C-Reactive protein, or CRP for short, is a type of protein produced by the liver in response to inflammation occurring anywhere in the body. When any agent, such as a virus, bacteria, fungus, parasite, or toxic chemicals, enters the body or after an injury, the immune system is directly activated, and immune cells are produced to be sent to the affected area.
In addition, the synthesis of C-Reactive protein in the liver increases, leading to local symptoms like pain, swelling, and redness. Under normal circumstances, the CRP level in the blood of healthy individuals is quite low. However, during any inflammation, the CRP level begins to rise in direct proportion to the severity of the inflammation.
Mild increases in CRP levels in the blood may be due to simple infections that do not cause any symptoms. However, significant and severe elevations in C-Reactive protein levels may indicate serious inflammation, necessitating further investigation.
What is CRP?
In the presence of any inflammation in the body, acute phase reactants in the blood increase, triggering an immune response. One of these protein-based molecules that trigger an inflammatory acute phase response is C-Reactive protein. Known as CRP, this protein increases by at least 25% during an inflammatory condition in the body.
The more severe the inflammation, the higher the CRP level, which is accompanied by symptoms such as swelling, redness, and pain in the affected area. High levels of LDL, also known as bad cholesterol, can also lead to the formation of an acute phase response, resulting in elevated CRP and inflammation.
A variation of the CRP test, called high-sensitivity CRP (hs-CRP), is used to assess the risk of cardiovascular diseases and heart attacks. Apart from infections caused by bacteria, viruses, fungi, or parasites, high CRP levels can also be seen in autoimmune diseases, characterized by the body’s immune response against its tissues, as well as in many chronic and systemic diseases.
When a health screening is performed due to suspicion of any disease or infection, a CRP test is usually included. A significantly elevated CRP level indicates the presence of inflammation in the body. In such cases, further diagnostic tests are conducted to determine the location and cause of the inflammation. Once the underlying health issue is identified and treated, the CRP level can be brought back to a normal range as the inflammation decreases.
If the inflammation is caused by an infection, antibiotics, antiviral, or antifungal medications can be used to eliminate it. In autoimmune diseases, medications that suppress the immune response can control inflammation, thereby balancing CRP levels.
Monitoring the decrease in CRP levels regularly helps evaluate the effectiveness of the treatment plan for inflammation. For example, in antibiotic treatment for an infection, examining whether there is a sufficient decrease in CRP levels can help determine if the medication is effectively addressing the infection. Because of these features, the C-Reactive protein test is one of the most commonly used blood tests in medicine.
What Should the CRP Level Be?
A simple blood test is sufficient to determine the CRP level. A blood sample can be taken from any vein in the body and tested in a laboratory to measure the CRP level easily. No preparation or special equipment is needed for the test. Unlike other values, fasting or being full is not required for this test, meaning it can be conducted at any time of the day.
However, since CRP is often measured along with other blood values, a fasting blood sample may be requested to allow accurate measurement of those other values. Although laboratory criteria may vary, the normal range of C-Reactive protein in the blood is generally expected to be below 1.0 mg/L.
This indicates that the CRP level in the blood of healthy individuals is very low, and any increase is easily noticeable. A CRP level below this threshold suggests that there is no significant inflammation in the body. CRP levels above 1.0 mg/dL indicate an inflammatory condition and require further diagnostic tests.
Mild elevations in CRP are generally not a cause for concern, as they can result from minor inflammations. If such an elevation is detected, additional investigations may be conducted, or follow-up with a repeat blood test may be suggested, considering the patient’s medical history.
In pregnant women and individuals with chronic diseases, even mild elevations in CRP should be taken seriously. In recent years, especially in studies conducted in the United States, it has been proven that patients with elevated CRP levels have a two to three times higher risk of experiencing a heart attack.
While the CRP level alone is not sufficient to diagnose a disease, it can be considered along with other blood findings and test results to evaluate heart attack risk and guide preventive treatments. The risk of cardiovascular disease (CVD) can be assessed using the high-sensitivity hs-CRP level, according to the following scale:
- hs-CRP level below 1.0 mg/dL – Low CVD risk
- hs-CRP level between 1.0 mg/dL and 3.0 mg/dL – Moderate CVD risk
- hs-CRP level above 3.0 mg/dL – High CVD risk
What Causes High CRP Levels?
High CRP levels indicate inflammation in the body, which can occur in any area for various reasons. Elevated CRP indicates the presence and intensity of inflammation and is categorized differently based on the value detected in the blood:
CRP levels between 1-1.5 mg/dL are considered mild elevations and can be caused by:
- Obesity
- Smoking
- Minor injuries
- Colds
- Stress and depression
- Gum infections
- Sleep disorders
- Diabetes
- Pregnancy
CRP levels up to 10 mg/dL are considered moderate elevations, with potential causes including:
- Rheumatoid arthritis
- Heart attack (myocardial infarction)
- Diseases like bronchitis and pancreatitis
CRP levels above 10 mg/dL are classified as significant elevations and indicate severe inflammation in the body. Some conditions that can cause such high CRP levels include:
- Acute bacterial infections (severe elevations above 50 mg/dL are often due to acute bacterial infections)
- Viral illnesses
- Systemic vasculitis
- Major injuries and trauma
What Causes Low CRP Levels?
For healthy individuals, the normal CRP level in the blood is considered to be 1 mg/dL or lower, so low CRP levels are not an issue. A CRP level close to zero or at zero is considered a healthy state, indicating no medical concerns.
If the CRP level in a blood test was previously higher but is lower in a subsequent test, it shows that the inflammation in the body has decreased. Such decreases in CRP are closely monitored, especially during antibiotic trials for acute bacterial infections, to assess the effectiveness of the medication. Therefore, a drop in C-Reactive protein levels is a desirable outcome.
If you notice that your CRP level is above the normal range in a blood test, consult your doctor for more information. If necessary, your doctor may recommend further diagnostic tests to gain insight into your health condition, allowing early detection of potential illnesses.