C-reactive protein (CRP) is a substance produced by the liver that acts as a general indicator of inflammation in the body. When tissues are inflamed, the liver releases more CRP into the bloodstream. This protein is measured through a simple blood test, providing a snapshot of inflammatory activity. CRP is a non-specific marker, meaning it signals inflammation but does not pinpoint the exact cause.
Understanding C-Reactive Protein
CRP functions as an acute-phase reactant, meaning its levels can rapidly increase in response to inflammation, infection, or tissue injury. The liver is the primary site of CRP production, increasing its output when stimulated by pro-inflammatory cytokines like interleukin-6. Doctors often order a CRP test to detect inflammation or monitor treatment effectiveness for inflammatory conditions.
For healthy individuals, CRP levels are typically low, usually below 1.0 milligrams per liter (mg/L). Some laboratories may report an upper limit for low-risk inflammation around 3.0 mg/L, or 5.0 mg/L as a broader threshold. These reference ranges can vary slightly depending on the specific laboratory and the assay method used.
How COVID-19 Impacts CRP Levels
In individuals with COVID-19, CRP levels are frequently elevated, particularly in moderate to severe cases. This elevation reflects the systemic inflammatory response triggered by the SARS-CoV-2 virus. Higher CRP concentrations are commonly observed in patients who experience more severe disease progression.
Elevated CRP levels in COVID-19 patients can suggest an increased risk of severe outcomes. These outcomes include progression to acute respiratory distress syndrome (ARDS), a serious lung condition, or the development of a “cytokine storm,” an uncontrolled immune response. Studies show that CRP levels greater than 50 mg/L, and especially above 100 mg/L, are frequently associated with severe COVID-19 cases requiring hospitalization.
While high CRP levels indicate inflammation and disease severity in COVID-19, they are not diagnostic of the virus itself. A high CRP result in the context of COVID-19 must always be interpreted alongside other clinical findings, such as symptoms, imaging results, and specific viral tests.
Interpreting CRP Results and Next Steps
An elevated C-reactive protein level can stem from various causes beyond COVID-19. These include bacterial infections, other viral illnesses, autoimmune disorders like rheumatoid arthritis, chronic inflammatory conditions such as inflammatory bowel disease, and lifestyle factors like obesity and smoking.
A healthcare professional must interpret CRP levels in conjunction with a patient’s complete medical history, current symptoms, and other diagnostic tests. A single CRP value provides only one piece of information and does not offer a complete picture of a person’s health status. Self-diagnosis or attempting to self-treat based solely on CRP levels is not advised.
If you have concerns about your CRP levels, or are experiencing symptoms related to COVID-19 or any other illness, consult your doctor. They can provide an accurate diagnosis, explain what your test results mean, and recommend appropriate next steps for your care.