Utility of Various Biomarkers in Management of COVID-19

The COVID-19 pandemic has sparked off mounting crisis in every sphere of our lives, and we are realizing that this unceasing outbreak is yet to beget profound consequences. WHO announced COVID-19 as a pandemic on March 11, 2020.1 The early strategy to mitigate this pandemic has been largely limited to reducing exposure through preventive measures like maintaining social distance, frequent hand washing, use of sanitizers, and wearing masks. At the country level, Nepal also imposed a nationwide lockdown on March 24, 2020, in an effort to reduce the spread of the virus.2 The second strategy has been to Identify and isolate cases through nucleic acid amplification test (NAAT), keeping confirmed cases in isolation centers and COVID-19 hospitals, with contact tracing and quarantine of the individuals exposed to the confirmed cases.

There are designated COVID hospitals and other hub and satellite hospitals spread throughout the country assigned for management of COVID-19 cases. Cases are being admitted to isolation wards and critical care units. Routine investigations are an integral part of COVID-19 management, required to understand progression of the disease. Such investigations include various biomarkers that play decisive roles in the management of COVID-19.This piece discusses the important biomarkers that are available in clinical laboratories, which have role in diagnosis, therapeutic management, and predicting severity and outcome of the disease.

Molecular testing: Nucleic Acid Amplification Test (NAAT)

WHO interim guideline for testing of SARS-CoV-2 recommends nucleic acid amplification test for screening and confirmation of COVID-19 disease.3 rRT-PCR remains the most commonly employed NAAT for diagnosis of COVID-19 worldwide.4 The genes targeted by rR-TPCR include nucleocapsid (N), envelope (E), spike (S), RNA dependent RNA polymerase (RdRp), and Open Reading Frame 1ab (ORF1ab).3,4 Since, COVID-19 is wide-spread in Nepal, laboratories involved in providing rRT-PCR test results can just make confirmatory diagnosis based on amplification of a single target area using authorized and validated assays.3

Ideally, the specimen required for the test may be obtained from the lower respiratory tract, such as sputum, aspirates, lavage, pleural fluid and lung biopsy, for patients presenting with severe disease, and from the upper respiratory tract, which includes nasopharyngeal swab/aspirate/wash or oropharyngeal swab for ambulatory patients.3,4 Of all these specimens, lower respiratory tract specimens are consistent with best viral loads and extended duration of viral shedding, compared to upper respiratory tract specimens.5

Viral load has been found to be higher in case of severe COVID-19 disease, compared to mild disease, and may thus prove to be a useful marker of disease severity and prognosis.6 Other than respiratory samples, there is evidence that SARS-C0V-2 virus is shed in stool for about 6-10 days, even after nasopharyngeal swabs turn negative, and thus, specimens could be potentially used where nasopharyngeal specimens fall behind in viral detection. Interestingly, some studies have reported negative SARS-CoV-2 in urine specimens.7,8

Complete Blood Count (CBC)

CBC is the most common routine investigation provided by the laboratory for various disease conditions. Lymphopenia and higher neutrophil to lymphocyte ratio has been reckoned as a marker of disease severity and prognosis, respectively.9,10

Inflammatory Biomarkers

C- reactive Protein (CRP) is an acute-phase protein released by the liver in response to Interleukin-6, and is a known marker of inflammation. Recent evidence suggests CRP as a useful marker for assessment of disease severity.11 In addition, CRP can predict disease severity in the early stages of COVID-19.12 It has also been deemed as a predictive marker of disease outcome.13

Alternatively, lymphocyte to CRP ratio has also been recognized as a marker that significantly decreases in COVID-19 patients, indicating degree of inflammation and need for invasive mechanical ventilation.14 Furthermore, in the monitoring of Tocilizumab therapy for Interleukin-6 (IL-6) induced cytokine storm, CRP has a decisive role.15 CRP is one of the established biomarkers in many laboratories of Nepal. The designated COVID hospitals and other hospitals in Nepal can use this marker as an indicator of disease severity, prognosis, and therapeutic management of patients with COVID-19.

Procalcitonin (PCT) is also a marker of inflammation and infection. PCT is elevated in bacterial infection and remains within reference range in viral infection, and hence, proves to be a useful marker to guide antibiotic therapy.16 COVID-19 disease, caused by SARS-CoV2, is a viral infection, and elevation of PCT after hospital admission is suggestive of bacterial co-infection.17 PCT has been found to be progressively increased in COVID-19 with disease severity, and therefore considered as an index of disease prognosis if measured serially.18

Interleukin-6(IL-6): Cytokine storm syndrome, or macrophage activation syndrome, has been postulated as the major driver of severe COVID-19 disease. The major cytokine expressed and elevated is IL-6.19 Tocilizumab is a monoclonal antibody known to block IL-6 receptor and is FDA approved for use in COVID-19 disease.20 Recent evidence suggest use of Tocilizumab in COVID-19 disease reduces the requirement of invasive ventilation.21 Additionally, it has been found to improve oxygen requirement and radiographic changes.22 Measurement of IL-6 level may be useful in administration and monitoring of Tocilizumab therapy.23 Furthermore, it also aids as an indicator of disease severity and prognosis.13

Ferritin: Hyperferritinemia is another consequence of COVID-19 disease. Ferritin is secreted by macrophage in lung tissue following SARS-CoV-2 infection and is also elaborated by cytokines. Severe form of COVID-19 disease, has greater Increase in ferritin level compared to the milder form and higher ferritin level on admission has been shown to be associated with poor disease outcome and thus may serve as prognostic indicator of COVID-19. Markers of Coagulopathy

The coagulation abnormality in COVID-19 disease is described as “COVID-19 associated coagulopathy (CAC)”. An increase in D-dimer, prothrombin time, activated partial thromboplastin, and thrombocytopenia are key findings in COVID-19 disease.26 D-dimer level appears to be higher in severe form of COVID-19 disease and is a predictive marker of hospital mortality.27

Cardiac Biomarkers: Cardiac involvement is the most common extra pulmonary presentation in COVID-19 disease, and is associated with increased mortality.28 Acute cardiac injury and heart failure are most frequent events to occur, and the patient is likely to worsen more if there is pre-existing cardiovascular condition.29 Raised cardiac troponin and brain natriuretic peptide (BNP) is seen in patients with SARS-CoV-2.28 Baseline measurement of troponins at the time of hospitalization may be useful, as any increment thereafter is suggestive of possible myocardial injury and may predict disease outcome.

Hepatic Biomarkers: Another clinical manifestation reported in COVID-19 disease is liver injury. The biochemical alteration is seen as elevation in liver enzymes as partate amino transferase (AST), alanine amino transferase (ALT), and lactate dehydrogenase (LDH). At this stage of understanding, this mild elevation in enzymes has been attributed to non-specific response to inflammation.

Renal Biomarkers: Acute kidney Injury (AKI) has emerged as one of the complications of COVID-19. The common cause of AKI in COVID-19 disease has been researched as acute tubular necrosis, while glomerulosclerosis, glomerulonephritis, and glomerulopathy are other pathological features encountered in renal biopsy.32 Characterized by elevated creatinine, increased BUN, proteinuria and hematuria, development of AKI during the hospitalization for COVID-19 disease is associated with further increased risk of mortality.33 Therefore, kidney biomarkers, apart from creatinine, that could detect AKI early may play a vital role in instigating appropriate management to lower the risk. Although not much literature is available about their utility in COVID-19 disease, existing biomarkers like serum Cystatin C, neutrophil gelatinase associated lipocalin (NGAL), Interleukin-18(IL-18), and Kidney injury molecule-1(KIM-1), known for their high sensitivity and specificity in assessment of AKI, may have a role.

Conclusion

NAAT test is currently employed by many private and government laboratories in Nepal for the confirmatory diagnosis of COVID-19 disease. Most of the other biomarkers are readily offered by the laboratories. The behavior of these biomarkers in the context of COVID-19 in our setting is yet to be researched. Nevertheless, from the evidences generated worldwide, these biomarkers can be employed in COVID-19 disease management and improve clinical outcome.

References:

 

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