CRP and ESR Tests: What Inflammatory Markers Reveal About Your Health

15 Oct 2025

Inflammation is the body’s natural defence response to infection, injury, or harmful stimuli. However, persistent inflammation without an obvious cause may indicate an underlying health condition that requires medical assessment. C-reactive protein (CRP) test and the erythrocyte sedimentation rate (ESR) test are two of the most common blood tests used to assess inflammation. 

If you are not sure if your symptoms warrant testing, you can schedule an appointment with our London GP Clinic to receive tailored advice and rapid access to investigations.

What are Inflammatory Markers?

Inflammatory markers are substances in the blood that rise when the body is fighting infection, healing from injury, or responding to inflammation. They are indirect indicators of inflammation used by doctors to support diagnosis. They cannot diagnose a condition specifically, but they will assist with the investigation. 

• C-reactive protein (CRP): A protein produced by the liver that rises sharply in response to inflammation.
• Erythrocyte sedimentation rate (ESR): This test evaluates how fast red blood cells settle in a tube (a process called sedimentation), where quicker rates correlate with higher levels of inflammation.

If you would like these markers tested along with more general health checks, you can visit our page for packages and individual tests with quick turnaround times.

CRP Blood Test: Explained

How it Works

CRP is an acute-phase protein, which suggests it can rise within a few hours of an injury or infection. An elevated CRP indicates that the immune system is actively responding to infection, injury, or inflammation.

What it May Indicate

Elevated CRP may be related to:

• Bacterial infections (like pneumonia)
• Autoimmune diseases (such as lupus or rheumatoid arthritis)
• Inflammatory bowel disease (IBD)
• A mild but persistent rise in CRP is associated with an increased risk of cardiovascular disease
• Trauma or inflammation following surgery

Typical Reference Values (lab ranges may vary)

• Normal CRP level: often below 5 mg/L
• Mild rise: approximately 5–50 mg/L
• Marked rise: 100 mg/L or greater (usually associated with severe bacterial infection)

If you are not sure whether to order an isolated CRP test or a larger panel test, it is often best to book a same-day appointment with a doctor for a tailored approach to your testing, symptoms and medical history.

ESR Blood Test: Explained

How it Works

ESR measures how fast red blood cells clump and then fall (i.e., sediment) in a standard tube using graduated markings. Inflammation alters blood proteins, which causes red cells to clump and fall faster.

What it May Indicate

An elevated ESR may be suggestive of:

• Chronic infections
• Autoimmune diseases (such as polymyalgia rheumatica or vasculitis)
• Certain types of anaemia or kidney disease can independently elevate ESR, even without active inflammation
• Persistent inflammatory joint diseases

Typical Reference Points (age/sex dependent)

• Men under 50: around 0–15 mm/hr
• Women under 50: around 0–20 mm/hr
• Older adults may have elevated ESR values

Most of our health screening packages include ESR along with comprehensive blood tests, making it easy to assess inflammation and organ function together.

CRP vs. ESR: Major Contrasts      

Doctors will commonly order both of these tests simultaneously as they provide good complementary information. If you’re unsure which test is more appropriate, your GP can provide a clinical assessment and recommend the most suitable option.

When Should I Get Tested?

Ask about CRP or ESR if you have:

• Persistent fever or an unexplained ongoing illness
• Stiffness, joint pain and swelling
• Chronic fatigue or unexplained weight loss
• Digestive problems with possible inflammatory bowel disease
• Symptoms of autoimmune conditions (like excessive tiredness, multi-joint pain or rashes)
• Follow-up for established conditions (like arthritis) or after a procedure

Prefer to do everything in one visit? You can directly book private blood tests without consulting first, and most things are ready quickly, with GP review after for a result interpretation and further guidance.

Factors that may affect your results

CRP and ESR tests cannot diagnose anything by themselves. Factors affecting your results include:

• Pregnancy (higher ESR)
• Temporary viral illnesses (short-term increases)
• Chronic conditions like diabetes or obesity, affecting the baseline CRP
• Varying results across different labs (reference ranges differ)

A same-day GP can review your symptoms, medical history, and medications to determine whether further tests or imaging are needed.

Common conditions with CRP & ESR

• Rheumatoid arthritis and inflammatory arthritis: monitoring disease activity and flare-ups
• Polymyalgia rheumatica and vasculitis: ESR is often very raised
• Acute infections: CRP helps manage the severity and response to treatment
• Chronic liver or kidney disease: impact inflammatory profiles
• Cardio-metabolic risk: association with long-term risk.

For organ-specific assessment, your healthcare professional may add tests such as thyroid, kidney, or liver function profiles when clinically indicated.

What to Do If Your CRP or ESR Is Elevated

1. Don’t panic — an elevated result suggests taking a closer look, not necessarily diagnosing.
2. Depending on the recent medical history, it may be suggested that you be retested within a short period of time, especially if you have had an upper respiratory tract infection.
3. Further investigations may include urine or stool tests, autoimmune panels, imaging or referrals to specialists.
4. Lifestyle modifications:

• Focus on legumes, whole grains, vegetables and oily fish.
• Stay active (try and get some regular moderate exercise).
• Get 7 to 9 hours of consistent sleep.
• Don’t smoke and limit alcohol.

You can book a Private GP consultation for once you are ready to consider treatment and interpret all your results (for example from blood tests). If time is limited or you need urgent review, our same-day doctor service can provide prompt assessment and guidance.

What is the most convenient way to assess inflammation?

If you are concerned about symptoms or want to be proactive about your health, you can consider the following packages: 

• Health screening packages (like Well-Man or Well-Woman, Full Body MOT) offer a quick and convenient way to complete a comprehensive health assessment, including organ panels and ESR/FBC.
• Private blood tests with targeted tests such as FBC, CRP, thyroid, liver and kidney assessments which give rapid results.
• Prefer to speak to someone first? Contact our London GP Clinic for personalised advice and a clear, tailored testing plan.

FAQs

Is a referral needed?

No, you can directly schedule a blood test or health screening, or speak to a GP in advance, if preferred.

Is ESR included in packages?

Yes, several blood tests and screening packages have ESR/FBC included in core markers.

How quickly do results return?

The results of most blood tests are available in 24 to 48 hours. Visit our blood tests page for details and bookings.