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What is C-reactive protein?

CRP is an acute phase protein synthesized by liver cells when the body is subjected to inflammatory stimuli such as microbial invasion or tissue damage. Among them, the concentration of CRP in the serum of healthy people is very low (<5mg / L), and its concentration is significantly increased during bacterial infection or tissue damage, so it is considered to be the most valuable.
       Note: Acute phase reactions include changes in certain serum protein concentrations during infection, inflammation, and trauma. These proteins include serum amyloid A, fibrinogen, haptoglobin, α1 acid glycoprotein, and copper blue in addition to CRP. Protein, α1 antitrypsin, etc.
Normal reference value
What is C-reactive protein?(图1)
What does it reflect
Screening for organic diseases, acute or chronic inflammation such as with bacterial infection, autoimmune or immune complex disease, tissue necrosis and malignancy
1 Diagnosis and identification of infection
◆ CRP begins to increase 6-8 hours after the occurrence of bacterial infection, and reaches a peak in 24-48 hours. After the infection is eliminated, its content drops sharply and can return to normal within one week.
CRP did not increase significantly during virus infection.
◆ Gram-negative infection: The highest level of CRP can occur, sometimes as high as 500 mg / L.
◆ Gram-positive bacterial infections and parasitic infections: usually cause moderate reactions, typically around 100 mg / L.
◆ Virus infection: the lightest reaction is caused, usually not more than 50mg / L, rarely more than 100mg / L.
◆ In the acute phase of bacterial infection, CRP was significantly increased and oligoadenosine synthase was normal.
◆ CRP levels are normal or slightly elevated during viral infections, and oligoadenosine synthase levels are elevated.
2 Predicting the risk of future myocardial infarction and stroke
◆ C-reactive protein is the strongest risk indicator for cardiovascular disease. C-reactive protein levels can predict the risk of myocardial infarction and stroke in the future. Comparison of people with C-reactive protein content> 2.1mg / L and those with <1mg / L:
The future risk of myocardial infarction is 2.9 times that of the latter;
The risk of ischemic stroke is 1.9 times that of the latter;
The risk of peripheral arterial vascular disease is 4.1 times that of the latter.
◆ Within a few hours after the onset of pain, CRP increased and reached a peak at 3 to 4 days. After CK-MB returned to normal, 7-10 days also returned to normal.
3 Autoimmune or immune complex disease
◆ Systemic lupus erythematosus, polymyositis, and systemic sclerosis have no significant changes in CRP, so they can be used to distinguish them from rheumatic diseases.
◆ If there is fever, it is a concurrent infection rather than a worsening of the disease.
4 Cancer
Elevated or increasing CRP indicates a poor prognosis and often prompts metastasis.
Colon cancer is the second most common cause of death. Studies have shown that those with the highest levels of C-reactive protein in their blood have twice the risk of developing colorectal cancer than those with the lowest levels of C-reactive protein.
5 Assess disease activity and efficacy monitoring
◆ CRP of 10 ~ 50mg / L indicates mild inflammation.
◆ CRP rising to 100mg / L indicates a more serious disease, and its severity requires intravenous injection when necessary.
◆ CRP> 100mg / L indicates serious disease process and often indicates the presence of bacterial infection.
6 Antibiotic treatment testing
A series of plasma CRP measurements can be used as therapeutic monitoring of the following conditions:
◆ Effective use of antibiotics for many infections.
◆ Determine the dosage of anti-inflammatory drugs according to the change of CRP level.
◆ When CRP drops to normal, interrupt antibiotic treatment.
◆ Guidelines for antibiotic treatment when microbiological diagnosis is lacking in high-risk groups.
7 surgery
◆ 24 to 72 hours after the operation, the CRP level in the blood increased significantly, and returned to normal around 5-7 days.
◆ Continuously high levels after a sudden rise usually indicate a combined infection.
◆ For patients undergoing major and major surgery, perform routine tests once before and 3-7 days after surgery.
◆ People who continue to have high levels of CRP 5-7 days after surgery should be suspected of co-infection and follow-up monitoring with treatment.
8 Internal medicine
◆ Pneumonia: CRP> 100mg / L, strongly suggesting bacterial infections, such as suppurative bronchitis or pneumonia; typical viral pneumonia does not exceed 50mg / L.
Cardiovascular disease: Within a few hours after the onset of pain, CRP increases, reaching a peak at 3-4 days, and also returns to normal at 7-10 days after CK-MB returns to normal.
◆ Metabolic syndrome: Metabolic syndrome is divided into groups according to CRP levels: low-risk group, <1mg / L medium-risk group, 1-3mg / L high-risk group,> 3mg / L
9 Obstetrics and Gynecology
◆ Pelvic inflammatory disease and uterine appendicitis, CRP value increased.
◆ Pelvic masses and uterine fibroids are usually negative.
◆ Diagnosis of premature rupture of fetal membranes. In the case of premature rupture of the membrane, if the mother's CRP exceeds 50 mg / L 6-19 h before delivery, it can be used as the standard for adenocarcinoma in situ (AIS); the CRP of AIS appearing on the first day after delivery will be higher than that during normal delivery 2 -3 times.
◆ Uncomplicated CT and NG infections do not cause CRP elevation. But diffusion into the pelvic cavity can cause an acute phase response.
10 Pediatrics
◆ Neonatal toxemia: CRP> 10mg / L before 3 days of birth indicates infection; if CRP does not exceed 10mg / L within 24 hours, there will be no neonatal infection.
◆ Pediatric fever: if the illness is more than 12 hours, CRP is significantly greater than 40mg / L, and the erythrocyte sedimentation rate (ESR) is significantly greater than 30mm / h. It should be paid attention to bacterial infection.
◆ Meningitis: CRP> 20mg / L indicates the possibility of bacterial infection;> 100mg / L has diagnostic value of bacterial infection. CRP in the nodule is 20-60mg / L. Successful treatment can reduce CRP to normal within one week.

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