Hidden inflammation in the body: what CRP, ESR and fibrinogen tests show

These tests appear more and more often on lab results, either as part of routine check-ups or as part of more complex assessments. The main reason is that medicine is increasingly focused on prevention and on finding imbalances in the body early. Chronic inflammation can develop for a long time without clear symptoms, and lab tests can help detect it, although no single test can show it on its own.

CRP, ESR and fibrinogen are used both when looking for the cause of nonspecific symptoms, such as tiredness or persistent pain, and to monitor existing conditions. Their values can raise questions and worries, but it is important to remember that they do not point to a specific disease; they signal an inflammatory process that has to be interpreted in a medical context.

Inflammation is the body’s natural response to harm such as infections, injuries or other damaging factors. In its acute form, inflammation appears quickly and settles once the cause is resolved. Chronic inflammation, on the other hand, is less intense but lasts over time and can affect how the organs work.

When inflammation involves the blood vessels, changes can occur in their inner lining that encourage deposits (plaque) to build up on the artery walls and gradually narrow the arteries. These processes happen slowly and often without obvious symptoms. Tests that detect inflammation can add useful information, but they cannot show on their own whether the arteries are affected. To estimate the risk of heart disease, doctors sometimes use high-sensitivity CRP (hs-CRP) together with the classic risk factors, such as blood pressure, cholesterol, smoking and diabetes.

C-reactive protein is a protein made by the liver when there is inflammation in the body. Its level rises quickly in response to inflammation, whatever the cause. CRP is considered a sensitive marker because it can signal inflammation even when it is mild.

The high-sensitivity form of the test, known as hs-CRP, can detect small changes in inflammation. CRP values can be influenced by infections, chronic conditions, injuries or other factors, which is why the results need careful interpretation. CRP cannot diagnose a condition on its own; it shows how much inflammation there is in the body when the blood sample is taken.

The erythrocyte sedimentation rate (ESR) is a test that has long been used to assess inflammation. ESR measures how quickly red blood cells settle over a set period of time, a process influenced by the changes in blood proteins that occur during inflammation. Although it is a nonspecific test, ESR can give clues about persistent inflammation, especially when it is looked at together with other tests.

Fibrinogen is a protein involved both in inflammation and in blood clotting. High values can point to active or persistent inflammation and can be linked to changes in the properties of the blood, such as higher viscosity. This is why fibrinogen is often checked together with other markers, to get a more complete picture of inflammation in the body.

The results of inflammation tests should not be interpreted on their own. CRP, ESR and fibrinogen values can vary with many factors, including recent infections, chronic conditions or current treatments.

A high value does not automatically mean a serious problem, and a normal value does not always rule out a condition.

Interpreting them correctly means looking at the results together with your symptoms, medical history and other tests. Self-diagnosis can lead to wrong conclusions and needless worry. This is why it is important to discuss your results with a doctor, who can explain them clearly and recommend the next steps, if needed.

Medical sources

• Mayo Clinic: C-reactive protein test
• MedlinePlus: C-Reactive Protein (CRP) Test
• MedlinePlus: Erythrocyte Sedimentation Rate (ESR)
• Mayo Clinic: Sed rate (erythrocyte sedimentation rate)
• MedlinePlus: Fibrinogen blood test
• Arnett DK et al. 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease. Circulation, 2019;140(11):e596-e646