What CRP level indicates infection?

CRP levels above 10 mg/L generally indicate active inflammation or infection. Bacterial infections typically cause CRP levels above 50–100 mg/L, often exceeding 200 mg/L in severe cases such as sepsis or pneumonia. Viral infections usually produce more modest elevations, typically below 50 mg/L. However, CRP is nonspecific — elevated levels can also be caused by autoimmune disease, tissue injury, or malignancy.

What is a dangerous CRP level?

CRP levels above 100 mg/L are considered markedly elevated and often indicate serious bacterial infection, severe tissue injury, or systemic vasculitis. Levels above 200–300 mg/L are frequently seen in sepsis, major burns, or severe bacterial infections. Any CRP above 100 mg/L warrants urgent clinical evaluation to identify the underlying cause.

What is the difference between CRP and hs-CRP?

Standard CRP and high-sensitivity CRP (hs-CRP) measure the same protein but differ in sensitivity. Standard CRP detects levels above 3–10 mg/L and is used to evaluate infection and acute inflammation. hs-CRP can detect much lower concentrations (below 1 mg/L) and is used specifically for cardiovascular risk stratification. hs-CRP categories for heart disease risk are: less than 1.0 mg/L (low risk), 1.0–3.0 mg/L (moderate risk), and greater than 3.0 mg/L (high risk).

What does a CRP of 50 mean?

A CRP of 50 mg/L indicates moderate inflammation. This level is commonly seen with active bacterial or viral infections, autoimmune disease flares (such as rheumatoid arthritis or inflammatory bowel disease), or after recent surgery or tissue injury. While not as alarming as levels above 100 mg/L, a CRP of 50 warrants clinical investigation to determine the cause.

How can I lower my CRP levels?

CRP levels decrease when the underlying cause of inflammation is treated. For chronic low-grade inflammation (mildly elevated hs-CRP), evidence-based strategies include regular aerobic exercise, weight loss, smoking cessation, and a Mediterranean-style diet rich in fruits, vegetables, and omega-3 fatty acids. Statins have been shown to reduce hs-CRP by 15–30% independent of their cholesterol-lowering effects. Addressing the underlying condition — whether infection, autoimmune disease, or lifestyle factors — is the most effective approach.

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CRP-Werte: C-reaktives Protein Normalbereich

A comprehensive reference on C-reactive protein (CRP) and high-sensitivity CRP (hs-CRP) — normal ranges, causes of elevation, cardiovascular risk categories, and clinical interpretation.

Normal CRP Range — Quick Reference

Standard CRP: <10 mg/L

hs-CRP (cardiovascular risk):
<1.0 mg/L = Low risk · 1.0–3.0 mg/L = Moderate risk · >3.0 mg/L = High risk

Values >10 mg/L indicate acute inflammation — not useful for CV risk assessment

What Is C-Reactive Protein (CRP)?

C-reactive protein (CRP) is an acute-phase reactant produced primarily by hepatocytes in response to interleukin-6 (IL-6) stimulation. It is one of the most widely used laboratory markers of systemic inflammation. CRP levels rise rapidly — often within 6–8 hours of an inflammatory stimulus — and can increase up to 1,000-fold during severe infections or tissue injury.¹

CRP was first identified in 1930 by Tillett and Francis, who discovered a substance in the serum of patients with pneumococcal pneumonia that reacted with the C-polysaccharide of Streptococcus pneumoniae. Since then, it has become a cornerstone of inflammatory assessment in clinical medicine, used to detect and monitor infections, autoimmune diseases, and post-surgical recovery.²

The development of high-sensitivity CRP (hs-CRP) assays expanded the clinical utility of CRP measurement. While standard CRP tests are designed to detect the marked elevations seen in acute illness, hs-CRP can detect the low-grade chronic inflammation associated with atherosclerosis and cardiovascular risk.³

CRP Normal Range

CRP reference ranges differ depending on whether a standard or high-sensitivity assay is used and the clinical context:

Standard CRP

CRP Level	Conventional (mg/L)	SI (mg/L)	Interpretation
Normal	<10	<10	No significant inflammation
Moderate elevation	10–100	10–100	Active inflammation — infection, autoimmune flare, tissue injury
Marked elevation	>100	>100	Severe infection (often bacterial), major tissue damage

hs-CRP (Cardiovascular Risk Stratification)

hs-CRP Level	mg/L	Cardiovascular Risk
Low risk	<1.0	Lower relative cardiovascular risk
Moderate risk	1.0–3.0	Average cardiovascular risk
High risk	>3.0	Higher relative cardiovascular risk
Acute inflammation	>10	Not useful for CV risk — investigate acute cause

CRP is measured in the same units (mg/L) in both conventional and SI systems. Some labs report CRP in mg/dL — multiply by 10 to convert to mg/L.

What Does a High CRP Level Mean?

Elevated CRP indicates systemic inflammation but is nonspecific — it does not identify the source. The degree of elevation can help narrow the differential:

Common Causes of Elevated CRP

Bacterial infection — CRP typically >100 mg/L in serious bacterial infections (pneumonia, pyelonephritis, sepsis). Bacterial infections generally produce higher CRP than viral infections.⁴
Viral infection — Usually CRP 10–50 mg/L, though severe viral illnesses (e.g., COVID-19 pneumonia) can cause marked elevation
Autoimmune disease — Rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease (especially Crohn's disease), and vasculitis
Tissue injury or surgery — CRP peaks 2–3 days post-operatively and should decline thereafter; persistent elevation suggests complications (e.g., infection)
Malignancy — Particularly lymphomas, renal cell carcinoma, and advanced solid tumors
Obesity — Chronic low-grade inflammation with mildly elevated hs-CRP (typically 3–10 mg/L), mediated by adipose tissue IL-6 production⁵
Smoking — Associated with mildly elevated hs-CRP levels

Symptoms Associated with High CRP

CRP itself does not cause symptoms. Clinical features depend on the underlying cause:

Fever, chills, malaise (infection)
Joint pain and swelling (autoimmune arthritis)
Abdominal pain, diarrhea (IBD flare)
Chest pain, dyspnea (pneumonia, PE)
Wound erythema or drainage (surgical site infection)

What Does a Low CRP Level Mean?

Low or undetectable CRP levels are generally not clinically significant and indicate an absence of systemic inflammation. There is no established pathologic condition associated with an abnormally low CRP.

In the context of hs-CRP cardiovascular risk stratification, a very low hs-CRP (<1.0 mg/L) is favorable and associated with a lower relative risk of future cardiovascular events.³

Some medications — particularly statins — can reduce hs-CRP levels by 15–30%, independent of their effects on LDL cholesterol. The JUPITER trial demonstrated that statin therapy reduced cardiovascular events in patients with elevated hs-CRP even with normal LDL cholesterol.⁶

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Klinische Praxistipps

🔑 Wichtige Hinweise

CRP >100 mg/L has roughly an 80–85% positive predictive value for bacterial infection, though autoimmune flares and major tissue injury can also reach this level.⁴
CRP has a short half-life (~19 hours), making it useful for monitoring treatment response. A declining CRP is reassuring; a rising or plateaued CRP after 3–4 days of antibiotics should prompt re-evaluation.
hs-CRP for cardiovascular risk should be measured twice (at least 2 weeks apart) in a non-inflamed state. A single hs-CRP >10 mg/L should be repeated after the acute process resolves.
CRP is minimally affected by anemia, polycythemia, red cell morphology, or protein levels — unlike ESR, which is affected by all of these.
Liver failure can blunt CRP production. In patients with severe hepatic dysfunction, a "normal" CRP does not exclude infection.
CRP does not cross the blood-brain barrier. It is not reliably elevated in isolated CNS infections (e.g., meningitis may show only modest CRP elevation early).
The 2019 ACC/AHA guidelines list hs-CRP ≥2.0 mg/L as a "risk-enhancing factor" that can guide statin initiation in borderline-risk patients (5–7.5% 10-year ASCVD risk).⁷

Test Methodology

CRP is measured by immunoassay (immunoturbidimetry or immunonephelometry). Standard CRP assays have a detection limit of approximately 3–8 mg/L. High-sensitivity assays detect concentrations as low as 0.1–0.3 mg/L, enabling cardiovascular risk stratification in the low mg/L range.

Specimen Requirements

CRP is measured on serum or plasma. No fasting is required. The sample is stable for several days refrigerated. Results are typically available within 1–2 hours in most hospital laboratories.

Referenzen

Burtis CA, Ashwood ER, Bruns DE, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.
Pepys MB, Hirschfield GM. C-reactive protein: a critical update. J Clin Invest. 2003;111(12):1805–1812. doi:10.1172/JCI200318921
Ridker PM. Clinical application of C-reactive protein for cardiovascular disease detection and prevention. Circulation. 2003;107(3):363–369. doi:10.1161/01.CIR.0000053730.47739.3C
Hofer N, Zacharias E, Müller W, Resch B. An update on the use of C-reactive protein in early-onset neonatal sepsis: current insights and new tasks. Neonatology. 2012;102(1):25–36. doi:10.1159/000336629
Visser M, Bouter LM, McQuillan GM, Wener MH, Harris TB. Elevated C-reactive protein levels in overweight and obese adults. JAMA. 1999;282(22):2131–2135. doi:10.1001/jama.282.22.2131
Ridker PM, Danielson E, Fonseca FAH, et al. Rosuvastatin to prevent vascular events in men and women with elevated C-reactive protein (JUPITER). N Engl J Med. 2008;359(21):2195–2207. doi:10.1056/NEJMoa0807646
Arnett DK, Blumenthal RS, Gerber B, et al. 2019 ACC/AHA guideline on the primary prevention of cardiovascular disease. Circulation. 2019;140(11):e596–e646. doi:10.1161/CIR.0000000000000678
Pearson TA, Mensah GA, Alexander RW, et al. Markers of inflammation and cardiovascular disease: application to clinical and public health practice (AHA/CDC scientific statement). Circulation. 2003;107(3):499–511. doi:10.1161/01.CIR.0000052939.59093.45

Referenzen zuletzt überprüft: Februar 2026