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CRP test, i.e. Acute phase protein helps to judge whether your body is undergoing microbial inflammation, tissue damage, developing cancer, or an autoimmune process. Who should perform a CRP protein test? What is the CRP standard and how to interpret the result?

CRPis a glycoprotein composed of 5 identical subunits (pentamer) with a mass of 23 kDa. It belongs to the so-called acute phase proteins and is part of the non-specific immune response. CRP is produced mainly by the liver under the influence of pro-inflammatory cytokines. In addition, its smaller amounts of CRP can be produced by nerve cells, monocytes, lymphocytes and atherosclerotic plaque.

CRP protein was discovered by Tillett and Francis in 1930 and was first isolated from the serum of a patient with acute inflammation caused by the bacteriumStreptococcus pneumoniae .

What is CRP?

The CRP protein is a nonspecificmarker of inflammationand cannot locate the source of inflammation or determine its cause. Additional imaging and laboratory tests should be performed in order to determine the source and cause of inflammation.

Factors influencing the concentration of CRP protein

The concentration of CRP protein is influenced by various factors:

  • age
  • race
  • gender
  • season
  • physical activity

In addition, some drugs such as NSAIDs, statins, and fibrates can falsely lower CRP levels because these drugs reduce the inflammatory response in the body. In addition, magnesium supplementation may falsely lower CRP protein levels.

What is the CRP test and what are the standards?

The CRP protein determination is performed from venous blood taken from the elbow bend. You don't need to fast. The price of a test in a private laboratory ranges from PLN 10 to PLN 25.

Laboratory standard for protein may vary from lab to lab.

It is usually assumed thatCRP protein values ​​in he althy people should be below 10 mg / l .

On the other hand, values ​​above 10 mg / l may indicate ongoing inflammation in the body.

In diagnostic laboratories, CRP protein is determined using immunoturbidimetric, immunonephelometric or enzyme immunoassay methods(e.g. ELISA).

In the diagnosis of CRP protein, conventional methods are used, the detection threshold of which is 5-10 mg / l. However, more and more commonly used are highly sensitive methods with a detection threshold of about 0.01 mg / l.

They allow for the assessment of very low concentrations of CRP protein (the so-calledhighly sensitive CRP protein or hs-CRP ). The same chemical is tested in both cases, but the hs-CRP test is much more sensitive and can be used to assess the risk of cardiovascular disease.

Types of CRP proteins

The CRP protein secreted by the liver consists of five identical subunits arranged in a ring. This biochemical form of the CRP protein is called the pentameric isoform of CRP (pCRP) and is very soluble in blood. The pCRP protein has primarily anti-inflammatory properties and is mainly involved in the inflammation recovery phase.

When the pCRP protein interacts with damaged cells or microorganisms, its protein subunits irreversibly break down, giving rise to the momomeric isoform of the CRP protein (mCRP). Unlike the pCRP isoform, the mCRP protein is pro-inflammatory, and its insolubility in the blood causes it to remain at the site of inflammation.

Interpretation of the CRP result

The highest concentration of CRP protein(even above 500 mg / l) is observedduring infections with gram-negative bacteria .

Infections with gram-positive bacteria and parasites result in a less rapid increase in CRP protein (approximately 100 mg / L).

The CRP protein has the least responsiveness to viral infections (increase to about 50 mg / l).

In order to differentiate bacterial from viral infections with a similar clinical course, procalcitonin levels are frequently ordered. The concentration of procalcitonin increases significantly during bacterial infection, while its concentration increases slightly in the case of viral infection.

What does elevated CRP mean?

CRP protein is a non-specific marker of ongoing inflammation, infection, tissue damage and necrosis.

Very high blood levels of CRP should cause concern for the patient as it may be caused by:

  • bacterial infections, e.g. streptococci
  • fungal infections, e.g. candidiasis
  • parasitic infections, e.g. human roundworm
  • connective tissue diseases, e.g. systemic lupus erythematosus, rheumatoid arthritis
  • inflammation of the intestines, e.g. Crohn's disease
  • cancer e.g. colorectal cancer
  • acute pancreatitis
  • a heart attackheart muscle
  • convalescence after surgery

High blood levels of CRP may be caused by:

  • viral infections e.g. hepatitis B virus
  • old age
  • smoking
  • overweight or obese
  • diabetic
  • hypertension
  • using hormone replacement therapy
  • dental diseases
  • gum disease
  • pregnant

CRP testing and cardiovascular disease

CRP testingis also used in assessing the risk of cardiovascular disease. In this case, thehighly sensitive protein CRPis marked and the interpretation of the test result is determined as follows:

  • hsCRP less than 1 mg / l - low cardiovascular risk
  • hsCRP 1-3 mg / l - moderate cardiovascular risk
  • hsCRP over 3 mg / l - high cardiovascular risk

CRP study - the role of CRP in the body

CRP is produced during inflammation, mainly by interleukin 6 (IL-6), but also to a lesser extent by interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α).

When the concentration of IL-6 increases during acute inflammation, the liver starts producing the CRP protein, the concentration of which in the blood rises sharply (up to 1000-fold).

CRP levels begin to rise 4 to 6 hours after onset of inflammation and peak at approximately 1 to 2 days.

The CRP protein plays a role in recognizing microbes and damaged cells. By binding to antigens on the surface of microorganisms, it facilitates their recognition and removal by the immune system.

To this end, it has the ability to activate the complement system and phagocytic cells (neutrophils and macrophages) via Fc receptors. In addition, it stimulates further secretion of IL-6, IL-1 β and TNF-α.

It also turns out that the CRP protein, in addition to the aforementioned pro-inflammatory properties, also has anti-inflammatory properties, as it stimulates the release of anti-inflammatory cytokines such as interleukin 10 (IL-10). This usually happens when CRP is involved in wound healing, tissue repair, and the removal of damaged cells.

CRP - indications for the test

The indication for aCRP testin the laboratory is suspected acute or chronic inflammation and tissue damage. Therefore, the CRP protein test is ordered in the course of:

  • bacterial, viral, fungal or parasitic infections
  • autoimmune diseases
  • enteritis
  • acute pancreatitis
  • myocardial infarction
  • in the postoperative period
  • cancer
  • fever of unknown cause

CRP protein may also be elevated in the course of:

  • diabetes
  • obesity
  • sleep disorders
  • mental disorders
  • during chronic stress

Currently, however, its clinical significance in these diseases has not been established and requires further research.

The determination of CRP protein is also useful in monitoring the dynamics of the inflammatory process during treatment, e.g. in rheumatic diseases.

When inflammation wears off, CRP levels drop in just 24 hours.

The rate of decline in CRP protein makes it a very good indicator of postoperative infections, acute infections in newborns and children, and an early indicator of transplant rejection.

About the authorKarolina Karabin, MD, PhD, molecular biologist, laboratory diagnostician, Cambridge Diagnostics Polska A biologist by profession, specializing in microbiology, and a laboratory diagnostician with over 10 years of experience in laboratory work. A graduate of the College of Molecular Medicine and a member of the Polish Society of Human Genetics. Head of research grants at the Laboratory of Molecular Diagnostics at the Department of Hematology, Oncology and Internal Diseases of the Medical University of Warsaw. She defended the title of doctor of medical sciences in the field of medical biology at the 1st Faculty of Medicine of the Medical University of Warsaw. Author of many scientific and popular science works in the field of laboratory diagnostics, molecular biology and nutrition. On a daily basis, as a specialist in the field of laboratory diagnostics, he runs the content department at Cambridge Diagnostics Polska and cooperates with a team of nutritionists at the CD Dietary Clinic. He shares his practical knowledge on diagnostics and diet therapy of diseases with specialists at conferences, training sessions, and in magazines and websites. She is particularly interested in the influence of modern lifestyle on molecular processes in the body.

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