Disclaimer: The aim of these rapid reviews is to retrieve, appraise, summarize and update the available evidence on COVID-related health technology. The reviews have not been externally peer- reviewed; they should not replace individual clinical judgement and the sources cited should be checked. The views expressed represent the views of the authors and not necessarily those of their host institutions. The views are not a substitute for professional medical advice.

Copyright Claims: This review is an intellectual property of the authors and of the Institute of Clinical Epidemiology, National Institutes of Health-UP Manila and Asia-Pacific Center for Evidence Based Healthcare Inc.

BACKGROUND

Since the outbreak of the COVID-19 pandemic, it has been observed that around 20% of infected persons develop moderate to critical illness that can lead to fatal complications.1 More than 40,000 deaths have been reported globally, with a crude mortality rate of 3 to 4%.2,3 While reported to be less fatal than the Severe Acute Respiratory Syndrome coronavirus (SARS-CoV) and Middle East Respiratory Syndrome coronavirus (MERS-CoV) infections, COVID-19 is highly contagious and can cause immediate

deterioration; hence, there is a crucial need to recognize cases with imminent danger of mortality needing urgent medical attention.4

To meet this need, several studies have investigated laboratory tests that may reflect the processes involved in the clinical deterioration of infected patients. These three main processes are as follows: 1) sustained viremia and systemic inflammatory response resulting in multiple organ damage; 2) immune dysregulation and cytokine storm; and 3) dysfunction of the renin-angiotensin system, increased pulmonary vascular permeability, and subsequent pulmonary edema leading to acute respiratory distress syndrome and death.1 All of these occur following the entry of the virus into the cell and its binding to the human angiotensin-converting enzyme 2 (ACE2), which is expressed in lung, heart, kidney, and intestinal tissues.5,6

This review summarizes the available evidence on laboratory biomarkers as prognostic factors in COVID-19.

METHODS

See General Methods Section.

Articles were selected based on the following inclusion criteria:

•Population: COVID-19 patients aged 18 years and above, excluding pregnant patients

•Exposure: Laboratory markers, any type

•Outcomes: Severe COVID-19, critical COVID-19, or death

•Study designs: systematic reviews and meta-analyses, observational studies (prospective or retrospective cohort studies) with adjustments for confounding factors

RESULTS

Characteristics of Included Studies

As of April 1, 2020, we found 17 articles that fulfilled our inclusion criteria. One was a meta-analysis7 and the rest were retrospective cohorts published in February or March of this year. One cohort study was from Japan8 and the rest were from China. The sample size of the cohort studies ranged from 78 to 701. The systematic review and meta-analysis included 6 studies that enrolled 1302 patients.

One additional study found on April 12, 2020 did not fulfill the inclusion criteria because there was no control of confounders done. However, it was included because it reported the onset of significant differences in values of three laboratory parameters that were found by other studies to be important.9

The cohorts included hospitalized adults with mild to critical COVID-19. Most studies included demographic and clinical characteristics and laboratory results in their analysis. The outcome of interest was death in eight studies9–16, identification of severe or critical disease on admission in

four 8,17–19, disease progression in four16,20–22 or a composite of death or disease progression in two.23,24 (See Appendix 1,

Characteristics of Included Studies)

Critical Appraisal

Guide questions from the book Painless Evidence- Based Medicine were used for the critical appraisal of included studies.25 Elements of the studies that were found to be of high or unclear risk of bias include the following: objective definition of outcome (admission to the intensive care unit)22; incomplete follow-up wherein some patients have not yet developed the outcomes under study on the date of assessment (short interval between admission and date of assessment of outcome)16,21–24; and the lack of validation studies for a competing risks survival model.21

Studies included both adult male and female patients of Asian race, as well as information on their comorbidities. Most studies, which were conducted in hospitals across China, included patients who were symptomatic and required hospital admission; this entails an inherent bias in patient recruitment, with moderate to critical disease having a larger representation among the study populations. Nonetheless, this is also the population to which the results of prognostic studies shall be applied. In terms of applicability, the availability, cost, and turnaround time of laboratory tests may present an issue. Certain tests such as IL-6 and procalcitonin may be accessible only within the National Capital Region and some large cities of the country.

Most of the included studies reported the odds ratios or hazard ratios of the outcomes of interest, and these were found to cause statistically significant risk or harm.

Overall, the studies appraised were found to be valid, and the results can give us some guidance in identifying persons at higher risk of clinical deterioration based on their laboratory findings in addition to other risk factors of age, smoking, and comorbidities. (See Appendix 2,

Critical Appraisal of Included Studies)

Prognostic Outcomes

Death (7 studies)

Two studies (Xie et al. and Yan et al) proposed models for prediction of death among hospitalized patients. Xie et al. presented a nomogram wherein lymphopenia, high LDH, and low level of oxygen saturation were poor prognostic indicators.10 In Yan’s model, LDH, lymphocyte count, and hs-CRP beyond cut-off values, taken at any time point during the hospitalization, can predict poor outcome.11

Taken individually, the different laboratory findings associated with increased risk of death are the following:

•High LDH: The likelihood of in-hospital death is higher with high LDH levels. One study reported a HR of 1.30 (1.11, 1.52). Two studies reported LDH cut-off values of >225 U/L [OR 1.010 (1.005, 1.015)]14 and 365 U/L (no HR or RR reported).11

•High D-dimer: This was associated with higher odds of in-hospital death at a cut-off value of > 1 ug/L [OR 18.42 (2.64,128.55)].15 In another study for which no cut-off values were reported, HR of death was at 1.02 (1.01, 1.04).16

•High BUN and serum creatinine: A study reporting on kidney injury markers showed that the risk of death was higher with high levels of baseline BUN [HR 4.20 (2.74, 6.45)], serum creatinine [HR 2.04 (1.32, 3.15)], and a peak serum creatinine value of > 133 umol/L [HR 3.09 (1.95, 4.87)].12

•High markers of kidney injury (other): Risk of death was increased with proteinuria of any degree, especially when dipstick value was at 2+ to 3+ [HR 6.80 (2.97, 15.56)].The same association was made between death and hematuria of 2+ to 3+ dipstick values [HR 8.89 (4.41, 17.94)].12

•High hs-TnI: Risk of death was significantly higher in patients with hs-TnI levels >99th percentile of the upper reference range during time from symptom onset [HR 4.26 (1.92, 9.49)] or time from admission [HR 3.41 (1.62, 7.16)] to study end point.13

Severe disease on admission (4 studies)

•Lymphopenia: This was found to be significantly higher in severe cases [adjusted OR, 4.30 (1.50, 3.75)].8 Low lymphocyte count expressed as high baseline neutrophil lymphocyte ratio [OR 1.6 (1.04, 1.53)].19

•High serum creatinine: Similar to OR 1.03 (95% CI 1.0-1.05).17

•Chest CT scan findings: Consolidation was associated with a higher risk of severe disease on admission if consolidation was detected [adjusted OR 3.24 (1.04, 10.40)].8 Higher total radiograph score or CT severity score (including ground-glass opacities, consolidation, crazy paving, etc.) also lead to a higher risk of severity as reported by two different studies. [OR ranging from 1.25 (1.08,1.46) to 6.28 (3.9, 10.1)].17,19

•Other markers for increased risk of severe disease on admission were high BUN, high direct bilirubin, high red cell distribution width (RDW), and low albumin but odds ratios were not reported.18

Disease progression (4 studies)

•The following markers were associated with the development of acute respiratory distress syndrome (ARDS):16

Neutrophilia [HR, 1.14 (1.09, 1.19]

High LDH [HR, 1.61 (1.44-1.79)]

High D-dimer [HR, 1.03 (1.01, 1.04)

High IL-6 levels Ratio of Means 2.9 (1.17, 7.19)7

•High CRP (>10mg/liter) was associated with progression to severe COVID-19 but odds ratio was not reported.20

•One study reported reduced risk of intensive care unit (ICU) admission per 100 cell/ul increase in CD4+ T cell count.22

Composite death or progression (2 studies)

•Greater risk of death or disease progression was associated with the following: 24

albumin [OR 7.353 (1.098, 50.000)]

CRP [OR 10.53 (1.224, 34.701)]

•Other markers for this composite were hypersensitive troponin I (>0.04 pg/mL), leukocytosis (>10 x 109/L), and neutrophilia (>75 x 109/L) 23

The study of Tan et al showed that those who died or had severe or critical disease compared with those who were cured or had moderate disease had an early significant decrease in % lymphocytes on day 1 to 2 of hospitalization and a significant increase in levels of IL-6 and CRP on day 2 to 4. These changes were consistent throughout the patients’ clinical course. Although this study did not control for confounders, its report of the time of first occurrence of a significant difference in the values of the tests of interest (% lymphocytes, CRP, IL-6) is quite unique and may by itself be clinically significant.9

IL-6 is a known biomarker for cytokine storm, which is implicated as one of the causes of clinical deterioration in COVID-19.1 A systematic review and meta-analysis on interleukin-6 in COVID-19 showed elevations in IL-6 levels in all six studies. Compared to patients with non- complicated disease, IL-6 levels in those with complicated COVID-19 were 2.9-fold higher. However, in the meta- analysis, there was significant heterogeneity among the studies, and this persisted despite sensitivity analysis.7

The study by Qin, included in the systematic review, identified that severe cases also have significantly elevated levels of other serum inflammatory biomarkers compared with non-severe cases, including IL-2R (757 U/mL versus

663.5U/mL; p=0.001), ferritin (800.4 mcg/L versus 523.7 mcg/L; p p<0.001), TNF-α (8.7 pg/mL versus 8.4 pg/mL; p=0.037), IL-10 (6.6 pg/mL versus 5.0 pg/mL;<0.001) and CRP (57.9 mg/L versus 33.2 mg/L; p<0.001).26 Ferritin, which is a commonly used test for cytokine storm, did not appear as a significant risk factor in all other studies we reviewed.

In clinical practice, the use of scoring systems including the above tests may facilitate the determination of an over-all assessment of prognosis. However, these will need to be validated prior to use.

Recommendations from Other Guidelines

Lymphopenia, neutrophilia, high ALT and AST, high LDH, high CRP, high ferritin, and high D-dimer were mentioned in the interim management guideline by the Centers for Disease Control and Prevention as tests that may be associated with greater disease severity and mortality, but no specific recommendations were made as to the collection, measurement, and use of these markers in the overall prognostication of COVID-19 patients.27 Similarly, no such particular recommendations were found in existing

interim guidelines from the World Health Organization and from China.

CONCLUSION

Several laboratory tests were found to be associated with severe COVID-19, and these may be used to prognosticate and guide management. Limitations of current available evidence include small sample sizes, the absence of laboratory cut-off points for reference and inclusion of only severe cases in some studies, and the lack of validation of some proposed predictive models.

Declaration of Conflict of Interest

No conflict of interest.

References

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2.WHO. Q&A: Similarities and differences – COVID-19 and influenza. 2020;1–4. Available from https://www.who.int/news-room/q-a-detail/ q-a-similarities-and-differences-covid-19-and-influenza

3.WHO. #Covid19 Coronavirus Disease 2019: Situational Report 72. DroneEmprit [Internet]. 2020;2019(April):1–19. Available from https://pers.droneemprit.id/covid19/

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Comparisons between complicated and non- complicated groups

Patients requiring ICU admission versus not requiring

Severe or critical COVID-19 versus mild Complicated defined as needing hospitalization, ICU admission, ARDS, invasive mechanical ventilation, renal replacement therapy and severe disease on clinical scoring tools, or death

Ratio of means 2.9 (1.17, 7.19)

Mean IL-6 is 2.9 fold higher in complicated COVID-19 compared to non-complicated disease.

Severe symptomatic cases: with symptoms of pneumonia (dyspnea, tachypnea, SpO2) <93%, needing oxygen therapy

28 patients in severe group

Consolidation detected by chest CT scan (adjusted OR: 3.24; 95% CI; 1.04-10.40; p = 0.04), and lymphopenia (adjusted OR, 4.30; 95% CI; 1.50-13.75; p < 0.01) were found to be significantly higher in severe cases

Unfavorable outcome (disease progression, death, or non-improvement of severe or critical status)

Unfavorable outcome in 63 patients (19.5%)

Age over 65 years, smoking, critical disease status, diabetes, high hypersensitive troponin I (TnI) (>0.04 pg/mL), leukocytosis (>10 x 109/L) and neutrophilia (>75 x 109/L) predicted unfavorable clinical outcomes.