C-Reactive Protein (CRP)
Also known as: hs-CRP (high-sensitivity), hsCRP, Cardiac CRP
CRP is a protein released by the liver in response to inflammation. Depending on which assay is ordered, it serves as either a sensitive general inflammation marker (standard CRP) or a cardiovascular risk predictor (high-sensitivity CRP, hs-CRP).
Venous blood (serum separator tube)
4–6 hours
Not required
Inflammation & Infection
Reference Ranges
| Measurement | Reference Range | Unit |
|---|---|---|
| Standard CRP (normal) | ≤ 10 | mg/L |
| hs-CRP (low CV risk) | ≤ 1 | mg/L |
| hs-CRP (moderate CV risk) | 1 – 3 | mg/L |
| hs-CRP (high CV risk) | ≥ 3 | mg/L |
Reference ranges are typical adult values. Your laboratory may use slightly different intervals — always use your lab's reported reference.
What This Test Measures
CRP is an acute-phase reactant synthesised by the liver within 6–12 hours of an inflammatory stimulus. Standard CRP is useful for detecting and monitoring active infection, autoimmune flares, and post-surgical recovery. High-sensitivity CRP (hs-CRP) uses a more sensitive assay that detects chronic low-grade vascular inflammation linked to cardiovascular risk, independent of cholesterol levels.
When Is This Test Ordered?
- Detecting or confirming acute infection or inflammation
- Monitoring rheumatoid arthritis, lupus, or IBD disease activity
- Cardiovascular risk stratification (hs-CRP) in intermediate-risk patients
- Guiding antibiotic therapy duration
- Post-operative infection surveillance
When Results Are High
Standard CRP above 100 mg/L strongly suggests bacterial infection. Levels 10–100 mg/L occur with moderate infection, autoimmune disease, or major surgery. hs-CRP above 3.0 mg/L doubles cardiovascular event risk compared to hs-CRP below 1.0 mg/L (after ruling out acute infection).
When Results Are Low
CRP below the detection limit is simply reassuring — there is no clinical significance to a 'very low' value.
CRP vs. ESR: which inflammation marker should you use?
| Feature | CRP | ESR |
|---|---|---|
| Rises after stimulus | 6–12 hours | 24–48 hours |
| Falls after resolution | 24–48 hours | Days–weeks |
| Best for | Acute infection, treatment monitoring | Chronic disease activity, myeloma |
| Affected by anaemia | No | Yes (falsely elevated) |
| Affected by pregnancy | Mild rise | Significant rise |
Factors That Can Affect Your Result
- Any acute infection or injury can raise CRP 1000-fold within 24–48 hours
- Obesity chronically raises hs-CRP by 2–3 mg/L independently of other risk factors
- Statins reduce hs-CRP by 15–25% beyond their LDL-lowering effect
- NSAIDs and corticosteroids suppress CRP even during active disease
- Do not measure hs-CRP during acute illness — result will reflect infection, not baseline vascular risk
Tracking This Test Over Time
For cardiovascular risk assessment, measure hs-CRP twice (2 weeks apart) when well, and average the results. A persistently elevated hs-CRP (above 2 mg/L) is a validated indication for statin therapy in intermediate-risk patients with LDL already below target (JUPITER trial).
Track your CRP in LoomsRelated Tests
ESR
ESR measures how quickly red blood cells settle in a tube — inflammation makes them clump and fall faster. It is a non-specific but clinically useful marker for detecting and monitoring inflammatory conditions.
Ferritin
Ferritin is the body's primary iron storage protein and the most sensitive blood test for detecting iron deficiency — it falls before haemoglobin or serum iron does. But it is also an acute-phase reactant, which means inflammation can mask deficiency.
Lipid Panel
The lipid panel measures four fat-related molecules in the blood — total cholesterol, LDL, HDL, and triglycerides — and remains the cornerstone of cardiovascular risk assessment.
Medical disclaimer
This page is for educational purposes only and does not constitute medical advice. Reference ranges vary between laboratories, and results must be interpreted in the context of your symptoms, history, and other tests. Always discuss your results with your healthcare provider. Content reviewed by the Looms medical team, 2026-06-01.