In patients hospitalized for severe COVID-19, the incidence of acute kidney injury (AKI) is approximately 40%. To predict and understand the implications of this complication, various blood and urine biomarkers have been proposed, including neutrophil gelatinase-associated lipocalin (NGAL), chemokine (C-C motif) ligand 14 (CCL14), cystatin C, leucine aminopeptidase (LAP), and soluble urokinase plasminogen activator (suPAR). This study, conducted between mid-January and early May 2021, aimed to assess the diagnostic and prognostic capabilities of these biomarkers in a cohort of COVID-19 patients monitored during the initial two weeks of hospitalization. Among the 116 patients included in this study, 48 developed AKI within the first three days of hospitalization (41%), with 29 requiring intensive care unit (ICU) admission, and the overall mortality rate was 18%. AKI patients exhibited a statistically significant increase in urinary LAP levels, indicating acute tubular injury as a potential mechanism underlying COVID-19-related renal damage. Conversely, urinary NGAL and CCL-14 excretion rates did not differ significantly between the AKI and non-AKI groups. Importantly, elevated plasma suPAR and cystatin C levels upon admission persisted throughout the first week of hospitalization and were associated with unfavorable outcomes, such as prolonged ICU stays and increased mortality, irrespective of AKI development. In conclusion, this study underscores the early predictive value of urinary LAP levels in identifying acute tubular injury in COVID-19-induced AKI. Moreover, elevated plasma suPAR and cystatin C levels serve as valuable prognostic markers, offering insights into the short-term morbidity and mortality risks among COVID-19 patients, regardless of AKI occurrence. These findings shed light on the complex interplay between COVID-19, renal injury, and biomarkers with diagnostic and prognostic potential.

Introduction: Uremic toxins have been shown to cause adverse pulmonary effects by inducing endothelial and epithelial dysfunction, disrupting the alveolar-capillary barrier, and increasing inflammation and oxidative stress. This article reviews these effects with a specific focus on chronic kidney disease and the mechanisms by which uremic toxins affect lung tissue. Methods: A narrative review was conducted using keywords related to uremic toxins and lung injury to search the PubMed database. An advanced literature review was conducted in PubMed to identify studies explaining the mechanisms underlying lung pathophysiology in chronic kidney disease (CKD), with particular focus on CKD-induced pulmonary epithelial and endothelial dysfunction. Additionally, to highlight the pathological processes of lung congestion in CKD, studies on CKD-induced dysfunction of the alveolar-capillary barrier were retrieved. Studies published up to November 2025 were evaluated. Results: A total of 148 articles were reviewed in full text. Uremic toxins negatively impact lung tissue structure and function through multiple mechanisms, including oxidative stress, inflammation, and direct effects. Uremic toxins appear to share signaling pathways in endothelial cells, including those linked to Mitogen-activated protein kinases (MAPK), the Aryl Hydrocarbon Receptor (AhR), the receptor for advanced glycation end products (RAGE), and pro-inflammatory transcription factors such as nuclear factor κB (NF-κB). Additionally, oxidative stress acts as a pro-inflammatory signal shared by several uremic toxins. The mechanisms behind the harmful interactions between CKD and lung disease are mostly unknown, although more evidence exists for acute kidney injury (AKI). Conclusions: Chronic kidney disease, which leads to the buildup of uremic toxins, negatively affects the lungs. Overall, the accumulation of uremic toxins in CKD impairs endothelial and epithelial cells and the alveolar capillary barrier. Further research is needed to understand the specific mechanisms underlying these effects and to identify therapeutic options to protect the lungs in these patients.

Pulmonary congestion (PC) is common in hemodialysis (HD) patients. We explored the association of anemia and pulmonary congestion in HD patients. A prospective pilot observational study included 18 patients on maintenance HD. Individual B-lines scores (BLS; 8-sites method) were obtained by lung ultrasound, before and after the first two consecutive HD sessions of the week (HD1-HD2), with different inter-dialytic intervals (68 vs. 44 h). Bioimpedance spectroscopy body composition (BIS) was performed before each HD session. Hemoglobin (Hb) levels, in addition to circulating markers of chronic inflammation (soluble urokinase Plasminogen Activator Receptor [suPAR], soluble Suppression of Tumorigenicity 2 [sST2]) were obtained. Mean (±SD) BLS values were quite elevated at all time points: Pre-HD1 (16 ± 5.53), post-HD1 (15.3 ± 6.63), pre-HD2 (16.3 ± 5.26) and post-HD2 (13.6 ± 5.83), respectively. No direct significant correlation was found between inflammation markers levels and BLS. However, mean levels (±SD, ng/mL) of suPAR pre-HD1 (7.88 ± 3.07) and pre-HD2 (7.78 ± 3.02) remained significantly above the normal range (<4 ng/mL), and sST2 levels reached 2-fold the upper normal value in most patients (27.4 ± 17.8). Pulmonary congestion reflected by BLS was negatively correlated to Hb levels pre-HD1 (R² = 0.439, p = 0.003), and pre-HD2 (R² = 0.301, p = 0.018). In addition, Hb levels were negatively correlated to global volume status estimated by BIS (R² = 0.351, p = 0.009). Hemoglobin levels were negatively correlated to pulmonary congestion and to the global volume status evaluated by BIS. Chronic inflammation markers were increased in HD patients, suggesting a complex volume- and non-volume-dependent pathophysiology of pulmonary congestion in HD patients.