key: cord-0931234-aidsz3st
authors: Zhao, Kang; Huang, Jucun; Dai, Dan; Feng, Yuwei; Liu, Liming; Nie, Shuke
title: Serum iron level as a potential predictor of COVID-19 severity and mortality: a retrospective study
date: 2020-06-21
journal: Open Forum Infect Dis
DOI: 10.1093/ofid/ofaa250
sha: eebbd25daa379dea3b0814874009d42856978208
doc_id: 931234
cord_uid: aidsz3st

BACKGROUND: Various types of pulmonary diseases are associated with iron deficiency. However, information on iron status in COVID-19 is scarce. METHODS: This study included 50 hospitalized patients with confirmed COVID-19. The role of serum iron in predicting severity and mortality of COVID-19 was evaluated. RESULTS: The most common symptoms of COVID-19 patients in this study were cough (82%), fever (64%), and chest distress (42%). Of the 50 patients, 45 (90%) patients had abnormally low serum iron levels (<7.8 μmol/L). The severity of COVID-19 was negatively correlated with serum iron levels before and after treatment and was positively correlated with C-reactive protein (CRP), serum amyloid A (SAA), D-dimer, lactate dehydrogenase (LDH), urea nitrogen, and myoglobin levels. Decreased serum iron level could predict the transition of COVID-19 from mild to severe and critical illness. 7 (53.8%) patients with lower serum iron level after treatment in the critical group had died. There was a significant difference in post-treatment serum iron levels between COVID-19 survivors and non-survivors . CONCLUSIONS: Serum iron deficiency was detected in the patients with COVID-19. The severity and mortality of the disease was closely correlated with serum iron levels. Low serum iron concentration was an independent risk factor for death in COVID-19 patients.

In December 2019, a novel coronavirus was identified among patients with pneumonia in Wuhan, Hubei Province, China, after which the virus rapidly spread worldwide 1 . As of June 7, 2020, there were 7047922 laboratory-confirmed cases worldwide, and 402827 deaths. A disease spectrum analysis of 44415 patients diagnosed with COVID-19 showed the case-fatality rate (CFR) of critically ill patients to be as high as 49% 2 .

In 2003, SARS caused 774 deaths in 29 countries and the CFR was about 10%. Thus, the mortality rate of COVID-19 critically ill patients was much higher than that of SARS 3 . It is, therefore, urgent to search for valuable and potential clinical laboratory parameters that can act as early warning indicators of the severity and mortality of COVID-19.

It has been shown that this emerging infection is caused by a new type of enveloped RNA coronavirus B, and thus it was named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 4 . Scientists have noted that SARS-CoV-2 enters the human body through angiotensin converting enzyme 2 (ACE2) receptors on the membrane of cells 5 . ACE2 receptors are found in type II alveolar epithelial cells of the human lungs, and thus the lungs became the main target of SARS-CoV-2 in COVID-19 6 . However, the specific pathogenesis of impaired lung function is still unclear. The iron uptake system has been demonstrated to be implicated in hospital-acquired pneumonia and chronic lung infections 7 . Lower body iron and high tissue iron levels have been associated with lower lung function and severe pulmonary inflammation, A c c e p t e d M a n u s c r i p t respectively 8 . Although the role of iron in COVID-19 is unknown, we hypothesized that lower serum iron levels would be associated with a greater risk of inflammation and a high severity and mortality of COVID-19. To test this hypothesis, we evaluated the level of serum iron before and after treatment and investigated the correlation between serum iron levels and the severity and mortality of the disease. 

Nasopharyngeal swab samples were collected for detection, and reverse transcription- (1) mild: with fever, respiratory or digestive symptoms, and physician-diagnosed pneumonia by chest computed tomography (CT); (2) severe: one of the following conditions: shortness of breath and respiratory rate ≥30 times/min, oxygen saturation ≤93% at rest, chest CT imaging showing lesion progression of more than 50% within 24-48 hours; (3) critical: meet any of the following rules: respiratory failure and need for mechanical ventilation, shock, and any other organ failure needing critical care and treatment.

Blood routine, serum iron before and after treatment, liver function, renal function, CRP, SAA, D-dimer, myocardial enzyme, brain natriuretic peptide, arterial blood gas analysis, creatine kinase, and lactate dehydrogenase were obtained. Data were analyzed by the research team of the third people's Hospital of Hubei Province. Exposure history, course of disease, clinical symptoms, laboratory tests, chest CT images and treatment data were obtained from medical records.

Categorical variables were described as frequency rates and percentages, and Multivariate logistic regression analysis was used to determine the independent risk factors for death in COVID-19 patients. All statistical analyses were performed using SPSS 26 software. A P value less than 0.05 was considered statistically significant.

This study included 50 hospitalized patients with confirmed COVID-19. The median age of the patients was 55 years (IQR 44-66) and 20 (40%) were women. All patients were residents of Wuhan and had been in contact with patients with COVID-19. Among the 50 patients included in our study, the most common symptoms at the onset of COVID-19 were cough (82%), fever (64% on admission), and chest distress (42%).

The second most common symptoms were fatigue (20%), sputum production (10%), anorexia (8%), diarrhea (4%), dyspnea (4%), and cardiovascular symptoms such as palpitations (4%) ( Table 1) .

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Lymphopenia was the main feature of patients with COVID-19, and lower lymphocyte counts were found in the critical group than in the mild group 

To investigate the possible role of serum iron in the pathogenesis of the disease, we analyzed the correlation between serum iron levels and other variables. We found that A c c e p t e d M a n u s c r i p t the severity of COVID-19 was negatively correlated with serum iron levels before and after treatment and was positively correlated with CRP, SAA, D-dimer, LDH, urea nitrogen, and myoglobin levels. A significant and negative correlation between severity of disease and serum iron levels before (r = -0.390, p＜0.001) and after treatment (r = -0.31, p = 0.034) was detected. There were also significant negative correlations between pre-treatment serum iron and other laboratory parameters, including CRP (r = -0.49, p＜0.001) and SAA (r = -0.37, p = 0.010) (Figure 1 ).

In order to evaluate the value of lymphocytes and serum iron in predicting the severity and mortality of COVID-19, a receiver-operating characteristics (ROC) curve and an area under ROC curve (AUROC) were performed. A decrease in lymphocyte count, percentage of lymphocytes, and serum iron levels before treatment were of great value in predicting the transition of COVID-19 from mild to severe and critical illness ( Figure   2A ). AUROC and 95% confidence interval (95% CI) of lymphocyte count, percentage of lymphocytes, and pre-treatment serum iron were 0.913 (95% CI 0.827-1.000), 0.952(95% CI 0.895-1.000) and 0.696 (95% CI 0.548-0.844), respectively. The cutoff value of lymphocyte count and percentage were 0.83×10 9 /L (sensitivity: 93.5%; specificity: 84.2%) and 13.15% (sensitivity: 90.3%; specificity: 94.7%). The cutoff values of serum iron before treatment were 5.26 μmol/L (sensitivity: 58.1%; specificity: 89.5%). Lymphocyte count, percentage of lymphocytes, and serum iron levels after treatment could be used to predict the mortality of COVID-19( Figure 2B) . AUROC A c c e p t e d M a n u s c r i p t and 95% CI of lymphocyte count, percentage of lymphocytes, and post-treatment serum iron were 0.971 (95% CI 0.927-1.000), 0.887 (95% CI 0.785-0.988) and 0.929 (95% CI 0.844-1.000), respectively. The cutoff values for lymphocyte count and percentage were 0.435×10 9 /L (sensitivity: 100%; specificity: 91.1%) and 5.65% (sensitivity: 100%; specificity: 77.8%). The cutoff value for serum iron before treatment was 12.54 μmol/L (sensitivity: 100%; specificity: 77.8%). The ROC curve is shown in Figure 2B .

Multivariate logistic regression analysis was used to determine whether the age, lymphocyte%, lymphocyte count, pre-treatment serum iron level, and post-treatment serum iron level were the independent risk factors for death in patients with COVID-19. Death of the COVID-19 patients was set as the dependent variable, mutlivariate analyses showed that old age and low post-treatment serum iron level were the independent risk factors for the death in COVID-19 patients (p=0.013 vs p=0.006).

All patients in this study were administered with supportive treatments. All 50 (100%) patients received antiviral therapy (oseltamivir or arbidol), 36 (72%) received antibiotic therapy, 44 (88%) received immunomodulatory therapy (hydroxychloroquine or chloroquine phosphate), and 34 (68%) were given short-term (3-5 days) and low-dose systematic corticosteroids; higher percentages of severe patients received these therapies (Table 4) . Severe and critical patients had a higher percentage of antibiotic A c c e p t e d M a n u s c r i p t therapy and corticosteroid use than those in the mild group (p < 0.001). As of March 12, 2020, the final date of follow up, 42 of 50 patients (84%) had been discharged, 1 (2%) was under hospitalization, and 7 (14%) had died. Critical patients with COVID-19 had a higher percentage of hospitalization (7.7% vs. 0%) and mortality (53.8% vs. 0%) than those with mild disease (Table 4 ). Chest CT images showed multiple small patches and interstitial changes in the lungs after the onset of symptoms (Figure 3 ). Absorption of bilateral ground-glass lesions was found with increased level of post-treatment serum iron in all groups except for the critical group (Figure 3 A, B & C) . Patients in the critical group who died had more severe chest CT images, including multiple lobular and subsegmental areas of consolidation ( Figure 3D ).

We firstly reported an iron deficiency in COVID-19 patients. We then reported a close correlation between low serum iron and high severity of the disease. A total of 45 of 50 (90%) patients had abnormally low serum iron levels (<7.8 μmol/L) in this study.

Various types of pulmonary diseases have been associated with iron deficiency. A lack of iron resulted in allergic asthma, while iron supplementation could decrease chronic cough hyperresponsiveness and allergic inflammation in the lungs 8, 9 . Iron deficiency was highly prevalent in idiopathic pulmonary arterial hypertension, and the extent of iron deficiency was also related to hemodynamics 10 . The level of serum iron was thought to be an independent predictor of in-hospital mortality in critically ill patients 11 . We noted that patients with COVID-19 who died during hospitalization had markedly severe chest CT images and significantly lower serum iron levels compared A c c e p t e d M a n u s c r i p t with those who survived before and after treatment.

Combination of a variety of chronic diseases was one of the factors that contributed to the high mortality of critically ill patients with COVID-19. In our study, coexisting disorders in severe patients with COVID-19 included hypertension (34%), cardiovascular disease (12%) and diabetes (12%). A higher percentage of comorbidities (hypertension (41.2%) and diabetes (30.8%)) was found in critical patients than in mild and severe patients, and with a greater mortality in the severe group than in the other two groups (53.8% vs. 0%). The most common symptoms at the onset of illness were cough (82%), fever (64% on admission), and chest distress (42%), which is consistent with a previous study. However, the percentage of patients with a cough was higher in our study (82% vs. 67.8%) 12 . Serum iron was found to be closely correlated with chronic cough 9, 13, 14 . Previous research showed that non-smoking women with chronic unexplained cough should be checked for iron deficiency and iron supplementation may resolve this symptom 9 . It was intriguing that oral intake of iron attenuated angiotensin converting enzyme inhibitor therapy related cough through its effect on NO generation 13 .These results suggest that iron deficiency might be one of reasons why cough symptoms accounted for a major percentage of the symptoms in COVID-19 patients. We also noted that 44 (88%) patients in our study received non-iron anti-cough therapy, indicating that oral of iron supplements can be used as an alternative treatment for cough in COVID-19 patients.

CRP and SAA were acute phase reactants associated with an overactive inflammatory response. CRP was associated with 28-day mortality and had prognostic significance M a n u s c r i p t in hospitalized patients with community-acquired pneumonia 15 . In this study, D-dimer, fibrinogen, CRP, SAA, and LDH levels were significantly increased in critically ill patients than in mild and severe patients, which is consistent with a previous study 12 .

Four (30.8%) patients in the critical group showed abnormally increased TNI levels.

Patients in the critical group had higher BNP and myohemoglobin levels than those in the mild and severe groups, suggesting the cardiovascular system is implicated in the progression of COVID-19. The specific role of the cardiovascular system in the pathogenesis of this emerging infectious disease is still unclear. The high expression of ACE2 in the endothelial cells of coronary arteries and the immune damage caused by cytokines released by inflammatory storms in critically ill patients might explain why the cardiovascular system is affected 16, 17 . After analyzing the correlation between severity of disease and laboratory indexes, we found that the severity of COVID-19 was negatively correlated with serum iron levels before and after treatment. Further ROC analysis demonstrated that post-treatment serum iron level could predict the mortality of the illness. However, serum iron levels before treatment did not have a role in predicting the mortality of COVID-19.

As a retrospective study, this study has some notable limitations. First, it was only performed in a single center, and only 50 subjects were enrolled in this study. Thus, the results of our study need to be confirmed in a large population study. Second, because data generation was clinically driven and not systematic, we did not include other iron metabolism markers such as serum ferritin and transferrin. Third, most patients did not undergo sputum pathogenic bacteriologic or fungal detection during hospitalization due A c c e p t e d M a n u s c r i p t to overwhelmed medical resources.

In conclusion, we demonstrated that serum iron deficiency was one of the features in the patients with COVID-19. The severity and mortality of the disease was closely correlated with serum iron levels. Low serum iron concentration after treatment was an independent risk factor for death in COVID-19 patients.

M a n u s c r i p t The severity of COVID-19 was negatively correlated with serum iron levels before and after treatment and was positively correlated with CRP, SAA, D-dimer, LDH, urea nitrogen, and myoglobin levels. Pre-treatment serum iron levels were negatively correlated with CRP and SAA levels. A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t 

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No funding needs to be declared.

KZ and S-KN conceptualized the paper. S-KN analyzed the data, with input from KZ, J-CH and Y-WF. S-KN and L-ML wrote the initial draft with all authors providing critical feedback and edits to subsequent revisions. All authors approved the final draft of the manuscript.

The authors have no conflicts of interests to declare. There are no relationships or activities that could appear to have influenced the submitted work. This study has never been previously presented in any meetings.

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