The liver makes C-reactive protein (CRP) in response to inflammation in the body. The CRP test measures the amount of this protein in the blood. High levels of CRP can indicate inflammation due to an acute or chronic condition.

A wide variety of inflammatory conditions can cause elevated CRP levels, including:

High CRP levels are nearly always a sign of a serious underlying medical condition. Slight and moderate elevations of 0.3–1.0 milligrams per deciliter (mg/dl), may happen in pregnant individuals and people with mild infections, diabetes, and some other medical conditions.

The most common cause of high CRP levels is a severe infection. Other possible causes include a poorly controlled autoimmune disease and severe tissue damage.

Read on to learn more about CRP levels, including how doctors check these levels, the normal ranges, and what can cause elevated levels in the body.

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The CRP test is a type of blood test.

There is no need to fast or avoid liquids before having a CRP test. However, people having a high sensitivity CRP (hs-CRP) test may have other blood tests at the same time, and these may require fasting for 9–12 hours beforehand.

hs-CRP

While both tests measure the levels of the same molecule in the blood, the hs-CRP test is different than the CRP test.

The hs-CRP test detects small increases of CRP in the bloodstream. It generally measures lower levels of the CRP molecule than the CRP test.

Doctors will use the hs-CRP test to evaluate a healthy person’s risk of developing cardiovascular disease and other heart conditions.

Some conditions and factors that may cause an elevated hs-CRP level include:

Obtaining the sample for both CRP tests involves a blood draw, which usually takes just a few minutes.

The symptoms of elevated CRP levels depend on the underlying condition that is causing them.

However, many people with moderate infections or injuries or conditions that cause chronic inflammation may experience similar symptoms. These include:

  • unexplained exhaustion
  • pain
  • muscle stiffness, soreness, and weakness
  • low grade fever
  • chills
  • a headache
  • nausea, loss of appetite, and indigestion
  • difficulty sleeping or insomnia
  • unexplained weight loss

People with very high CRP levels often have an acute infection.

The symptoms of acute infection include:

  • high fever
  • rapid heart rate
  • uncontrollable sweating, chills, or shaking
  • uncontrollable or persistent vomiting, retching, or diarrhea
  • difficulty breathing
  • rash or hives
  • parched lips, mouth, and skin
  • dizziness or lightheadedness
  • a severe headache, body pain, stiffness, or soreness
  • loss of consciousness

Some people with high CRP may have few or no symptoms, especially in the early stages of heart disease.

There is currently no set standard for CRP blood levels, and different labs may have slightly different guidelines. This means that a slight elevation in CRP levels could mean nothing.

However, as a general rule, the following classifications apply to CRP:

  • Minor elevation refers to levels between 0.3 mg/dl and 1.0 mg/dl. This can occur in people who are sedentary, pregnant, or living with a chronic condition, such as diabetes. Mild infections such as the common cold may also trigger these elevations.
  • Moderate elevation refers to levels between 1.0 mg/dl and 10.0 mg/dl, which can signal a more significant issue. A moderate elevation may be due to acute inflammation from an infection or chronic inflammation from a serious disease, such as RA or heart disease.
  • Severe elevation refers to levels above 50.0 mg/dl. This elevation warns of an acute bacterial infection.

CRP levels above 10.0 mg/dl — called marked elevation — will typically indicate an underlying inflammatory issue.

The hs-CRP test results indicate a person’s risk of developing cardiovascular disease, with the following ranges:

  • less than 2 mg/l indicates a lower risk
  • greater than 2 mg/l indicates a higher risk

CRP levels that are mildly or moderately elevated can be hard to interpret.

A huge range of conditions can raise CRP levels slightly. As there is no standard reference range for CRP, there is usually no way to draw any conclusions by looking at CRP levels alone.

The following factors can also make it challenging to interpret CRP levels:

  • Lifestyle: People who smoke, have obesity, or do little exercise may have higher-than-normal CRP levels.
  • Minor injuries or infection: These conditions may temporarily raise CRP levels and conceal other potential conditions, such as diabetes or IBD.
  • Chronic conditions: Conditions that cause persistent inflammation, including autoimmune diseases, may mask other possible causes of elevated CRP, such as a minor infection.
  • Estrogen levels: Estrogen-based medications such as birth control pills and hormone replacement medications may raise CRP levels.
  • Pregnancy: Pregnancy can elevate CRP levels, especially during the later stages.

A doctor will usually order a CRP test alongside several other tests to get a broad overview of a person’s health. This will allow them to consider a range of medical factors.

A doctor will also often wish to repeat the test to see how CRP levels change over time before they make a diagnosis.

However, regardless of any other external factors, CRP levels above 10 mg/l will typically indicate an underlying inflammatory issue.

Chronically elevated CRP levels often signal RA or infectious arthritis, which occurs when a joint becomes infected.

Significantly elevated CRP levels tend to occur with severe infections, such as bacterial or fungal infections. Bacterial infection is responsible for about 90% of the cases involving CRP levels higher than 50 mg/l.

Sometimes, higher levels also occur with certain cancers and other conditions that can cause significant inflammation.

A CRP test requires only a blood draw from a vein. These tests pose very little risk to the person and are generally safe.

A person is likely to experience a pricking sensation when a technician inserts the needle. The site of the needle insertion may continue to throb or sting during the blood draw and possibly for some time afterward.

Some people also have these symptoms after a blood draw:

  • bruising at the site of the blood draw
  • dizziness or fainting during or after the test
  • soreness at the site of the blood draw

People with bleeding disorders may have excessive bleeding after the blood draw. A person should let the healthcare professional know if they have a history of bleeding disorders or excessive bleeding.

A doctor may recommend a CRP test based on a person’s other symptoms or as a follow-up to other blood work.

A person who has signs of acute inflammation may be very sick with symptoms of infection. Chronic inflammation may cause chronic health conditions, such as pain or heart health issues. A person with either group of symptoms might need the test.

A person may undergo the test at the doctor’s office, or they might go to a lab. It does not require any special preparation and is safe for anyone who does not have a serious bleeding disorder.

During the procedure, a technician — usually a phlebotomist — will wrap a rubber band around the person’s arm, just above their elbow. Next, they may tap on the veins or ask a person to make a fist to make the veins more visible. They will then puncture a vein with a small needle and allow blood to flow into a test tube.

Sometimes a person might choose to have the blood drawn from a vein elsewhere in the body. Some people feel dizzy or faint during or after the blood draw. People who faint during blood draws may ask to lie down during or after the procedure.

Very high CRP levels may signal a medical emergency, and a person may need prompt care in the hospital.

However, if a person’s CRP level is only moderately elevated, determining the cause can be difficult, especially if there are few or no symptoms. A doctor may recommend the following:

  • additional tests for potential causes
  • follow-up testing in 1–2 months
  • monitoring for other symptoms

A person should tell the doctor about their health history and any recent symptoms they have experienced, as this information might aid the diagnosis.

Doctors use CRP and hs-CRP tests to detect the levels of CRP in the body. Elevated levels of the protein may indicate an underlying condition or a higher risk of cardiovascular disease. The treatment for elevated levels will differ depending on the cause.

Sometimes, elevated CRP does not require any treatment. This is most common when there is a temporary elevation because of pregnancy, a mild infection, or a physical injury.

People with elevated CRP should follow up with a healthcare professional to discuss the next steps and reduce their risk of serious health issues.

A range of conditions can cause mildly or moderately raised CRP levels, but very high CRP levels are generally easier to interpret.