C-Reactive Protein Test

What is the CRP test?

CRP or c-reactive proteins are one of acute phase reactant proteins, made by the liver in response to inflammation, infection, or tissue destruction in the body. CRP is also released by immune cells such as macrophages, lymphocytes, and many other tissues such as smooth muscle cells, epithelial cells, and adipocytes. They are principal components of the immune system and serve as an early marker of acute infection or inflammation in the body. A CRP test measures the amount of c – reactive proteins in the blood.

CRP and inflammation

CRP opsonizes or marks the pathogens and target cells and promotes phagocytosis. They also activate phagocytes and the compliments system (part of the immune system). The concentration of CRP greater than 10 mg/l indicates some pathology. Normally they are in trace amounts less than 1 mg/l. During an infection or inflammatory condition level increases within 4-8 hours and peaks at 350-400 mg/l within 48 hours. The level may increase to 4000 – fold in response to an acute infection.

What is the test result meaning

CRP is a non-specific indicator of inflammation and one of the most sensitive acute phase reactants. It can rise a thousand-fold in response to bacterial infection, fungal infection, and some viral infections and the rise can precede even before other signs and symptoms of the disease appear. The information is used in conjunction with other signs and symptoms of the disease for diagnosis.

In contrast to erythrocytes sedimentation rate (ESR) it provides a direct measurement of serum proteins that rises and falls rapidly in response to an acute Inflammation and/or tissue destruction.

Unlike ESR, CRP is unaffected by anemia, protein levels, red blood cell shape, or the patient’s age or sex. The test is done for early detection of bacterial infection and for following disease activity and therapy in a number of chronic diseases for example rheumatoid arthritis, autoimmune disorders, differential diagnosis of bacterial or viral infections, and pyelonephritis vs cystitis, suspected graft rejection, dementia, malignancy and organ failure, etc.

CRP and Heart Disease

CRP as a marker of inflammation was known for about 70 years but the role it plays in heart disease is recently discovered. The initial concept as an inert marker of inflammation is changed now.

Studies shows that CRP has a pro-inflammatory activity at a very low concentration of 3-10 μg /ml and increases atherogenesis.

It predicts dangerous atherosclerotic complications like myocardial infarction, stroke, and peripheral vascular disease. A positive correlation has been found between CRP levels and coronary thrombosis. Atherosclerosis, narrowing of arteries because of cholesterol deposition is an inflammatory disorder of the blood vessels. In patients having atherosclerosis inflammatory markers such as CRP is found raised in the blood. Individuals who have elevated levels of CRP have a cardiovascular risk 2-3 times more than individual who has lower levels. Inflammation is involved in all stages including early initiations and acute rupturing of plaques, which can result in a heart attack. CRP also has a role together with LDL cholesterol levels in the detection of high risks cases who yet do not have any problems to motivate them to healthy lifestyle. The prognosis of patients in the acute phase of cardiac injury is closely related to CRP levels. It also predicts recurrent heart attacks.

What is the difference between high sensitivity CRP test (hs-CPR test) and a standard CRP test

Recent awareness of CRP to cardiovascular disease has led to the development of higher sensitivity CRP assays. The high sensitivity CRP test (hs- CRP test) is a very sensitive test and measures a very small rise of CRP. The standard CRP test measures CRP in the range of 8-1000 mg/l or (0.8-100mg/dl). While the hs-CRP test can measure CRP in the range of 0.3-10 mg/l. The relationship of CRP level to cardiovascular risk is suggested as following

  • Less than 1 mg/l: desirable and reflect low cardiovascular risk
  • 1-3 mg/l: moderate risk
  • Greater than 3 mg/l: quite elevated risk

CRP, Diabetes and the Metabolic Syndrome

Increased CRP levels also predict the development of type 2 diabetes.

People who have CRP greater than 3 have 4-6 times more risk of getting diabetes than people who have lower CRP levels

Part of the link between heart disease and diabetes is because of inflammation and for many patients Inflammation, in turn, is the result of obesity particularly central obesity because fat cells produce messenger proteins that turn on the production of CRP itself. Metabolic syndrome is a condition that predisposes the patient to diabetes and heart Disease. The patient is said to have metabolic syndrome if he has at least three of the following five conditions. That is lower HDL, increase triglycerides, central obesity, increase blood sugar levels, and high blood pressure.

How CRP is measured

CRP test is measured by enzyme-linked immunosorbent assay (ELISA), immunoturbidimetry, or antibody-based nephelometric assays which are typically sensitive to concentrations of 5-20 mg/l. The hs-CRP test can measure CRP in the range of 0.3-10mg/l.

At what age CRP test should be done

Many studies suggest that baseline levels of CRP in healthy people are highly predictive of future risk of heart disease, stroke, peripheral vascular disease, and sudden cardiac death. CRP levels baseline levels should be ideally performed in the mid-30s while checking serum cholesterol. Elevated CRP predicts the risk of cardiovascular disease over the next 30-40 years. Both LDL cholesterol and CRP together predict the risk of heart disease and stroke. Patients who have Increased CRP and lower LDL have more risk than people who have low CRP and high LDL levels, so CRP is a greater predictor of heart diseases than LDL cholesterol. However, considering the cost of hs-CRP and the fact that it is also increased in so many other conditions, tests are performed only for high cardiovascular risk cases. Current analytical methods of measuring CRP provide high sensitivity and accuracy but they are suitable for use in the laboratory and are expensive. There is a growing interest to develop tests that are suitable for point-of-care conditions and available for everyone.

Conditions in which CRP levels increase

The same factors which increase risks of heart disease also increase CRP levels, such as obesity, increased blood sugar, high blood pressure, Smoking, increase alcohol consumption, and an inactive lifestyle. Using oral estrogen by postmenopausal women increases CRP and anti-estrogen medicines decrease CRP levels.

How to lower CRP levels

Factors that reduce cardiovascular risk are the same which lower CRP, for example, Low fat, low cholesterol or low glycemic diets, exercise, weight loss, blood pressure control, smoking cessation, and increasing physical activity. CRP is lower in thin and athletics. A possible direct anti-inflammatory activity induced by Omega-3 polyunsaturated fatty acids intake has been suggested. However, the modification of CRP levels induced by it is still controversial. Some multivitamins especially vitamins E and C seem to decrease CRP but the role is still not confirmed.

The reduction of plasma CRP may represent a new approach to reducing inflammatory states during atherosclerogenesis. Statins drugs are highly effective at reducing heart attack and stroke as well as reducing recurrent cardiovascular events. Studies show that statins reduce both CRP levels and CRP-mediated pro-inflammatory activities. They work primarily by lowering LDL-C. Currently, Statin therapy is given to those patients with known heart disease, those with elevated levels of LDL cholesterol (above160mg/dl), and to diabetic patients. In healthy patients with high CRP levels and low LDC-C, the effect of statin therapy is not yet proven.

Aug 3, 2022

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