Short answer
A CRP test measures C-reactive protein, a liver-made protein that rises when inflammation is present somewhere in the body. A high CRP result can show that inflammation is present, but it does not show the cause, location, or severity by itself.
High-sensitivity CRP, or hs-CRP, measures smaller CRP changes. It is usually discussed in a different context: cardiovascular risk. hs-CRP should be interpreted with cholesterol, blood pressure, diabetes, smoking, age, family history, symptoms, and the reason the test was ordered.
CRP versus hs-CRP
| Test | What it measures | Common use | Common trap |
|---|---|---|---|
| Standard CRP | Moderate to high levels of C-reactive protein. | May help detect or monitor inflammation from infection, inflammatory disease, surgery, injury, or treatment response. | Treating a high result as a diagnosis instead of a nonspecific inflammation signal. |
| High-sensitivity CRP | Very small changes in C-reactive protein. | May help refine heart-risk discussions when combined with other cardiovascular risk factors. | Using hs-CRP as a standalone heart-risk score or as proof of heart disease. |
Units matter. Some reports use milligrams per liter (mg/L); others use milligrams per deciliter (mg/dL). Do not compare two CRP results unless the units and test type are clear.
When standard CRP may be ordered
MedlinePlus says standard CRP may be used to help find or monitor inflammation. It may be ordered when symptoms suggest infection, sepsis, inflammatory bowel disease, rheumatoid arthritis, lupus, vasculitis, lung inflammation, or another inflammatory condition.
It can also be used to follow whether inflammation is improving after treatment or after a flare. A falling CRP can support the idea that inflammation is improving, but the trend still has to fit the clinical picture.
What high CRP can and cannot tell you
CRP can rise for many reasons, including infections, autoimmune disease, inflammatory bowel disease, asthma or lung inflammation, injury, recent surgery, obesity, smoking, environmental exposures, and other inflammatory stressors. Some medicines and supplements can also affect interpretation.
A high value does not tell you where the inflammation is or what caused it. A low value also does not perfectly rule out disease. CRP is one clue that usually needs symptoms, exam findings, timing, medication review, comparison with ESR or CBC, and sometimes repeat testing.
hs-CRP and heart risk
MedlinePlus notes that hs-CRP is used to estimate heart disease risk, and the American Heart Association describes it as one piece of information that may add clarity to a broader heart-health picture. CDC emphasizes that heart risk is shaped by conditions and behaviors such as high blood pressure, high cholesterol, diabetes, smoking, physical activity, weight, alcohol use, age, and family history.
The 2019 ACC/AHA primary prevention executive summary lists persistently elevated hs-CRP of 2.0 mg/L or higher as a risk-enhancing factor when measured. That does not mean hs-CRP causes heart disease or proves that heart disease is present. It means the result may influence a clinician-patient risk discussion, especially when the overall risk estimate is borderline or intermediate.
Result patterns to discuss
| Pattern | What it may mean | Useful follow-up question |
|---|---|---|
| High standard CRP | Inflammation is likely present, but the source is not identified by CRP alone. | What symptoms, exam findings, CBC, ESR, urine tests, cultures, imaging, or repeat labs fit this result? |
| Very high or rising CRP | May fit a significant inflammatory process, infection, injury, flare, or recent procedure depending on context. | Are there urgent symptoms or signs that should be evaluated now? |
| hs-CRP of 2.0 mg/L or higher | May act as a cardiovascular risk-enhancing factor if it is persistent and not explained by a temporary inflammatory trigger. | Should this be repeated when I am well, and how does it change my overall risk discussion? |
| Low CRP with symptoms | Does not always rule out inflammation or disease. | Are there other tests or clinical clues that matter more for my symptoms? |
Repeat testing, timing, and temporary elevations
CRP can change quickly. A result drawn during a cold, dental infection, injury, surgery recovery, inflammatory flare, recent vaccine reaction, intense training block, or other short-term stressor may not reflect a stable baseline.
For hs-CRP used in heart-risk discussions, ask whether the result should be repeated after acute illness has resolved. The key question is not just whether hs-CRP is elevated once; it is whether it is persistently elevated and still meaningful after obvious temporary causes have been considered.
Preparation, medicines, and supplements
CRP usually requires a blood sample from a vein. MedlinePlus advises telling the ordering clinician about supplements and medicines, including magnesium and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin, because some can affect results. Do not stop prescription medicines, aspirin, anti-inflammatory medicines, or supplements unless the clinician who ordered the test tells you to.
Questions to ask
- Was this a standard CRP or high-sensitivity CRP?
- What units does the lab report use, and what is this lab's reference range?
- Was I sick, injured, recently vaccinated, recovering from surgery, in an inflammatory flare, or under unusual physical stress near the test date?
- Should this be repeated after an acute illness or flare has resolved?
- Which symptoms, exam findings, medications, CBC, ESR, cultures, urine tests, imaging, or repeat labs help explain the result?
- If this was hs-CRP, how does it fit with cholesterol, blood pressure, diabetes, smoking, age, family history, and my overall cardiovascular risk estimate?
- Would the result change prevention decisions, or is it mainly background context?