COVID-19, caused by the SARS-CoV-2 virus, can affect various body systems. This systemic impact often leads to detectable changes in a person’s blood tests. Monitoring these results provides insights into disease severity, progression, and potential complications. These tests do not diagnose COVID-19 on their own, but they are an important part of understanding the illness and guiding medical care.
Changes in Blood Cell Counts
Changes in complete blood count are common in COVID-19 patients. Lymphopenia, a reduced count of lymphocytes (a type of white blood cell), is a notable abnormality. It is characteristic of viral infections, including COVID-19, and a lower count correlates with more severe disease. A count below 1.5 x 10^9/L may indicate increased severity, with severe cases often showing reduced numbers. This reduction, particularly in T-cells, may link to immune system dysregulation.
Total white blood cell count can also alter. While lymphopenia indicates a decrease in a specific white blood cell type, some patients experience neutrophilia (an increase in neutrophils). This can reflect the body’s generalized inflammatory state. Platelet counts, crucial for blood clotting, can also be affected. Thrombocytopenia (low platelet count) is observed in COVID-19 patients, particularly in severe cases. This reduction may be due to factors such as direct infection of bone marrow cells, increased platelet consumption from blood clot formation, or an overactive immune response.
Inflammatory and Clotting Markers
Systemic inflammation and changes in blood clotting are significant aspects of COVID-19, reflected in several markers. C-reactive protein (CRP) and ferritin typically show elevated levels in COVID-19 patients. Higher concentrations of CRP and ferritin associate with increased disease severity and can signal an intense immune reaction, a cytokine storm. In a cytokine storm, the immune system releases an excessive amount of inflammatory proteins, leading to widespread cellular and organ damage.
D-dimer elevation is a frequent and significant finding. D-dimer is a protein fragment produced when a blood clot breaks down; elevated levels indicate increased clot formation and breakdown. This marker highlights hypercoagulability (an increased tendency for blood to clot), a common and concerning complication in severe COVID-19. Markedly elevated D-dimer levels correlate with worse outcomes, including a higher risk of thrombotic events like deep vein thrombosis and pulmonary embolism, and predict increased mortality. Other inflammatory markers like erythrocyte sedimentation rate (ESR) can also be elevated. Procalcitonin might increase, especially if a bacterial co-infection is present.
Indicators of Organ Strain
COVID-19’s systemic nature means it can affect multiple organs, and tests can reveal signs of strain or damage. Liver enzymes, specifically alanine aminotransferase (ALT) and aspartate aminotransferase (AST), often show elevated levels. This can indicate liver inflammation or injury, with elevations reported in a significant percentage of patients. These liver abnormalities are frequently mild and temporary, but their presence can associate with more severe disease progression and complications.
Kidney function can also be compromised, leading to acute kidney injury. Markers like creatinine and blood urea nitrogen (BUN) typically rise when kidney function declines. An increase suggests kidneys are under stress or experiencing damage. Damage can result from direct viral effects on renal cells or indirect mechanisms like systemic inflammation.
The heart can also be impacted. Cardiac markers like troponin and B-type natriuretic peptide (BNP) or its precursor, NT-proBNP, may be elevated. Troponin indicates myocardial injury, stemming from direct viral damage, inflammation, or oxygen supply-demand imbalances. BNP and NT-proBNP are markers of cardiac stretch or strain. Their elevation points to potential cardiac involvement, such as heart muscle inflammation or stress, and often associates with more severe disease and poorer outcomes.
The Bigger Picture: Interpreting Lab Results
No single marker alone definitively diagnoses COVID-19. Instead, healthcare professionals consider patterns of abnormalities across multiple tests for a comprehensive understanding of the disease. These patterns provide insights into illness severity, likely progression, and potential complications. For example, a combination of lymphopenia, elevated inflammatory markers like CRP and ferritin, and high D-dimer levels often points to a more severe disease course.
Medical professionals interpret these results with a patient’s clinical symptoms, physical examination findings, and imaging results (e.g., chest X-rays or CT scans). This integrated approach allows for a more accurate assessment and guides treatment decisions, including hospitalization or specific therapies. These tests are tools for monitoring and managing the illness, not for self-diagnosis.