte sedimentation rate and European Alliance of Associations for Rheumatology response. Week 24-156 safety and Week 0-52 effectiveness data are reported here.

RESULTS

A total of 781 patients were enrolled, with 735 and 376 patients evaluated for safety and effectiveness, respectively. Within the safety set, 17.8% (131/735) of patients reported ADRs; 9.4% (69/735) reported serious ADRs. Among patients with history of respiratory, thoracic, and mediastinal disorders, 38.4% (28/73) reported ADRs. The most frequent ADRs were infections and infestations (11.8%; 87/735); skin and subcutaneous tissue disorders (1.9%; 14/735); respiratory, thoracic, and mediastinal disorders (1.6%; 12/735). Mean 28-joint Disease Activity Score with erythrocyte sedimentation rate reduced from 4.6 (Week 0) to 2.8 (Week 52). At Week 52, 51.8% (161/311) of patients achieved European Alliance of Associations for Rheumatology Good response.

CONCLUSIONS

The long-term safety and effectiveness of CZP in the real-world setting in Japan were consistent with previously reported data; no new safety signals were identified.

Amiodarone Therapy: Updated Practical Insights

Amiodarone, a bi-iodinated benzofuran derivative, is among the most commonly used antiarrhythmic drugs due to its high level of effectiveness. Though initially categorized as a class III agent, amiodarone exhibits antiarrhythmic properties across all four classes of antiarrhythmic drugs. Amiodarone is highly effective in maintaining sinus rhythm in patients with paroxysmal atrial fibrillation while also playing a crucial role in preventing a range of ventricular arrhythmias. Amiodarone has a complex pharmacokinetic profile, characterized by a large volume of distribution and a long half-life, which can range from several weeks to months, resulting in prolonged effects even after discontinuation. Side effects may include thyroid dysfunction, pulmonary fibrosis, and hepatic injury, necessitating regular follow-ups. Additionally, amiodarone interacts with several drugs, including anticoagulants, which must be managed to prevent adverse effects. Therefore, a deep understanding of both oral and intravenous formulations, as well as proper dosage adjustments, is essential. The aim of this paper is to provide a comprehensive and updated review on amiodarone's indications, contraindications, recommended dosages, drug interactions, side effects, and monitoring protocols.

CA 15 - 3 in screening for systemic autoimmune rheumatic disease associated interstitial lung disease: a single center cross-sectional study

INTRODUCTION

The natural course of interstitial lung disease (ILD) in patients with systemic autoimmune rheumatic diseases (SARD) varies significantly and is linked to considerable morbidity and mortality. Therefore, effective screening is crucial for early detection of SARD-ILD. Biomarkers associated with mucin 1, Krebs von den Lungen-6 (KL-6) and carbohydrate antigen 15-3 (CA 15-3), are increased in various ILD. This study aimed to assess the diagnostic accuracy of the serum biomarker CA 15-3 as a potential screening tool for ILD in patients newly diagnosed with SARD.

METHODS

Conducted as a single-center cross-sectional study, the research included newly diagnosed SARD patients consecutively examined for ILD according to the algorithm. All included patients underwent chest high-resolution CT scans (HRCT), and serum levels of CA 15-3, KL-6, and lactate dehydrogenase (LDH) were measured and correlated with other variables associated with possible ILD presence.

RESULTS

Serum biomarker levels, specifically CA 15-3 and LDH, are significantly higher in ILD-positive patients (P<0.001 for both). An inverse relationship is observed between higher FVC values and lower CA 15-3 levels (Rho=-0.291, P=0.007). Similarly, higher DLCO values are associated with lower CA 15-3 levels (Rho=-0.317, P=0.003). Our findings revealed that elevated CA 15-3 levels are positively correlated with higher levels of KL-6 (Rho=0.268, P=0.01) and LDH (Rho=0.227, P=0.04). With a cut-off value of 24 U/mL, CA 15-3 showed the highest sensitivity and specificity (AUC=0.807, specificity=95.7%, sensitivity=71.1%). CA 15-3 emerged as the most significant predictor of a positive HRCT finding, accurately classifying 83% of cases.

CONCLUSION

These results suggest that CA 15-3 shows promise as a valuable serum biomarker for screening SARD patients for ILD in routine clinical practice.

An in-depth investigation of serum Krebs von den Lungen-6 and other biomarkers in COVID-19 severity and mortality

Krebs von den Lungen-6 (KL-6) is a glycoprotein mainly expressed by type II pneumocytes and recently known as a lung injury biomarker. However, the number of studies is still limited, especially in Indonesian COVID-19 populations. Therefore, we aim to provide correlation, sensitivity, and specificity analyses of KL-6 and other biomarkers in Indonesian COVID-19 severity and mortality. We conducted a cross-sectional study involving adult COVID-19 patients at Universitas Airlangga Hospital, Surabaya, East Java, Indonesia, between March 26, 2021, and August 25, 2021. KL-6 and other biomarker levels were compared according to severity (severe versus non-severe) and mortality (non-survivor versus survivor). We also included the receiver operating characteristic analysis to define the optimal cut-off, sensitivity, and specificity of KL-6 to determine COVID-19 severity and mortality. We enrolled 78 COVID- 19 patients (23 non-survivors), including 39 non-severe and 39 severe patients. There was no significant difference in serum KL-6 levels, neither in severity nor mortality groups. KL-6 had the strongest positive correlations with ferritin in severe patients (r=0.313) and non-survivors (r=0.467). We observed that the best sensitivity was KL-6 combined with platelet-to- lymphocyte ratio (PLR) (0.818) in severe patients and with neutrophil-to-lymphocyte ratio (NLR)/PLR/ferritin/C-reactive protein (0.867) in non-survivors. In contrast, the best specificity was found when KL-6 was combined with NLR/D-dimer (0.750) in severe patients and with D-dimer (0.889) in non-survivors. Serum KL-6 is a useful auxiliary laboratory evaluation index for COVID-19 lung injury to depict its severity and mortality.

Diagnostic Value of Krebs von den Lungen (KL-6) for Interstitial Lung Disease: A European Prospective Cohort

INTRODUCTION

Krebs von den Lungen 6 (KL-6) is a mucin-1 glycoprotein produced by type II pneumocytes. High levels of KL-6 in blood may be found in patients with lung fibrosis. In Asia this biomarker is used for diagnosis and prognosis in interstitial lung diseases (ILD). There is a lack of information regarding KL-6 cut-off point for diagnosis and prognosis in European population. The aim of this study was to establish the cut-off point for serum KL-6 associated with the presence of ILD in the Spanish population.

METHODS

Prospective study including subjects who underwent chest HRCT, PFTs and autoimmune blood analysis. Two groups were created: non-ILD subjects and ILD patients. Serum KL-6 concentrations were measured using a Lumipulse KL-6 reagent assay and the optimal cut-off value was evaluated by a ROC analysis. Data on demographics and smoking history was also collected.

RESULTS

One hundred seventy-nine patients were included, 102 with ILD. Median serum KL-6 values overall were 762U/mL, 1080 (±787)U/mL for the ILD group vs 340 (±152)U/mL for the non-ILD group (p<0.0001). The main radiological pattern was NSIP (43%). ROC analysis showed greater specificity (86%) and sensitivity (82%) for KL-6 465U/mL for detecting ILD patients. The multivariate logistic regression model pointed to the male sex, higher KL-6 values, lower FVC and low DLCO values as independent factors associated with ILD.

CONCLUSION

Serum KL-6 values greater than 465U/mL have excellent sensitivity and specificity for detecting ILD in our Spanish cohort. Multicentre studies are needed to validate our results.

Clinical characteristics and outcome of lung cancer in patients with fibrosing interstitial lung disease

BACKGROUND

Lung cancer (LC) is an important comorbidity of interstitial lung disease (ILD) and has a poor prognosis. The clinical characteristics and outcome of each ILD subtype in LC patients have not been sufficiently investigated. Therefore, this study aimed to evaluate the difference between idiopathic pulmonary fibrosis (IPF) and non-IPF ILD as well as prognostic factors in patients with ILD-LC.

METHODS

The medical records of 163 patients diagnosed with ILD-LC at Asan Medical Center from January 2018 to May 2023 were retrospectively reviewed. Baseline characteristics and clinical outcomes were compared between the IPF-LC and non-IPF ILD-LC groups, and prognostic factors were analyzed using the Cox proportional-hazard model.

RESULTS

The median follow-up period was 11 months after the cancer diagnosis. No statistically significant differences were observed in clinical characteristics and mortality rates (median survival: 26 vs. 20 months, p = 0.530) between the groups. The independent prognostic factors in patients with ILD-LC were higher level of Krebs von den Lungen-6 (≥ 1000 U/mL, hazard ratio [HR] 1.970, 95% confidence interval [CI] 1.026-3.783, p = 0.025) and advanced clinical stage of LC (compared with stage I, HR 3.876 for stage II, p = 0.025, HR 5.092 for stage III, p = 0.002, and HR 5.626 for stage IV, p = 0.002). In terms of treatment, surgery was the significant factor for survival (HR 0.235; 95% CI 0.106-0.520; p < 0.001).

CONCLUSIONS

No survival difference was observed between IPF-LC and non-IPF ILD-LC patients. A higher level of Krebs von den Lungen-6 may act as a prognostic marker in ILD-LC patients.

Plasma KL-6 as a Potential Biomarker for Bronchopulmonary Dysplasia in Preterm Infants

Background

KL-6 is a biomarker of interstitial lung injury and increases during repair.

Aim

Our aim was to determine the predictive value of plasma KL-6 for the development of bronchopulmonary dysplasia (BPD) in preterm infants.

Methods

Ninety-five extremely preterm infants (EPIs), born at <28 gestational age (GA), were divided into two main BPD groups as follows: the moderate/severe and the no/mild group. KL-6 was analyzed on days 7 and 14. Binary logistic regression analyses and ROC curve analyses were performed.

Results

Infants <26 + 0 weeks' GA have higher mean KL-6 than infants >25 + 6 weeks' GA on 7 and 14 days (335 vs. 286 U/ml and 378 vs. 260 U/ml; p = 0.005 and 0.018, respectively). In the binary regression model at KL-6 day 7, three of the prognostic factors remained significant-mechanical ventilation OR: 10.38 (95% CI: 3.57-30.14), PDA OR: 6.39 (95% CI: 0.87-46.74), and KL-6 OR: 4.98 (95% CI: 1.54-16.08). The AUC was 0.86 with a sensitivity and specificity of 79% at a cutoff value ≥0.34. In the binary regression model at KL-6 day 14, six of the prognostic factors were significant-PDA OR: 23.34 (95% CI: 2.14-254.24), KL-6 OR: 13.59 (95% CI: 3.19-57.96), GA OR: 4.58 (95% CI: 1.16-18.06), mechanical ventilation OR: 4.45 (95% CI: 1.23-16.16), antenatal steroids OR: 0.19 (95% CI: 0.04-0.95), and gender (female OR: 0.30 (95% CI 0.08-1.12)). The AUC was 0.91, and the sensitivity and accuracy for a cutoff ≥0.37 were 89% and 85%, respectively.

Conclusion

KL-6 could be a useful screening biomarker for early detection of infants at increased risk for developing BPD.

Serum KL-6 levels predict the occurrence and severity of treatment-related interstitial lung disease in lung cancer

In this study, we aimed to investigate the feasibility of serum Krebs von den Lungen-6 (KL-6) as a potential biomarker for treatment-related ILD (TR-ILD) in lung cancer. We recruited patients with lung cancer in whom KL-6 was measured to differentiate between pneumonia and ILD (category 1), diagnose and assess the severity of suspicious ILD (category 2), or evaluate baseline levels before cancer treatment (category 3). Among 1,297 patients who underwent KL-6 testing, 422 had lung cancer, and TR-ILD was detected in 195 patients. In categories 1-2, median KL-6 level was higher in drug-induced ILD or acute exacerbation of underlying ILD than in no ILD or radiation-induced pneumonitis, and it was correlated with the severity of TR-ILD. High KL-6 level (cut-off: > 436U/mL) was an independent risk factor for severe TR-ILD, and low KL-6 level with high procalcitonin level (> 0.5 ng/mL) could exclude severe TR-ILD. Patients with severe TR-ILD had worse overall survival than those without, whereas high baseline KL-6 level was associated with worse survival, especially in patients without severe TR-ILD. Therefore, serum KL-6 may be a surrogate marker for predicting the occurrence and assessing the severity of TR-ILD at the time of suspected ILD and before lung cancer treatment.

Krebs von den Lungen-6 as a Potential Predictive Biomarker in Fibrosing Interstitial Lung Diseases

BACKGROUND

As fibrosing interstitial lung diseases (fILDs) are associated with high mortality, monitoring of disease activity under treatment is highly relevant. Krebs von den Lungen-6 (KL-6) is associated with the presence and severity of different fILDs, mainly in Asian patient populations.

OBJECTIVES

Our aim was to evaluate KL-6 as a predictive biomarker in fILDs in Caucasian patients.

METHODS

Consecutive patients with fILDs were recruited prospectively and serum concentrations of KL-6 were measured at baseline (BL), after 6 and 12 months (6 Months, 12 Months). Clinical characteristics including pulmonary function tests were assessed at 6-monthly visits and correlated with KL-6 BL levels as well as with KL-6 level changes.

RESULTS

A total of 47 fILD patients were included (mean age: 65 years, 68% male). KL-6 levels at BL were significantly higher in fILD patients than in healthy controls (n = 44, mean age: 45, 23% male) (ILD: 1,757 ± 1960 U/mL vs. control: 265 ± 107 U/mL, p < 0.0001). However, no differences were noted between ILD subgroups. KL-6 decreased significantly under therapy (6M∆BL-KL6: -486 ± 1,505 mean U/mL, p = 0.032; 12M∆BL-KL6: -547 ± 1,782 mean U/mL, p = 0.041) and KL-6 level changes were negatively correlated with changes in pulmonary function parameters (forced vital capacity [FVC]: r = -0.562, p < 0.0001; DLCOSB: r = -0.405, p = 0.013). While neither absolute KL-6 levels at BL nor KL-6 level changes were associated with ILD progression (FVC decline ≥10%, DLCOSB decline ≥15% or death), patients with a stable FVC showed significantly decreasing KL-6 levels (p = 0.022).

CONCLUSIONS

A decline of KL-6 under therapy correlated with a clinically relevant stabilization of lung function. Thus, KL-6 might serve as a predictive biomarker, which however must be determined by larger prospective cohorts.

Unmet needs and perspectives in rheumatoid arthritis-associated interstitial lung disease: A critical review

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by synovitis as the most common clinical manifestation, and interstitial lung disease (RA-ILD) represents one of the most common and potentially severe extra-articular features. Our current understanding of the mechanisms and predictors of RA-ILD is limited despite the demonstration that an early identification of progressive fibrosing forms is crucial to provide timely treatment with antifibrotic therapies. While high resolution computed tomography is the gold standard technique for the diagnosis and follow-up of RA-ILD, it has been hypothesized that serum biomarkers (including novel and rare autoantibodies), new imaging techniques such as ultrasound of the lung, or the application of innovative radiologic algorithms may help towards predicting and detecting early forms of diseases. Further, while new treatments are becoming available for idiopathic and connective tissue disease-associated forms of lung fibrosis, the treatment of RA-ILD remains anecdotal and largely unexplored. We are convinced that a better understanding of the mechanisms connecting RA with ILD in a subgroup of patients as well as the creation of adequate diagnostic pathways will be mandatory steps for a more effective management of this clinically challenging entity.

Review: Serum Biomarkers of Lung Fibrosis in Interstitial Pneumonia with Autoimmune Features-What Do We Already Know?

Interstitial pneumonia with autoimmune features (IPAF) belongs to a group of diseases called interstitial lung diseases (ILDs), which are disorders of a varied prognosis and course. Finding sufficiently specific and sensitive biomarkers would enable the progression to be predicted, the natural history to be monitored and patients to be stratified according to their treatment. To assess the significance of pulmonary fibrosis biomarkers studied thus far, we searched the PubMed, Medline and Cochrane Library databases for papers published between January 2015 and June 2021. We focused on circulating biomarkers. A primary review of the databases identified 38 articles of potential interest. Overall, seven articles fulfilled the inclusion criteria. This review aims to assess the diagnostic and prognostic value of molecules such as KL-6, SP-A, SP-D, circulating fibrocytes, CCL2, CXCL13, CXCL9, CXCL10 and CXCL11. All of these biomarkers have previously been studied in idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease (CTD-ILD). IPAF is a disorder of a heterogeneous nature. It explains the lack of coherent observations in terms of correlations with functional parameters. There is still no meta-analysis of pulmonary fibrosis biomarkers in IPAF. This is mainly due to the heterogeneity of the methodology and groups analysed in the research. More research in this area is needed.

The Prognostic Value of Krebs von den Lungen-6 and Surfactant Protein-A Levels in the Patients with Interstitial Lung Disease

Background and Objectives

The highly variable clinical course of interstitial lung disease (ILD) makes it difficult to predict patient prognosis. Serum surfactant protein-A (SP-A) and Krebs von den Lungen-6 (KL-6) are known prognostic biomarkers. However, the clinical or pathophysiological differences in patients with these biomarkers have not been well evaluated. We investigated the clinical and pathophysiological differences through the comparison of SP-A and KL-6 levels before and after treatment.

Methods

This study included retrospective data from 91 patients who were treated for ILD between August 2015 and September 2019. Serum SP-A and KL-6 levels were measured before and after treatment. The patients were followed up for 3 months.

Results

Changes in the serum biomarkers (Delta SP-A and Delta KL-6) were found to be significantly correlated (rs = 0.523, P < 0.001); Delta SP-A and Delta KL-6 were inversely correlated with changes in pulmonary function (% predicted values of diffusing capacity for carbon monoxide [DLCO], forced vital capacity [FVC], and forced expiratory volume in 1 s [FEV1]). Patients were divided into four groups based on their Delta SP-A and Delta KL-6 levels in a cluster analysis (G1, G2, G3, and G4). Both SP-A and KL-6 were elevated in the G1 group, with all the patients enrolled classified as progressive or unchanged, and 86.4% of patients showed improved disease activity in the G4 group, where both SP-A and KL-6 levels were reduced. In the G2 group, only SP-A levels decreased post-treatment, indicating an improvement in respiratory function; the patients were not at the end stage of the disease. Only the SP-A levels increased in the G3 group with immunosuppressive treatment.

Conclusions

Reduced serum SP-A and/or KL-6 levels are associated with improved lung function in patients with ILD. Some patients only showed a decrease in SP-A levels could prognosis an improvement in respiratory function. When only SP-A is increased, it may imply that the patients are at an early stage of disease progression. As a result, for proper disease monitoring, measuring both markers is important.

Serum KL-6 as predictive and prognostic marker of interstitial lung disease in childhood connective tissue diseases: a pilot study

This study was aimed to evaluate serum KL-6 levels to determine if this marker can be used for diagnosing and assessing severity of interstitial lung disease (ILD) in children with connective tissue disorders. In total, 40 patients [18 patients with juvenile systemic lupus erythematosus (JSLE), 10 patients with juvenile idiopathic arthritis (JIA), 8 patients with juvenile mixed connective tissue disease (JMCTD), 3 patients with juvenile systemic sclerosis (JSSc), and 1 patient with juvenile dermatomyositis (JDM)] and 20 healthy controls were included in this study. Age, sex, and duration of CTD and ILD (if any) were recorded. Blood samples from all the patients and controls were examined by ELISA. 20 of the 40 patients with CTD (50%) had ILD, 12 were mild and 8 were severe as assessed by spirometry. The median serum KL-6 level was 102.7 U/mL (76.1-180.8) in the CTD with severe ILD group, 72.2 U/mL (58.4- 100.5) in the CTD with mild ILD group, 56.7 U/mL (35.8-68.5) in the CTD without ILD group, and 52.3 U/mL (32.8-62.4) in the control group. KL-6 levels were significantly higher in the CTD with ILD (p<0.05), at a cutoff of 63.4 U/ml identified by ROC curve, serum KL-6 showed a sensitivity of 95.2% and specificity of 89.7%. KL-6 is a valuable biomarker for diagnostic purposes and to detect severity in ILD in childhood CTD.

Serum Krebs von den Lungen-6 for Predicting the Severity of COVID-19 Lung Injury: A Systematic Review and Meta-Analysis

Background

Lung injury is common in coronavirus disease 2019 (COVID-19) patients. The severity of lung injury appears to be reflected in serum Krebs von den Lungen-6 (KL-6), a glycoprotein expressed on type II alveolar epithelium. This study aims to assess the role of serum KL-6 in reflecting the severity of lung injury in COVID-19 patients.

Methods

A systematic search was conducted in Scopus, PubMed, Wiley Online Library, and ProQuest. Articles were screened based on several eligibility criteria and assessed for study quality using Newcastle-Ottawa Scale.

Results

This systematic review included four studies involving a total of 151 adult COVID-19 patients. Pooled analysis revealed that serum KL-6 was significantly higher in severe patients (SMD = 1.16; 95% CI = 0.69–1.63) with moderately high pooled sensitivity (79%; 95% CI = 61–91%) and specificity (86%; 95% CI = 72–95%).

Conclusion

High serum KL-6 may depict more severe lung injury in COVID-19 patients with moderately high sensitivity and specificity.

Krebs von den Lungen 6 (KL-6) as a marker for disease severity and persistent radiological abnormalities following COVID-19 infection at 12 weeks

INTRODUCTION

Acute presentations of COVID-19 infection vary, ranging from asymptomatic carriage through to severe clinical manifestations including acute respiratory distress syndrome (ARDS). Longer term sequelae of COVID-19 infection includes lung fibrosis in a proportion of patients. Krebs von den Lungen 6 (KL-6) is a mucin like glycoprotein that has been proposed as a marker of pulmonary epithelial cell injury. We sought to determine whether KL-6 was a marker of 1) the severity of acute COVID-19 infection, or 2) the persistence of symptoms/radiological abnormalities at medium term follow up.

METHODS

Prospective single centre observational study.

RESULTS

Convalescent KL-6 levels were available for 93 patients (male 63%, mean age 55.8 years) who attended an 12-week follow up appointment after being admitted to hospital with COVID-19. For 67 patients a baseline KL-6 result was available for comparison. There was no significant correlations between baseline KL-6 and the admission CXR severity score or clinical severity NEWS score. Furthermore, there was no significant difference in the baseline KL-6 level and an initial requirement for oxygen on admission or the severity of acute infection as measured at 28 days. There was no significant difference in the 12-week KL-6 level and the presence or absence of subjective breathlessness but patients with abnormal CT scans at 12 weeks had significantly higher convalescent KL-6 levels compared to the remainder of the cohort (median 1101 IU/ml vs 409 IU/ml).

CONCLUSIONS

The association between high KL-6 levels at 12 weeks and persisting CT abnormalities (GGO/fibrosis), is a finding that requires further exploration. Whether KL-6 may help differentiate those patients with persisting dyspnoea due to complications rather than deconditioning or dysfunctional breathing alone, is an important future research question.

Krebs von den Lungen-6 and surfactant protein-A in interstitial pneumonia with autoimmune features

Interstitial pneumonia with autoimmune features (IPAF) is a special subtype of interstitial lung disease that has received worldwide attention. Krebs von den Lungen-6 (KL-6) and surfactant protein-A (SP-A) can be used as an important biomarker of interstitial lung disease, but its exact relationship with IPAF is poorly understood.A total of 65 IPAF patients were included in the study and were followed up for 52 weeks. The KL-6 and SP-A were evaluated by chemiluminescence enzyme immunoassay. The above indicators were tested at 2 time points, baseline (the first admission of patients) and 52 weeks. We also collected the indicators of antinuclear antibodies and rheumatoid factor. Based on high-resolution computed tomography evaluations, patients were divided into: aggravation, stable, and improvement group. At same time, 30 age-matched normal people as normal control were recruited, the same information was collected. Correlations among the groups were compared and analyzed.The KL-6 and SP-A level in IPAF patients were significantly higher than normal controls (fold increase = 11.35 and 1.39, both P < .001) and differed significantly at baseline and 52 weeks in IPAF (difference ratio = 37.7% and 21.3%, P < .05, both). There were significant differences at baseline and 52 weeks (r values of aggravation, improvement, and stable groups for KL-6 were 0.705, 0.770, and 0.344, P = .001, .001, and .163, and for SP-A the r value were 0.672, 0.375, and 0.316, P = .001, .126, and .152). In aggravation group, KL-6 and SP-A were correlated with CT scores (both P < .05). Diffusing capacity of the lung for carbon monoxide (DLCO) and forced vital capacity (FVC), % predicted showed a progressive downward trend, with a significant difference at baseline and 52 weeks in IPAF patients (difference ratio = 23.8% and 20.6%, both P < .05). There was a significant correlation between KL-6 and FVC % predicted and DLCO (both P < .05), SP-A showed negatively correlated with DLCO, but not significantly correlated with FVC % predicted (P < .05 and .47).This study demonstrated that KL-6 and SP-A can reflect disease progression, and both 2 play a key role at reflection of lung epithelial cell injury and fibrosis degree in IPAF.

Proteomic characteristics of bronchoalveolar lavage fluid in critical COVID-19 patients

Up to 10-20% of patients with coronavirus disease 2019 (COVID-19) develop a severe pulmonary disease due to immune dysfunction and cytokine dysregulation. However, the extracellular proteomic characteristics in respiratory tract of these critical COVID-19 patients still remain to be investigated. In the present study, we performed a quantitative proteomic analysis of the bronchoalveolar lavage fluid (BALF) from patients with critical COVID-19 and from non-COVID-19 controls. Our study identified 358 differentially expressed BALF proteins (P < 0.05), among which 41 were significantly changed after using the Benjamini-Hochberg correction (q < 0.05). The up-regulated signaling was found to be mainly involved in inflammatory signaling and response to oxidative stress. A series of increased extracellular factors including Tenascin-C (TNC), Mucin-1 (KL-6 or MUC1), Lipocalin-2 (LCN2), periostin (POSTN), Chitinase 3-like 1 (CHI3L1 or YKL40), and S100A12, and the antigens including lymphocyte antigen 6D/E48 antigen (LY6D), CD9 antigen, CD177 antigen, and prostate stem cell antigen (PSCA) were identified, among which the proinflammatory factors TNC and KL-6 were further validated in serum of another thirty-nine COVID-19 patients and healthy controls, showing high potentials of being biomarkers or therapeutic candidates for COVID-19. This BALF proteome associated with COVID-19 would also be a valuable resource for researches on anti-inflammatory medication and understanding the molecular mechanisms of host response. DATABASE: Proteomic raw data are available in ProteomeXchange (http://proteomecentral.proteomexchange.org) under the accession number PXD022085, and in iProX (www.iprox.org) under the accession number IPX0002429000.

Diagnostic and prognostic predictive values of circulating KL-6 for interstitial lung disease: A PRISMA-compliant systematic review and meta-analysis

BACKGROUND

Past investigations showed inconsistent results for diagnostic and prognostic predictive values of Krebs von den Lungen-6 (KL-6) for interstitial lung disease (ILD).

METHODS

Web of Science and PubMed were systematically searched on for articles exploring the association of KL-6 and ILDs published between September 1993 and March 2019. For comparisons between-groups, the standard mean difference and 95% confidence intervals (CIs) were computed as the effect sizes. For diagnostic studies, a summary of sensitivity, specificity, positive likelihood ratios, negative likelihood ratios, and diagnostic odds ratio, which indicated the accuracy of KL-6 in the differentiation of ILDs and no ILDs, were calculated from the true positive, true negative, false positive, and false negative of each study. In addition, the summary receive-operating characteristics curve was constructed to summarize the TP and FP rates. For follow-up study, we computed hazard ratios (HRs) and 95% CIs for mortality. ILD patients showed elevated concentrations of KL-6, compared to healthy controls and patients without ILD.

RESULTS

The meta-analysis showed a sensitivity (0.85 [95% CI: 0.77-0.91]) and specificity (0.97 [95% CI: 0.90-0.99]) of KL-6 for ILDs. In addition, it showed elevated baseline circulating levels of KL-6 in subsequent active ILD, compared to subsequent inactive ILD. Moreover, there was a significant association between baseline levels of circulating KL-6 and mortality of ILD (HR 2.95, 95% CI 2.45-3.55, I = 65.9%, P = .032).

CONCLUSION

In conclusion, the study suggested that circulating KL-6 showed diagnostic and prognostic predictive values for ILDs.

Evaluation of the Diagnostic Efficacies of Serological Markers KL-6, SP-A, SP-D, CCL2, and CXCL13 in Idiopathic Interstitial Pneumonia

<b><i>Background:</i></b> The objective of this study was to evaluate the diagnostic value of serological markers Krebs von den Lungen-6 (KL-6), surfactant protein-A (SP-A), SP-D, chemokine ligand 2 (CCL2), and chemokine 13 (CXCL13) in idiopathic interstitial pneumonia (IIP). <b><i>Methods:</i></b> Patients with IIP aged 18–80 years from the First Affiliated Hospital of Guangzhou Medical University were enrolled in this retrospective case-control study. Data on the general patient characteristics, laboratory test results, chest high-resolution CT, and pulmonary function test results were collected. The diagnosis of idiopathic pulmonary fibrosis (IPF) was based on the international practice guidelines for the diagnosis and treatment of IPF, a collaborative effort published by the American Thoracic Society (ATS)/European Respiratory Association (ERS), Japanese Respiratory Society, and Latin American Thoracic Society. The diagnostic criteria of non-IPF (N-IPF) followed the consensus classification of the IIPs, which was jointly issued by the ATS and ERS in 2002. The diagnosis of interstitial pneumonia with autoimmune features (IPAF) was based on the official research statement on IPAF, which was jointly issued by the ATS and ERS in 2015. Serum levels of KL-6, SP-A, SP-D, CCL2, and CXCL13 were measured. The differences in the expression of these biomarkers and their correlation with the severity of the disease were analyzed. The sensitivity, specificity, cutoff value, and area under the curve (AUC) value for each of the indices were determined using the receiver operating characteristic (ROC) curve analysis. <b><i>Findings:</i></b> Between September 2015 and October 2017, 69 patients with IIP. Of these patients, 19 had IPF, 23 had N-IPF, and 27 had IPAF. We also enrolled 20 age- and gender-matched patients with pneumonia and 15 uninfected individuals as normal control. The serum levels of KL-6, SP-A, ­SP-D, CCL2, and CXCL13 were significantly higher in patients with IIP than in patients with pneumonia and the normal controls. The detection of these markers was found to have better diagnostic efficacy in patients with IIP than in those with pneumonia. Of these markers above, KL-6 had the highest diagnostic value (AUC 0.96, 95% CI 0.93–0.99). Based on a logistics regression analysis, the combination of KL-6, CCL2, and CXCL13 had an improved diagnostic efficacy for IIP. In patients with IIP, the serum levels of KL-6, SP-A, CCL2, and CXCL13 all showed a significant negative correlation with the diffusing capacity of the lungs for carbon monoxide (DLCO; <i>r</i> = –0.36, –0.37, –0.36, –0.30, respectively; all <i>p</i> &#x3c; 0.05). Although their expression levels along with that of SP-D were elevated in patients with IPF, N-IPF, and IPAF, it was difficult to distinguish between these 3 conditions by detecting the 5 serum biomarkers together. Our findings indicate that the serum levels of KL-6, SP-A, SP-D, CCL2, and CXCL13 are notably elevated in patients with IIP and show significant correlation with the severity of interstitial lung lesions. Additionally, we further explore the diagnostic efficacy of 5 biomarkers in different types of IIP. It is the first time that the level of serum marker CXCL13 of N-IPF and IPAF patients was higher than IPF patients, which further enriched the study on serum markers for IIPs. Between September 2015 and October 2017, 69 patients with IIP. Of these patients, 19 had IPF, 23 had N-IPF, and 27 had IPAF. We also enrolled 20 age- and gender-matched patients with pneumonia and 15 uninfected individuals as normal control. The serum levels of KL-6, SP-A, SP-D, CCL2, and CXCL13 were significantly higher in patients with IIP than in patients with pneumonia and the normal controls. Of these markers above, KL-6 had the highest diagnostic value (AUC 0.96, 95% CI 0.93–0.99). Based on a logistics regression analysis, the combination of KL-6, CCL2, and CXCL13 had an improved diagnostic efficacy for IIP. In patients with IIP, the serum levels of KL-6, SP-A, CCL2, and CXCL13 all showed a significant negative correlation with the DLCO (<i>r</i> = –0.36, –0.37, –0.36, –0.30, respectively; all <i>p</i> &#x3c; 0.05). Our findings indicate that the serum levels of KL-6, ­SP-A, SP-D, CCL2, and CXCL13 are notably elevated in patients with IIP and show significant correlation with the severity of interstitial lung lesions. Additionally, we further explore the diagnostic efficacy of 5 biomarkers in different types of IIP. It is the first time that the level of serum marker CXCL13 of N-IPF and IPAF patients was higher than IPF patients, which further enrich the study on serum markers in IIPs. <b><i>Interpretation:</i></b> Although the combined detection of KL-6, CCL3, and CXCL13 significantly improves the diagnosis of IIP, detection of all the 5 markers together is unable to distinguish between IPF, N-IPF, and IPAF.