High CRP: What It Means and What to Do Next

Introduction: The body's inflammatory smoke alarm

C-reactive protein (CRP) is often described as the body's "smoke alarm." Produced by the liver, its levels rise sharply and quickly whenever inflammation occurs anywhere in the body. Whether you are fighting a minor viral infection, recovering from a physical injury, or managing a chronic autoimmune condition, CRP serves as a sensitive, non-specific indicator that your immune system is in an active state.

While a high CRP result can be concerning to see on a lab report, it is important to understand that the test itself does not provide a diagnosis. It tells your doctor that there is inflammation, but not where it is or what is causing it. A result of 15 mg/L might be due to a common cold, while a result of 150 mg/L usually signals a more significant bacterial infection or severe inflammatory flare.

In this guide, we will break down the typical reference ranges, explore the most common reasons for both acute and chronic elevations, and discuss how CRP is used alongside other markers like ferritin and the full blood count. We will also outline the "red flags" that mean a high CRP requires immediate medical attention and when it is appropriate to monitor the level over time.

Understanding the context of your CRP result — including any symptoms you have and your overall medical history — is the key to moving from a confusing number to an actionable health plan. For those tracking their long-term health, understanding how CRP reflects lifestyle factors can also be highly valuable.

What is CRP and what does a high result mean?

CRP (C-reactive protein) is a protein made by your liver in response to signals from inflammatory cells. It rises quickly — often within 6 to 48 hours — when your body is fighting infection, injury, or autoimmune activity. Because it responds so rapidly, it is an excellent tool for monitoring the "activity" of a condition or the effectiveness of a treatment.

Typical reference ranges (mg/L):

Less than 5 — Considered normal for most healthy adults.
5–10 — Mild elevation; often seen in smokers, obesity, or very minor infections.
10–100 — Moderate inflammation; common in viral infections, autoimmune flares, or after surgery.
Greater than 100 — Significant elevation; often indicates a serious bacterial infection (like pneumonia or sepsis) or severe inflammatory disease.

Reference ranges vary by laboratory — always read your result against your own lab's specific values.

It is also important to distinguish between standard CRP and hs-CRP (high-sensitivity CRP). While standard CRP is used to look for significant inflammation, hs-CRP is a more precise test used to measure very low levels of inflammation, primarily to assess cardiovascular risk.

Common causes of a raised CRP

Because CRP is a general marker, its list of potential causes is long. Doctors group these into acute (sudden) and chronic (long-term) causes:

Infections: Bacterial infections usually cause higher CRP spikes than viral infections. Conditions like urinary tract infections (UTIs), pneumonia, and skin infections (cellulitis) are common culprits.
Autoimmune and Inflammatory Diseases: Rheumatoid arthritis, lupus, and inflammatory bowel disease (Crohn's or Ulcerative Colitis) often lead to persistent or fluctuating CRP levels.
Injury and Surgery: Any significant physical trauma or surgical procedure will cause a predictable spike in CRP as the body begins the healing process.
Lifestyle and Metabolic Factors: Obesity, smoking, and lack of exercise are associated with "chronic low-grade inflammation," where CRP sits persistently between 3 and 10 mg/L.
Chronic Conditions: Uncontrolled high blood pressure and diabetes can also contribute to mildly elevated levels.

CRP is often checked alongside ferritin and liver enzymes to build a fuller picture of what's causing your symptoms.

How your doctor will investigate a raised CRP

A raised CRP is a starting point, not a destination. Your doctor will use the "clinical context" — your symptoms, age, and history — to decide the next steps. They focus on how high it is, how quickly it changes, and what other tests show.

Common follow-up investigations include:

Full Blood Count (FBC): Checking the white blood cell count can help confirm an infection.
Procalcitonin: A more specific marker that helps distinguish bacterial from viral infections.
Imaging: Such as a chest X-ray if you have a cough, or an ultrasound if you have abdominal pain.
Repeat Testing: In many mild cases, the best "test" is to repeat the CRP in 1–2 weeks to see if it is trending down.

Important: If your CRP is high but you feel completely well, your doctor may simply repeat the test in a few weeks. Many minor elevations resolve on their own without treatment.

When to seek medical care

Seek emergency care (A&E) if a high CRP is accompanied by:

High fever (above 39°C) or feeling very cold and shivery
Confusion, disorientation, or slurred speech
Severe shortness of breath or chest pain
Mottled or pale skin, or a rash that doesn't fade under a glass
Severe abdominal pain or inability to pass urine

Book a GP appointment for:

A CRP result that remains high (above 10 mg/L) for more than 4 weeks
Persistent joint pain, stiffness, or swelling
Unexplained fatigue, night sweats, or weight loss
Recurring symptoms that seem to track with your CRP levels

Frequently Asked Questions

Can stress raise my CRP?

Chronic psychological stress can contribute to low-grade inflammation (often between 3–6 mg/L). However, a significant spike (e.g., over 20 mg/L) is usually due to a physical cause like infection or injury.

Can intense exercise affect the result?

Yes. Strenuous exercise, like running a marathon or heavy weightlifting, causes temporary muscle damage and inflammation. This can raise CRP for 2–4 days after the activity.

Does a high CRP mean I have cancer?

Not necessarily. While some cancers can raise CRP, it is far more commonly caused by infections or autoimmune conditions. CRP is a very poor screening tool for cancer on its own.

How can I naturally lower my CRP?

For chronic low-grade inflammation, lifestyle changes can help: maintaining a healthy weight, quitting smoking, eating an anti-inflammatory diet (like the Mediterranean diet), and regular moderate exercise.

Is a high CRP result dangerous during pregnancy?

CRP levels can naturally be slightly higher during pregnancy. However, a significant elevation requires careful review by your midwife or obstetrician to rule out infection.

Why did my doctor check CRP instead of ESR?

CRP and ESR (Erythrocyte Sedimentation Rate) both measure inflammation. CRP is generally preferred because it rises and falls more quickly, giving a more "up-to-date" picture of your health.

Can dehydration affect my CRP levels?

Severe dehydration can concentrate proteins in the blood, potentially making a result look slightly higher than it is, but it won't cause a major elevation on its own.

Should I worry about a CRP of 6 mg/L?

A result of 6 mg/L is only slightly above the typical threshold of 5 mg/L. In the absence of symptoms, this is often considered a "borderline" finding that may just need monitoring.

Does fasting improve CRP levels?

Fasting is not required for a CRP test. However, long-term healthy eating patterns can help lower your baseline chronic inflammation.

Can a dental infection raise CRP?

Yes. Abscesses, significant gum disease, or recent dental surgery are common but often overlooked causes of raised inflammatory markers.

Related Blood Test Guides

Explore related blood test guides to better understand your results in context.

Blood test results are often best understood alongside related markers and patterns. You can explore the guides above or upload your full lab report for more structured interpretation.