This study proposes an easy-to-use panel of five clinical and laboratory parameters to aid in the prediction of disease progression in COVID-19 patients. The model including age > 65 years, male sex, cardiovascular disease, dyspnoea and at least three abnormal blood parameters among CRP (> 80 U/L), ALT (> 40 U/L), NLR (> 4.5), LDH (> 250 U/L), and CK (> 80 U/L) shows fair discrimination ability (AUC 0.73). To our knowledge, this is the first study assessing predictors of disease progression at specific time-points starting from the onset of COVID-19 symptoms.
Since the start of the pandemic, a wide range of predictive models and scores has been published with the common goal of informing clinical decision making and optimising resource allocation. An observational cohort of 1157 patients acutely admitted to two London hospitals analysed several demographics, clinical, laboratory and imaging factors likely to predict mortality, highlighting a correlation of male sex, older age, hypertension, chronic lung diseases and higher levels of lymphocytes, CRP and creatinine, among the others, with critical care admission and/or death7. A systematic review of ten prognostic models revealed that the most reported predictors of disease progression and mortality were age, sex, CRP, LDH and lymphocyte count.9 Recently, the predictive value of NLR measured at hospital admission has been assessed in a prospective cohort, showing a high value in predicting disease deterioration, shock and death (all the areas under the curve > 0.80).13 The vast majority of these models assessed the predictors by considering the hospital admission as baseline time-point, 10–13 and share therefore the common drawback of including patients at varying stages of the disease.
In our cohort, more than one-third (37%) of patients experienced disease progression by day-11 of symptoms onset. Descriptive studies on clinical course of COVID-19 revealed that the median time from onset of illness to acute respiratory distress syndrome and to ICU admission was 8–12 days and 9.5–12 days, respectively.14 These findings would seem to indicate that clinical deterioration with the need of higher level of care may occur at a very early stage of the disease and suggest that setting “onset of symptoms” as baseline time-point leads to inclusion of patients with homogeneous disease length.
Older age and the presence of cardiovascular comorbidities were associated with a higher risk of unfavourable outcome, as highlighted by other studies.7,15,16 Comorbidities, secondary bacterial infections, and altered cellular and humoral immune functions are more common in the elderly, thus increasing the risk of developing severe illness. A meta-analysis of 51 studies including a total of over 48,000 patients with confirmed COVID-19 infection showed that fatal outcomes with COVID-19 infection were strongly associated with diabetes, hypertension and cardiovascular diseases across all age groups, thus suggesting that the risk of poor outcome associated with cardiovascular diseases may be not affected by age.17 In the present cohort, no statistically significant differences between male and female were observed with regards to the outcome, while in most of the studies the severity and mortality of COVID-19 have been reported to be higher in males than in females. Sex-related differences in immune system responses to pathogens has been observed, with female eliciting higher immune responses. Furthermore, RNA clearance has been reported to be delayed in male patients with COVID-19.18
Laboratory assessment on day-5 of symptoms onset showed several parameters with significant mean differences between patients with or without poor outcome. In particular, poor outcome was associated with higher NLR, CRP, LDH, and CK, according with several studies.12,19 Lymphopenia and elevated neutrophil count suggest an alteration of lymphocyte function and are associated with elevated secretion of IL-6 and TNF-alpha, contributing to generalized inflammation. This inflammatory state, when persistent and uncontrolled, may lead to acute respiratory distress syndrome and rapid deterioration of the clinical conditions. IL-6 upregulates hepatic CRP production, thus suggesting the plausibility of the clinical use of this inflammatory biomarker as a prognosis predictor for COVID-19 patients.9 Similarly, LDH blood level increases in case of cell damage and is a marker of various inflammatory states. A systematic review and meta-analysis of 28 studies reporting LDH levels in severe vs. non-sever COVID-19 patients confirmed that LDH level can be used as a COVID-19 severity marker and is a predictor of survival20 CK, a marker of muscle damage, has been associated with a more severe COVID-19. Currently, it remains unclear whether increased levels of CK in COVID-19 patients is due to a virus-triggered inflammatory response or direct muscle toxicity.21 Elevation of liver transaminases during SARS-CoV-2 infection has been frequently reported. Possible pathophysiology mechanisms include direct effect of the virus, liver injury mediated by uncontrolled immune response drug toxicity and ischemic hepatitis due to multiorgan dysfunction.22 Based on these evidences and on our findings, patients affected by COVID-19 may benefit from blood testing including inflammation markers, complete blood count and transaminases within the first week after symptoms onset to evaluate the risk of developing a life-threatening disease.
In a recent work, a large group of Italian experts was invited to complete an online survey through the PAPRIKA (Potentially All Pairwise RanKings of all possible Alternatives) method 23 with the aim of determining the weights of several criteria for prioritizing COVID-19 patients for hospitalization.24 Among a list of criteria, including age, body mass index, comorbidities, findings at chest X-ray, CRP, and duration of symptoms among others, the highest weights were attributed to PaO2 and peripheral oxygen saturation, denoting the well-known central role of respiratory findings in the assessment of the risk of rapid deterioration of COVID-19 patients. These findings, alongside those outlined in our study, suggest that in addition to considering symptoms onset and duration, the typology of symptoms should also be taken into account in an early risk assessment of COVID-19 deterioration.
This study has several limitations. First, the sample size limits the accuracy of the findings. Second, the study was performed in a single centre, hampering the generalizability and the applicability of the results to other settings. Third, the model did not undergo external validation and might be at risk of overfitting. However, we tried to mitigate overfitting by decreasing the number of predictors. The results from this study highlight the importance of relying on homogeneous populations with same length of disease in order to build the best possible prediction model for disease progression in COVID-19 patients and allow optimal treatment and resource allocation.
This study shows how an easy-to-use panel of five laboratory and clinical parameters applied in patients with COVID-19 at day-5 of symptoms onset can predict disease progression with fair discriminatory power. It further suggests that the onset of symptoms might represent a useful and reliable baseline time-point for developing prognostic models. The assessment of few variables at the right time may contribute to early identification of patients at major risk of developing life-threatening COVID-19. The model can also play a role as a tool to increase homogeneity of population in clinical trials on COVID-19 treatment in hospitalized patients. A validation study is needed to evaluate whether this model can reliably inform decision making and identify proper level-of-care requirements for hospitalized patients.