Acute-phase protein (Acute Phase Reactants)

• Acute-phase proteins are raised in inflammatory conditions.
• When there is an increase in an acute phase protein called positive acute-phase protein.
  • In the case of a decrease in the acute phase protein, it is called negative phase protein.
• The acute phase proteins (positive) are proteins whose concentration increases in the plasma, and after the disease episode is over, it decreases and may become normal.

C-Reactive Protein (CRP)

Sample

1. The venous blood of the patient is needed to prepare the serum.
2. A fasting sample is preferred.
3. A random sample can be taken.
4. Analyze the fresh sample.
   1. Or can store at 4 °C for <72 hours.
   2. At -20 °C for six months.

Indications for C-Reactive Protein (CRP)

1. Advised in bacterial infection.
2. It is advised in rheumatic fever.
3. It is advised in rheumatoid arthritis.
4. It may be advised after the surgery.
5. This is done in inflammatory diseases like acute rheumatic fever, rheumatoid arthritis, and bacterial infection.
6. It will help in the diagnosis of coronary artery disease.
7. This test can be done to diagnose bacterial endocarditis.
8. To diagnose appendicitis.
9. To diagnose active collagen vascular diseases.

Precautions for C-Reactive Protein (CRP)

1. This may be raised in cigarette smoking.
2. Avoid hemolysed and lipemic samples.
3. Raised values are seen in hypertension, diabetes mellitus, metabolic syndrome, gingivitis, and bronchitis.
4. Decreased values have seen weight loss, moderate consumption of alcohol, and exercise.
5. Estrogens and progesterone increase the C-Reactive Protein (CRP).
6. Niacin, statin, and fibrates decrease the C-Reactive Protein (CRP).
7. Keep in mind that:
   1. Cigarette smoking may increase the level.
   2. Estrogen and progesterone may increase the level.
   3. Niacin and statin may decrease the value.
   4. There may be an increased level of CRP in hypertension, diabetes mellitus, and metabolic syndrome.
8. Avoid lipemic or hemolyzed samples.

Pathophysiology of C-Reactive Protein (CRP)

Definition of C-Reactive Protein (CRP):

1. CRP is produced in the liver, and its name is derived from its reaction with streptococcal capsular polysaccharides.
2. CRP level supporting the diagnosis of bacterial endocarditis, appendicitis, and active collagen diseases was >10 mg/L.

3. There are changes in the plasma protein in response to:
   1. Acute illness.
   2. Trauma.
   3. Necrosis.
   4. Infarction.
   5. Burns.
   6. Chemical injury.
   7. Malignant tumors.
4. The acute reaction proteins  pattern is also called:
   1. Acute inflammatory response pattern.
   2. Acute stress pattern.
   3. Acute-phase protein pattern.

CRP (C-reactive protein)

1. History of CRP:
   1. In 1930 Tillet and Francis found substance in the sera of acutely ill patients.
   2. CRP  was given its name in 1941 because it is a protein.
   3. This substance binds the C-polysaccharides cell wall of Strept. pneumomiae.
   4. This leads to the agglutination of the bacteria.
   5. In 1940, this substance was shown to be a protein called C-reactive protein (CRP).
   6. Its detection limit for infection and autoimmune diseases was 3 to 8 mg/L.
      1. CRP molecular weight is ∼115 kDa.
      2. It is synthesized in the liver and has little or no carbohydrates.
2. Mechanism of action:
   1. It binds the C-polysaccharide of streptococcus pneumoniae and agglutinates the bacteria.
   2. This complex CRP is a potent opsonin for monocytes, leading to phagocytosis and activating the complement system.
   3. It activates the classical complement pathway.
   4. It binds to polysaccharides present in many bacteria, fungi, protozoal parasites, and histones.
   5. Its production is under the control of IL1 and IL-6.

3. The C-reactive protein name is derived from its reaction with streptococcal capsular (C) polysaccharides.
   1. CRP is the fastest responding acute-phase protein, as it increases 100 folds time with infection.
   2. So this is the most sensitive indicator.
   3. This increases in many diseases, so this has no specificity.
4. This is a nonspecific acute-phase protein with gamma mobility and is very helpful in monitoring inflammation.
   1. C-reactive protein on serum electrophoresis is found in the gamma region.

3. CRP is synthesized in the liver, and its synthesis is initiated by antigen complexes.
   1. Its production is controlled by interleukin-6.
4. CRP forms complex on the surface of bacteria (E.coli, S.pneumoniae), fungi, and other microorganisms.
   1. CRP binds to polysaccharides present in many bacteria, fungi, protozoal parasites, and histones.
5. It is found in the Gamma-region band on serum electrophoresis.

6. CRP is absent from a healthy person.
7. CRP  increased after any injury (trauma, bacterial infection, surgery, neoplasm, and inflammation) to 100 times.
   1. This is a nonspecific acute-phase protein.
   2. CRP starts rising after 4 to 6 hours of the infection, while other proteins rise after 12 to 36 hours of the initiating cause.
   3. CRP is functionally analogous to IgG, except it is not antigen-specific.
   4. This protein is synthesized in the liver and released into blood circulation after tissue injury in a few hours.
      1. The synthesis of the CRP is initiated by:
         1. Antigen immune complexes.
         2. Bacterial infection.
         3. Fungal infection.
         4. Trauma or tissue injury.

High-sensitivity CRP (hs-CRP):

1. hs-CRP is produced in the liver and is an acute phase reactant.
   1. It is induced by the release of interleukin 1 and 6; these interleukins reflect systemic inflammation activation.
2. It detects the lower level of CRP, which is important to finding the risk of cardiac events.
3. The sensitivity is 0.01 mg/dL.
4. In the case of raised hs-CRP, follow-up serial measurements are needed.
5. hs-CRP is useful for the risk of developing acute myocardial infarction with a history of acute coronary syndrome.
6. Value ≥1.0 mg/L indicates subclinical infection/inflammation; the test must be repeated in 3 to 4 weeks.
7. Coronary risk grades:

hs-CRP level	Degree of risk for cardiovascular diseases
<1.0 mg/L	Low risk
1.0 to 3.0 mg/L	Average risk
>3.0 mg/L	High risk Risk also increases for peripheral vascular disease. Risk increases for stroke

8. It is the first acute phase protein raised in inflammatory diseases, and its level increases tremendously.
   1. It is raised in acute and chronic inflammation.
9. This promotes the binding of Complements and helps in phagocytosis.

10. Its formation is initiated by the antigen-antibody immune complex.

11. This can induce the production of cytokines.
12. This can cause inhibition of chemotaxis and modulation of the WBC function.
13. The normal CRP level is <2 to 3 mg/L.
    1. The markedly raised level of >10 mg/L indicates an active inflammatory condition like collagen disease and infection.
    2. Its level does not rise consistently in the virus infection.

CRP vs. ESR:

1. More sensitive and rapidly responding than the ESR.
2. Other physiologic factors influence ESR, but CRP does not.
3. CRP tends to increase before the increase in ESR and the rise in antibodies titer.
4. CRP shows an earlier and more rapid increase in the acute inflammatory process than ESR.
5. In recovery, it becomes normal before the ESR.
6. It disappears when the disease is treated with cortisone or salicylates.
   1. This is useful for assessing the risk of myocardial infarction in patients with acute coronary signs and symptoms.

Parameters	CRP	ESR
Normal level	<1.0 mg/L	Men = 0 to 5  women = 5 to 15 mm/Hour
Sensitivity of the test	More sensitive	Less sensitive
Pathophysiology (Etiology)	Dead and dying tissue release chemical factors, which stimulate the liver to  produce CRP (IL1 and IL6)	Fibrinogen level goes up in the serum, which causes RBCs to clump
Rise of the test	Earlier increase	Late increase
Influence of other physiological factors	Not affect	Affected
Relation to antibody titer	Increase before antibodies	No relation to antibody
In acute inflammation	Early increase	Late increase
In recovery stage	Becomes normal early	Becomes normal late
AMI	Best indicator	No relation
Anginal attack	Normal	No relation
After the surgery	Good relation with recovery	No relation
Bacterial meningitis	The normal level excludes meningitis	No relation

C-Reactive protein role in various diseases:

CRP may be an indicator of various diseases like:

1. Tissue injury or necrosis of the tissues.
2. Various infections.
3. Monitoring course and effect of therapy.

In myocardial infarction (AMI):

1. CRP is raised, and it correlates with CK-MB isoenzyme in AMI.
2. Its peak level occurs 1 to 3 days later than CK-MB.
3. hs-CRP values >10 mg/L within 6 to 24 hours after the symptom onset indicates an increased risk for a recurrent cardiac event within 30 days to 1 year.
4. In unstable angina, hs-CRP values >10 mg/L will predict a higher chance of myocardial infarction/death compared to the group of patients with hs-CRP <10 mg/L.
5. CRP may remain increased in AMI for at least three months.
6. If the level persists, being raised indicates ongoing damage to myocardial tissue.
7. The baseline level is a good marker for future cardiovascular disease.
   1. CRP is a strong predictor of cardiovascular diseases than the low-density-lipoprotein (LDL) and cholesterol.
   2. CRP is a good marker for assessing the likelihood of recurrent myocardial infarction, restenosis, or death in patients with stable coronary disease.
   3. Its raised level is also reported as a risk factor for the development of hypertension.
8. Its level is normal in the case of angina.

In Pancreatitis:

1. A level of 150 mg/L distinguishes mild from severe acute pancreatitis.

Rejection phenomenon:

1. It helps rejection of kidney or bone marrow transplants but is not helpful in heart transplants.

Malignant tumors:

1. In 1/3 of the cases, CRP is >10 mg/L in malignant tumors of the breast, lungs, and GI tract.

After surgery:

1. It may be advised after the surgery when its level increases in 4 to 6 hours.
2. The peak level reaches 48 to 72 hours.
3. It starts going down after a 3rd postoperative day.
4. It returns to normal in 5 to 7 days.
5. Failure to return to a normal level raised level which indicates a complication of infection or pulmonary infarction.
   1. In that cases, advise CBC, ESR, temperature check, and pulse rate.

Meningitis:

1. It helps in the differential diagnosis of bacterial or viral meningitis.
2. In viral meningitis, it will not be raised.
3. The normal value excludes bacterial meningitis.

In burns,

1. The level may exceed 1000 mg/L.

CRP level is useful in:

1. Clinical evaluation of SLE, Leukaemia, Blast crisis, and ulcerative colitis.
2. There is a good correlation with ESR, but CRP appears and disappears earlier than changes in ESR.
3. The level of CRP increases dramatically than other Acute-phase proteins. So CRP is more useful as acute-phase proteins.
4. The quantitative test is more useful than a qualitative test.

Jones criteria for the diagnosis of Rheumatic fever:

Manifestations	Signs and symptoms
Major	Polyarthritis, carditis, subcutaneous nodule, chorea, Erythema marginatum
Minor	Fever and arthralgia
Minor	Raised CRP, raised ESR, evidence of group A streptococcal infection, and prolonged PR interval on ECG

Serology of CRP:

1. CRP appears 24 to 48 hours after the onset of infection.
2. The peak level reaches 72 hours.
3. It disappears from circulation after seven days.

4. Based on CRP level, there  are the following categories:
   1. Normal level = <3 mg/L.
   2. High level CRP = >10 mg/L (active inflammation).
   3. Low level  CRP =  3 to 10 mg/L. (Cellular stress).

Normal C-Reactive Protein (CRP)

• <1.0 mg/dL
• Source 2
  • <1.0 mg/dL or <10.0 mg/L
  • Cardiac disease risk:
    • Low = <1.0 mg/dL
    • Average = 1.0 to 3.0 mg/dL
    • High = >3.0 mg/dL
• Source 4
  • CRP = <0.8 mg/dL (<8.0 mg/L) (by nephelometry)
  • CRP reportable value = 0.3 to 20 mg/dL
  • hs-CRP = 0.020 to 0.800 mg/dL  (o.2 to 8.0 mg/L) (by immunoassay)
• Value ≥1.0 mg/L represents subclinical infection/inflammation and should be repeated in 3 to 4 weeks.

The raised level is seen in:

1. Soft tissue Trauma.
2. Infection.
3. Tissue necrosis.
4. Patients with Rheumatoid arthritis.
5. In Rheumatic fever.
6. Patients with systemic lupus erythematosus.
7. Patient with pneumonia.
8. Patient with malignancies.
9. In pregnant ladies.
10. Pulmonary tuberculosis.
11. Urinary tract infection.
12. Myocardial infarction.
13. Vasculitis syndrome.
14. Bacterial meningitis.

Decreased CRP level is seen in:

1. This may be seen in the moderate use of alcohol.
2. In weight loss.
3. Strenuous exercise.
4. Medicine like Niacin, and a statin.
5. Pregnancy.
6. Angina.
7. Seizures.
8. Asthma.
9. Common cold.
10. Rejection of heart transplant.
11. Autoimmune diseases like SLE, scleroderma, dermatomyositis, and mixed connective tissue disease.

The panic value of hs-CRP

• >3.5 mg/L
• In acute inflammation = >10.0 mg/L

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