hs-CRP: What an Inflammation Blood Test Shows

Why this matters

Inflammation is the body's response to infection, injury or irritation, and can cause heat, swelling and pain. CRP is one of the most widely used blood tests for it. It is checked in infections, in many immune conditions and as part of general health screening. Understanding what it can and cannot show helps make sense of a result that comes back raised, or normal when you feel unwell.

What CRP is

C-reactive protein is made by the liver in response to signals released during inflammation. Levels can rise within hours of an infection or injury and fall again as the inflammation settles.

Standard CRP and high-sensitivity CRP

A standard CRP test is designed to pick up the larger rises seen in infection or active inflammatory disease. A high-sensitivity CRP (hs-CRP) test measures the same protein but can accurately detect much lower levels. This makes it useful for spotting mild, long-lasting (low-grade) inflammation that a standard test might report simply as normal.

What can raise CRP

CRP is a general marker. It can be raised by infections, injuries and surgery, flare-ups of inflammatory conditions such as rheumatoid arthritis or inflammatory bowel disease, and by factors such as smoking, carrying excess weight and poor sleep. Even a recent cold can raise it for a short time. For that reason, a single raised result is usually repeated once any short-term illness has passed.

Why a normal CRP does not rule everything out

Some immune conditions do not raise CRP much, even when they are active. In lupus, an autoimmune condition that can affect the joints, skin and organs, CRP often stays fairly normal during a flare (a period when symptoms get worse) unless there is infection or certain types of inflammation. Clinicians often look at CRP alongside other markers, such as ESR (erythrocyte sedimentation rate, another general blood test for inflammation), and at how you feel.

What you could do

CRP is most useful as a trend rather than a single number.

• Test when you are free of colds and other short-term illness if you want a baseline, a starting result to compare future tests against
• Note anything that might have affected the result, such as a recent infection, injury or very intense exercise
• Track results over time alongside symptoms and flares, and discuss any persistent rise with your GP

This article is for general information only and is not a substitute for medical advice. If you are worried about your health or your results, speak to your GP or specialist team. In an emergency, call 999 or go to A&E.

References:

NHS, 'Blood tests' https://www.nhs.uk/tests-and-treatments/blood-tests/

NHS, 'Lupus' https://www.nhs.uk/conditions/lupus/