C-reactive protein (CRP) is a substance your liver produces in response to inflammation. When your body is fighting an infection, dealing with tissue damage, or experiencing chronic inflammatory conditions, CRP levels in your blood rise, sometimes dramatically. Healthy people typically have very low amounts, below 0.8 to 1.0 milligrams per deciliter (mg/dL). Doctors use CRP as a general marker to detect and monitor inflammation, though it doesn’t pinpoint exactly where the inflammation is coming from.
How Your Body Makes CRP
CRP production starts with your immune system’s signaling molecules, called cytokines. When inflammation occurs anywhere in the body, immune cells release a cytokine called IL-6, which travels through the bloodstream to the liver. Once IL-6 reaches liver cells, it activates a chain of signals that ramp up CRP production. A second signaling molecule, IL-1β, amplifies this process exponentially when both are present at the same time. This is why CRP can spike so quickly during a serious infection: the two signals compound each other.
CRP levels can rise within hours of an inflammatory trigger and may increase a hundredfold or more during a severe bacterial infection. They also fall relatively quickly once the underlying problem resolves, which makes CRP useful for tracking whether a treatment is working.
What CRP Levels Mean
A standard CRP test measures the protein in your blood and reports results in mg/dL or mg/L (the units matter, so check which your lab uses). In healthy adults, CRP sits at or below 0.8 to 1.0 mg/dL. Any increase above that range signals inflammation somewhere in the body.
Mildly elevated CRP can reflect a wide range of conditions: a lingering viral infection, obesity, poor sleep, gum disease, or a flare of an autoimmune condition like rheumatoid arthritis or lupus. Moderately to sharply elevated levels often point to something more acute, such as a bacterial infection, a significant injury, or a post-surgical inflammatory response. The higher the number, the more intense the inflammation tends to be, but CRP alone can’t tell your doctor the cause. It’s almost always interpreted alongside other tests, imaging, and symptoms.
Standard CRP vs. High-Sensitivity CRP
There are two versions of the test, and they serve different purposes. A standard CRP test is designed to detect the kind of large spikes that happen with infections and active inflammatory diseases. It’s what your doctor might order if you have a fever of unknown origin or if they’re monitoring a condition like Crohn’s disease.
A high-sensitivity CRP test (hs-CRP) can detect much smaller increases in the protein. This precision matters for cardiovascular risk assessment, where the differences between low and elevated levels are subtle. The hs-CRP test is most useful for people at intermediate risk of heart disease, meaning those with roughly a 10% to 20% chance of a heart attack over the next decade. For someone already at very low or very high risk, the test is less likely to change the clinical picture.
CRP and Heart Disease Risk
Chronic, low-grade inflammation plays a role in the buildup of plaque inside artery walls. Over time, this narrows the blood vessels that supply the heart and can eventually lead to a heart attack. The hs-CRP test captures this kind of slow-burn inflammation that a standard CRP test would miss entirely.
Cardiovascular risk categories based on hs-CRP, measured in mg/L, break down as follows:
- Low risk: less than 1 mg/L
- Intermediate risk: 1 to 3 mg/L
- High risk: 3 mg/L or greater
These numbers aren’t used in isolation. They’re combined with cholesterol levels, blood pressure, family history, and other factors to build a fuller picture of your cardiovascular health. A high hs-CRP result doesn’t mean you’ll have a heart attack. It means inflammation is adding to your overall risk profile.
Common Causes of Elevated CRP
Because CRP responds to inflammation broadly, the list of things that can raise it is long. Infections are the most obvious trigger, from a urinary tract infection to pneumonia. Autoimmune diseases like lupus and rheumatoid arthritis cause persistent elevation that often tracks with flare-ups. Inflammatory bowel disease, including Crohn’s and ulcerative colitis, can push CRP up significantly during active episodes.
Less obvious contributors include excess body weight (fat tissue produces its own inflammatory signals), obstructive sleep apnea, smoking, and a sedentary lifestyle. Even chronic stress and poor diet can nudge CRP levels upward over time. This is one reason a single CRP reading without context isn’t very informative. Your doctor will often repeat the test or combine it with other markers to distinguish a temporary spike from a chronic pattern.
What Lowers CRP
Lifestyle changes can meaningfully reduce CRP, especially over the long term. A study tracking nearly 1,800 people with heart disease over about 10 years found that CRP fell most substantially in those who quit smoking, lost weight, or increased their physical activity. On average, the full group’s CRP dipped only slightly, but the people who made specific changes saw larger drops. This suggests that targeted behavior changes matter more than time alone.
Regular exercise is one of the most consistent CRP-lowering interventions studied. Weight loss reduces the inflammatory output of fat tissue directly. Quitting smoking removes a major source of ongoing vascular inflammation. Dietary patterns rich in vegetables, fruits, whole grains, and healthy fats (often described as a Mediterranean-style diet) are also associated with lower CRP, though the effect is harder to measure precisely because diets vary so much between individuals.
On the medication side, statins lower CRP by an average of about 0.65 mg/L, independent of their cholesterol-lowering effect. Omega-3 fatty acid supplements also produce a small but measurable reduction. Interestingly, some cholesterol-lowering drugs don’t lower CRP at all, and a couple of classes may raise it slightly, which reinforces the idea that CRP reduction is a separate mechanism from cholesterol management.
What a CRP Test Can and Can’t Tell You
CRP is a powerful screening tool precisely because it’s nonspecific. It picks up inflammation from virtually any source, making it useful as an early alert. If you feel fine but your CRP is elevated, it can prompt your doctor to look deeper for something that hasn’t caused symptoms yet. If you’re being treated for an infection or an autoimmune flare, falling CRP levels are a reliable sign that the treatment is working.
What CRP cannot do is diagnose a specific disease. A high reading could mean a dozen different things. It also fluctuates naturally. A single elevated result after a cold, a poor night of sleep, or an intense workout doesn’t necessarily signal a problem. Patterns over time, especially when paired with symptoms and other lab work, are far more meaningful than any one number.