The COVID-19 infection has been affecting people differently. While some people remain asymptomatic even after contracting the viral disease, others suffer from severe consequences. So far, difficulty in breathing, chest pain, confusion, and bluish discolouration of extremities are considered the clinical signs of severe COVID-19 infection. However, doctors have also reported several cases of respiratory dysfunction and multiple organ failure in COVID-infected people. Some people with COVID-19 infection may develop these severe consequences without exhibiting any symptoms. Hence, diagnostic tests such as D-dimer and Interleukin 6 can help indicate the risk and determine the disease progression.  

What are D-dimer and Interleukin tests?

The D-dimer test involves the identification of a protein called D-dimer in the blood, which is found after the breakdown of a blood clot. Usually, once blood clots are formed inside the body, they start to break down slowly, releasing D-dimer into the blood. High levels of D-dimer in the blood can indicate the production of abnormal clots in the body. 

On the other hand, Interleukin-6 (IL-6) is a protein that is released by the immune cells of the body when fighting bacteria, virus or any other microorganism. High levels of IL-6 in the blood can indicate inflammation, infection, cardiovascular diseases or autoimmune disorders.

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Can D-dimer and interleukin tests determine COVID-19 progression?

Several studies have shown that D-dimer and interleukin tests can help determine the severity of the COVID-19 infection. Some of these studies include:

• Research published in the Biomedical and Biotechnology Research Journal on 13th March 2021 found that people suffering from severe COVID-19 infection exhibited a significant increase in the levels of IL-6, ferritin, CRP, LDH and D-dimer. The scientists further concluded that these tests can be effective in determining the disease severity and progression in COVID-infected people. 
• A study published in the journal Vascular health and risk management in November 2020 concluded that doctors can assess the risk of developing venous thromboembolism (VTE) in critically ill COVID patients by determining the laboratory parameters including D-Dimer, Fibrinogen, and IL-6. VTE is a condition where a blood clot forms in the deep veins of the leg, groin or arm and travels to the lungs resulting in pulmonary embolism. These tests can help in the early diagnosis and prompt treatment of VTE in COVID-19 patients.
• A study published in the journal Life Sciences in August 2020 found that biomarkers such as C-reactive protein, serum amyloid A, IL-6, LDH (lactate dehydrogenase), D-dimer and Platelet count change during the course of COVID-19 disease, especially in severe cases. These tests can help doctors identify the severity of the disease early enough to improve the prognosis of the patient. 
• Similar findings were cited in another study published in the journal Critical Reviews in Clinical Laboratory Sciences. It was found that tests such as IL-6 and D-dimer can help determine the risk of developing severe coagulation-related consequences such as disseminated intravascular coagulation (DIC) and acute respiratory distress syndrome (ARDS) in severe cases of COVID-19 infection.

Who needs to undergo these tests?

A COVID-infected patient would require a D-dimer test if they experience symptoms such as: 

• Difficulty in breathing
• Cough with or without blood
• Swelling, pain, redness and tenderness in the leg
• Increased heart rate
• Chest pain
• Excessive sweating
• Dizziness or fainting

Pregnant women, those who have undergone major surgery (such as hip surgery) or those with pre-existing coagulation disorders may require a D-dimer test if they contract COVID-19 infection.

COVID-19 infected people suffering from pre-existing medical conditions such as diabetes mellitus, hypertension or any cardiovascular disease should get Interleukin 6 test done. Both the tests should be done only after consulting the doctor.

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Conclusion

Several studies have found that the D-dimer and IL-6 test could be effective biomarkers to determine the disease severity and clinical outcome in people with COVID-19. Elevated levels of D-dimer usually indicated that a clot has formed in the body and is in the process of breaking down. This clot can get lodged in the lungs, heart or any other vital organ resulting in pulmonary embolism, cardiac embolism or stroke.

Similarly, a significant increase in the levels of IL-6 can indicate cytokine storm, which has been associated with multiple organ failure in COVID-19 patients. People with COVID-19 must seek medical help immediately if they experience sudden pain in the chest, swelling and tenderness in the legs, and difficulty in breathing.

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