C-Reactive Protein (CRP)

CRP (C-reactive protein) is one of the acute-phase proteins, like prealbumin and transferrin, which is produced in the liver. The greater the increase in CRP, the higher the inflammatory activity or the more inflamed tissue is present. A normal CRP value practically excludes a systemic bacterial infection. The CRP rise is approximately 6-12 hours after the onset of an acute inflammatory response. The maximum is to be expected after 48-72 hours, i.e. in the case of an acute infection, a clinical deterioration precedes the CRP rise.Since CRP has a very short half-life of only 24 hours, the course of an inflammation as well as the success of anti-inflammatory therapy measures can be monitored very well on the basis of CRP values. Due to the half-life of 24 hours, however, the CRP value can still be elevated when the clinical picture has already improved significantly.Due to the enormously wide reference range, a progression assessment of the CRP value provides more information than a single determination.

The procedure

Material required

  • Blood serum
  • Or LiH plasma, punctate

Standard values

Adults and children <0.5 mg/dl
Newborn up to 1.5 mg/dl

To use CRP as a risk factor, highsensitive-CRP (hs-CRP) is measured, which also captures the low range well (see below).

Indications

  • Differentiation of acute and chronic conditions (a significantly greater increase in CRP is observed in acute conditions); high sensitivity (percentage of diseased patients in whom the disease is detected by use of the test, i.e., a positive test result occurs) and specificity (probability that actually healthy individuals who do not suffer from the disease in question are also detected as healthy in the test) in the detection of acute and chronic disease
  • Differentiation between viral and bacterial infection not possible with certainty (in bacterial often stronger CRP increase than in viral infections).
  • Postoperative course – to detect postoperative complications (infections, necrosis):
    • Failure to drop 3rd – 4th postoperative day.
    • Postoperative complications: CRP increase > 50-150 mg/l
  • Necrotizing diseases
  • Rheumatologic diseases (the CRP rise is usually more sensitive than the leukocyte or ESR rise).
  • For therapy monitoring in inflammatory bowel disease (IBD; active Crohn’s disease is associated with an elevated CRP concentration, which correlates with disease activity); in ulcerative colitis, normal to only slightly elevated CRP concentrations are found (up to 5.0 mg/dl)

Interpretation

Interpretation of increased values

  • Atherosclerosis (arteriosclerosis, hardening of the arteries).
  • Acute bronchitis
  • Acute myocardial infarction (heart attack)
  • Acute pancreatitis (inflammation of the pancreas)
  • Leg vein thrombosis, deep
  • Chronic inflammatory bowel disease (IBD; see notes under indications).
  • Infectious diseases (for example, meningitis (meningitis), pneumonia (pneumonia), tuberculosis).
  • Malignancies (malignant tumors)
  • Mesenteric infarction (intestinal infarction)
  • Postoperative complications (see notes under indications).
  • Pyelonephritis (inflammation of the renal pelvis)
  • Peripheral arterial disease (pAVD; shop window disease) – the risk of AVC correlates with the levels of HbA1c and C-reactive protein. Patients who have high levels of both markers have the highest risk of AVC. The product of both parameters is highly significantly associated with progression (progression) of pAVD.
  • Rheumatic diseases (eg, in immune vasculitis (vascular inflammation due to a disorder of the immune system), sarcoidosis (inflammatory systemic disease affecting mainly the skin, lungs and lymph nodes)).
  • Sepsis (blood poisoning)

Other notes

  • A negative CRP on the second day of symptomatology is more likely to rule out severe bacterial infection.
  • In elderly patients, the acute-phase protein PCT is preferable to CRP in diagnosing bacterial infection.
  • Procalcitonin shows more rapid kinetics (speed of biochemical processes) than CRP.After the occurrence of bacterial, fungal and parasitic infection, it increases within a few hours (2-3 h) and reaches its maximum after 24 hours. Its biological half-life is 25-30 hours.In the case of active inflammation or bacterial infections (eg pneumonia / pneumonia) are usually higher CRP values (40-200 mg / L) to be detected.
  • The CRP value is considered a recognized indicator of atherosclerosis. This disease, in turn, increases the risk of myocardial infarction (heart attack) and apoplexy (stroke).
  • To use CRP as a risk factor, highsensitive-CRP (hs-CRP) is measured, which also captures the low range well.

Note: Detection of elevated inflammatory levels such as C-reactive protein (CRP) or procalcitonin (PCT) alone should not be an indication for antibiotic therapy (German Society of Infectious Diseases). Evaluation of highsensitive-CRP (hs-CRP) in relation to a future coronary event.

hs-CRP hs-CRP-related risk
<1.0 mg/l low risk
1 – 3 mg/l medium risk
> 3.0 mg/l high risk

The high-risk group has an increased relative risk of a future coronary event by a factor of 2.0 compared with the low-risk group.