CRP (C-Reactive Protein) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is CRP (C-Reactive Protein)?

C-reactive protein (CRP) is a protein produced by the liver in response to inflammation. It is one of the most widely used biomarkers in clinical medicine and serves as a general indicator of inflammation and infection throughout the body. CRP is classified as an acute-phase reactant - a protein whose blood concentration rises rapidly and significantly in response to tissue injury, infection, or inflammation.

CRP was first discovered in 1930 by researchers who found it in the blood of patients with pneumococcal pneumonia. It was named for its ability to react with the C-polysaccharide of Streptococcus pneumoniae. Since then, it has become one of the most commonly ordered blood tests worldwide.

When your body detects tissue damage, infection, or inflammatory signals, immune cells release cytokines, particularly interleukin-6 (IL-6), that signal the liver to ramp up CRP production. CRP levels can rise by as much as 1,000-fold within 24–48 hours of an acute inflammatory stimulus, making it an extraordinarily sensitive marker of systemic inflammation.

CRP serves several biological functions: it activates the complement system (part of the immune response), helps the immune system clear dead and dying cells, and promotes phagocytosis (the engulfing and digestion of pathogens by immune cells). In other words, CRP is not merely a marker of inflammation - it is an active participant in the immune response.

There are two types of CRP test used in clinical practice:

• Standard CRP: Measures CRP across a broad range (typically 5–300+ mg/L). Used to detect and monitor significant inflammation, infection, and inflammatory disease.
• High-sensitivity CRP (hs-CRP): Measures very low levels of CRP (typically 0.1–10 mg/L). Used primarily for cardiovascular risk assessment, where even slight chronic inflammation contributes to atherosclerosis.

Why Is CRP Tested?

CRP is one of the most versatile blood markers, tested across numerous clinical scenarios:

• Detecting infection: CRP rises rapidly in bacterial infections and is used to differentiate bacterial from viral infections (which tend to produce a smaller CRP response). It is particularly useful in diagnosing pneumonia, urinary tract infections, sepsis, and appendicitis.
• Monitoring inflammatory disease: CRP tracks disease activity in conditions such as rheumatoid arthritis, inflammatory bowel disease (Crohn's disease and ulcerative colitis), polymyalgia rheumatica, and vasculitis.
• Post-surgical monitoring: CRP normally rises after surgery and then falls as healing progresses. A secondary rise suggests post-operative infection or complications.
• Cardiovascular risk assessment (hs-CRP): Chronic low-grade inflammation is a key driver of atherosclerosis. Multiple large studies, including the JUPITER trial, have demonstrated that hs-CRP independently predicts heart attacks, strokes, and cardiovascular death, even in people with normal cholesterol levels.
• Guiding antibiotic therapy: CRP trends (rather than single values) help clinicians decide when to start, continue, or stop antibiotics.
• Cancer screening and monitoring: Persistently elevated CRP without an obvious cause may prompt investigation for occult malignancy. CRP also correlates with prognosis in several cancers.
• Differentiating organic from functional conditions: In patients with abdominal symptoms, a normal CRP helps distinguish irritable bowel syndrome (functional) from inflammatory bowel disease (organic).

Normal CRP Ranges

CRP is measured in milligrams per litre (mg/L):

CRP Level	Interpretation
Less than 5 mg/L	Normal (standard CRP)
5–10 mg/L	Mild inflammation (may be normal in some individuals)
10–50 mg/L	Moderate inflammation (bacterial infection, active inflammatory disease)
50–100 mg/L	Significant inflammation (severe bacterial infection, acute flare of inflammatory disease)
Greater than 100 mg/L	Severe inflammation (sepsis, major trauma, severe bacterial infection)
Greater than 200 mg/L	Very severe inflammation (sepsis, extensive burns, severe pancreatitis)

High-sensitivity CRP (hs-CRP) for cardiovascular risk

hs-CRP Level	Cardiovascular Risk
Less than 1.0 mg/L	Low risk
1.0–3.0 mg/L	Moderate risk
Greater than 3.0 mg/L	High risk
Greater than 10 mg/L	Likely reflects acute inflammation rather than chronic cardiovascular risk - recheck when acute illness has resolved

It is important to note that a single CRP reading above 10 mg/L should not be used for cardiovascular risk assessment, as it likely reflects an acute inflammatory process. The test should be repeated after 2–3 weeks once any acute illness has resolved.

What Do High CRP Levels Mean?

Elevated CRP indicates that inflammation is present somewhere in the body. The degree of elevation and the clinical context help narrow down the cause:

Infectious causes

• Bacterial infections: CRP rises rapidly and significantly (often above 50 mg/L) in bacterial pneumonia, urinary tract infections, cellulitis, appendicitis, meningitis, and sepsis. CRP above 100 mg/L is strongly suggestive of bacterial infection.
• Viral infections: Typically produce a more modest CRP response (usually below 40 mg/L), though some severe viral infections (influenza, COVID-19) can cause higher elevations.
• Fungal and parasitic infections: Can elevate CRP, particularly in immunocompromised patients.

Inflammatory and autoimmune conditions

• Rheumatoid arthritis: CRP correlates with disease activity and joint inflammation.
• Inflammatory bowel disease: Crohn's disease typically produces a more significant CRP response than ulcerative colitis.
• Polymyalgia rheumatica and giant cell arteritis: Often present with very high CRP (above 50 mg/L) alongside an elevated ESR.
• Systemic lupus erythematosus (SLE): Interestingly, CRP is often only mildly elevated in SLE flares (CRP is typically below 30 mg/L). A very high CRP in a lupus patient should raise suspicion for concurrent infection.
• Gout: Acute gout attacks cause significant CRP elevation.
• Ankylosing spondylitis: CRP helps monitor disease activity.

Other causes

• Surgery and trauma: CRP peaks 48–72 hours after surgery and gradually normalises over 1–2 weeks.
• Myocardial infarction: Heart attacks cause tissue injury that raises CRP.
• Cancer: Lymphoma, renal cell carcinoma, and advanced solid tumours can cause persistently elevated CRP.
• Obesity: Adipose tissue produces IL-6, driving chronic low-grade CRP elevation. Obese individuals commonly have hs-CRP levels of 3–10 mg/L.
• Smoking: Chronic inflammation from smoking raises hs-CRP.
• Chronic kidney disease: Associated with chronic inflammation and elevated CRP.
• Obstructive sleep apnoea: The intermittent hypoxia and sympathetic activation in sleep apnoea drive systemic inflammation.
• Depression: Moderate depression has been associated with elevated hs-CRP, suggesting a link between mental health and inflammation.

What Do Low CRP Levels Mean?

A low or undetectable CRP is generally reassuring and indicates an absence of significant systemic inflammation. There is no condition associated with "too low" CRP - the lower, the better.

A normal CRP has good negative predictive value, particularly in:

• Ruling out serious bacterial infection: A CRP below 20 mg/L within 24 hours of symptom onset makes severe bacterial infection less likely (though not impossible in very early infection).
• Differentiating IBS from IBD: A normal CRP in a patient with chronic bowel symptoms supports a diagnosis of irritable bowel syndrome over inflammatory bowel disease.
• Cardiovascular risk: An hs-CRP below 1.0 mg/L is associated with low cardiovascular risk.

How to Lower Your CRP Levels

Reducing CRP means addressing the underlying inflammation. For acute infections and inflammatory flares, medical treatment is primary. For chronic low-grade inflammation (as measured by hs-CRP), lifestyle interventions are highly effective:

Lifestyle strategies

• Lose excess weight: Weight loss is one of the most powerful ways to reduce hs-CRP. Studies show that losing 5–10% of body weight can reduce CRP by 30–40%. Visceral fat is particularly inflammatory.
• Exercise regularly: Regular aerobic exercise (150+ minutes per week) consistently reduces CRP, independently of weight loss. The anti-inflammatory effects of exercise are well-documented across hundreds of studies.
• Eat an anti-inflammatory diet: The Mediterranean diet, rich in olive oil, oily fish, fruits, vegetables, nuts, and whole grains, significantly reduces CRP. Conversely, diets high in processed food, refined sugar, and saturated fat are pro-inflammatory.
• Increase omega-3 fatty acids: Oily fish (salmon, mackerel, sardines) and omega-3 supplements (2–4 g/day of EPA/DHA) have been shown to reduce CRP.
• Quit smoking: Smoking cessation reduces CRP within weeks. It is one of the most impactful changes you can make for inflammatory and cardiovascular health.
• Prioritise sleep: Sleep deprivation and poor sleep quality are associated with elevated CRP. Aim for 7–9 hours per night.
• Manage stress: Chronic psychological stress activates inflammatory pathways. Meditation, mindfulness, and regular physical activity help mitigate this.
• Reduce alcohol: Heavy drinking promotes inflammation, while moderate consumption (within NHS guidelines) appears to have a neutral or mildly anti-inflammatory effect.
• Increase fibre intake: Dietary fibre from whole grains, legumes, and vegetables is associated with lower CRP in population studies.

Medical interventions

• Statins: Beyond lowering LDL cholesterol, statins reduce CRP - an effect that contributes to their cardiovascular benefit. The landmark JUPITER trial demonstrated that rosuvastatin reduced cardiovascular events in patients with elevated hs-CRP but normal LDL cholesterol.
• Treating underlying conditions: Effective treatment of rheumatoid arthritis, inflammatory bowel disease, periodontitis, and infections naturally reduces CRP.
• Colchicine: The COLCOT trial showed that low-dose colchicine reduces cardiovascular events, partly through CRP reduction.

When Should You Get Tested?

Consider CRP or hs-CRP testing if you:

• Have symptoms of infection (fever, pain, malaise)
• Have a chronic inflammatory condition that requires monitoring (RA, IBD, vasculitis)
• Are recovering from surgery and concerned about complications
• Want to assess your cardiovascular risk (hs-CRP), especially if you have borderline risk factors
• Are overweight, smoke, or have a sedentary lifestyle and want to assess chronic inflammation
• Have a family history of heart disease
• Have unexplained fatigue, weight loss, or persistent symptoms without a clear diagnosis

For cardiovascular risk assessment, hs-CRP should be measured when you are feeling well - not during acute illness. If the result is above 10 mg/L, repeat the test after 2–3 weeks.

Which Lola Health Tests Include CRP?

CRP is included in several Lola Health panels:

• Peak Insights (70 Biomarkers) - Our most comprehensive panel, including hs-CRP for cardiovascular risk alongside full metabolic, hormonal, and nutritional markers.
• Vital Check (56 Biomarkers) - Broad health screen including CRP and inflammatory markers.
• Core Health (45 Biomarkers) - Essential health markers including CRP.
• Heart Health Blood Test - Focused cardiovascular panel including hs-CRP, lipids, and apolipoproteins.

All Lola Health tests use a venous blood draw at one of our nationwide partner clinics — never a finger prick. Results are reviewed by a doctor and returned within 4 working days.