From the Guidelines
Elevated C-Reactive Protein (CRP) levels are primarily caused by inflammation in the body, which can be triggered by various factors including infections, autoimmune disorders, tissue damage, and lifestyle factors. CRP is produced by the liver in response to inflammatory signals, particularly interleukin-6, released during infection, tissue injury, or chronic inflammatory conditions. Common causes of elevated CRP levels include:
- Bacterial infections (like pneumonia, urinary tract infections, or sepsis)
- Viral infections
- Autoimmune disorders (such as rheumatoid arthritis, lupus, or inflammatory bowel disease)
- Tissue damage from surgery or trauma
- Cardiovascular disease
- Lifestyle factors that can raise CRP include obesity, smoking, lack of exercise, and poor diet
- Certain medications like hormone replacement therapy may also increase CRP levels 1. The elevation can be modest (10-40 mg/L) in milder inflammatory conditions or significantly higher (>100 mg/L) in severe bacterial infections. CRP rises rapidly within 4-6 hours of an inflammatory stimulus and can increase thousandfold from baseline levels. It's also important to consider that many factors influence circulating CRP values that are unrelated to “pathological” processes, such as age, sex, socioeconomic status, race, body mass index, exercise, diet, sleep, and medication use 1.
According to a recent study, CRP values greater than 10 mg/L are not always indicative of an ongoing pathological process, and many factors can influence CRP levels 1. For example, a study found that whereas 40% of CRP values >10 mg/L likely were related to acute respiratory infections, 20% seemed to be associated with smoking behavior. It is now clear that many factors influence circulating CRP values that are unrelated to “pathological” processes, and potential guidelines are available for researchers when deciding to include, exclude, and control for these factors 1.
In clinical practice, elevated CRP levels should be interpreted in the context of the patient's overall clinical presentation, and further diagnostic evaluation should be performed to determine the underlying cause of the inflammation. Daily, sequential measurement of inflammatory markers, including CRP, is likely to be of more value in diagnosis of infection than single measurements 1.
From the Research
Causes of Elevated CRP
Elevated C-Reactive Protein (CRP) levels can be caused by various factors, including:
- Infectious diseases, such as bacterial and viral infections 2, 3, 4, 5, 6
- Inflammatory conditions, such as autoimmune disorders and chronic diseases 3
- Acute and chronic responses to tissue damage or inflammation 3
Infectious Causes
Infectious diseases that can cause elevated CRP levels include:
- Bacterial respiratory infections, such as pneumonia 2, 6
- Viral respiratory infections, such as influenza and COVID-19 2, 3, 6
- Atypical bacterial infections, such as Legionella pneumophila and Mycoplasma pneumoniae 4
- Viral infections, such as Dengue virus, Cytomegalovirus, and Epstein Barr virus 4
Non-Infectious Causes
Non-infectious causes of elevated CRP levels include:
- Chronic inflammatory diseases, such as arthritis and cardiovascular disease 3
- Tissue damage or inflammation, such as trauma or surgery 3
- Macrophage activation syndrome, which can contribute to disease progression in COVID-19 3
Diagnostic Considerations
When interpreting CRP levels, it is essential to consider the clinical context and other diagnostic parameters, such as: