CRP blood test: what it measures and how to read your results

A C-reactive protein (CRP) test is a blood test that measures levels of a protein produced by the liver in response to inflammation. It's one of the most commonly ordered inflammatory markers — used to help diagnose infections, monitor chronic inflammatory conditions, and assess cardiovascular risk. Understanding your CRP results can help you and your provider make more informed decisions about your care.

What is C-reactive protein?

CRP is a protein your liver releases rapidly when there is inflammation anywhere in the body — such as during an infection, an autoimmune flare, or tissue injury. Unlike many lab values, CRP can rise within a few hours of an inflammatory trigger and then fall quickly once the trigger resolves. This responsiveness makes it a useful real-time marker of acute inflammation.¹

Standard CRP vs. high-sensitivity CRP (hs-CRP)

There are two types of CRP tests in common use:

• Standard CRP detects moderate-to-high levels of inflammation (typically greater than 1 mg/L) and is used to detect active infections, monitor autoimmune diseases, or investigate unexplained symptoms.
• High-sensitivity CRP (hs-CRP) measures very low levels of CRP and is used specifically to assess cardiovascular risk. Persistently elevated hs-CRP — even in the absence of obvious illness — is associated with increased risk of heart attack and stroke.²

The two tests serve different clinical purposes and are not interchangeable. Your provider will order whichever is appropriate based on your situation.

How to read your CRP results

Reference ranges for standard CRP vary by lab, but general interpretation follows this pattern:

• Normal: below 1.0 mg/L — no significant inflammation detected
• Mild elevation: 1–3 mg/L — mild inflammation; may need follow-up depending on symptoms
• Moderate elevation: 3–10 mg/L — suggests active inflammation from infection, injury, or chronic disease
• High: above 10 mg/L — significant inflammation; commonly seen with bacterial infections, major trauma, or serious autoimmune flares
• Very high: above 100 mg/L — typically indicates serious bacterial infection

A single CRP value is rarely interpreted in isolation. It should always be considered alongside symptoms, history, and other test results.³

What can cause elevated CRP?

Many conditions can raise CRP levels, including bacterial or viral infections, inflammatory conditions (rheumatoid arthritis, lupus, inflammatory bowel disease), recent surgery or tissue injury, obesity, and smoking. CRP can also be mildly elevated without any identifiable cause in some people.

Limitations of the CRP test

CRP is a sensitive but non-specific marker — it can be elevated by many different conditions and doesn't tell you the cause of inflammation on its own. It's most useful as part of a broader workup alongside symptoms, history, physical exam, and other labs like CBC, ESR, or ferritin.

When to visit urgent care

If you have symptoms of infection or inflammation — such as fever, significant joint pain, severe fatigue, or persistent illness — urgent care can order a CRP test alongside other labs to help identify the cause. Many urgent care centers offer on-site bloodwork with results available same-day. Use Solv to find urgent care near you that offers lab testing.