CRP test

What’s measured

CRP levels in the blood

C-reactive protein (CRP) levels increase within a few hours after an infectious pathogen enters the body and reach their highest levels 24 to 48 hours after the onset of infection. .  A healthy adult usually has a CRP level of less than 3 mg/l, but can have higher levels, up to 10 mg/l. 
Basal CRP levels tend to be higher in women than in men, patients on hormone therapy, smokers and obese people, and they also rise with age. A CRP level higher than 10 mg/l may already indicate inflammation, but does not determine its cause or location (1).

In the blood, CRP increases in various infectious inflammations (acute, chronic), but also in non-infectious inflammation (e.g. rheumatoid arthritis, systemic vasculitis, atherosclerotic cardiovascular disease) and traumatic injury. The degree of elevation varies between pathological conditions.
In infections, there is a difference in the degree of increase in viral and bacterial infections. Viral infections are associated with only a slight rise in CRP values in the blood, usually not reaching more than 40-50 mg/l. In bacterial ones, CRP elevations are higher, usually in the hundreds of mg/l. This can help in the rapid differentiation of viral and bacterial infections.
Serum CRP values must always be considered in the context of the current clinical condition and other clinical information.

C-reactive protein (CRP) is a protein synthesized in the liver in response to an increase in plasma concentrations of IL-6 in particular, but also of other pro-inflammatory cytokines. It is one of the acute phase reactants and is part of the immune defence system. It activates the complement system, triggering opsonisation (labelling) and phagocytosis (engulfment) of pathogens and infected cells. Although it is a non-specific marker, in inflammation it is a better indicator than erythrocyte sedimentation rate or leukocyte count. A relatively small inflammatory reaction (bacterial, viral, non-infectious) is sufficient to stimulate its secretion. 

CRP is primarily used to quantify the degree of the inflammatory process and to monitor it in severe infectious and autoimmune diseases. It may also be useful in monitoring the response to antibiotic therapy in bacterial infections, as well as for the treatment of non-infectious inflammatory diseases.
Serum CRP values must always be considered in the context of the current clinical condition and other clinical information.

If you need to consult the results of the parameters, we recommend that you contact your GP or internist.

Instructions before collection

We do not recommend entry of patients/clients with clinical signs of disease (temperature, cough, signs of respiratory tract infection, etc.) to undergo this test.
We recommend hand disinfection prior to entry to the clinics/collection points.

It is advised to fast for a minimum of 8 hours by refraining from eating or drinking anything expect water. Faiing to fast before the test may affect result quality. If you are currently on medications, consult your healtcare provider to determine whether you should continue taking them prior to the test.

PREPARATION FOR BLOOD COLLECTION
The recommended time to collect blood is between 7 a.m. and 9 a.m., to obtain comparable results from different blood draws. To assess the numerical test result, so-called reference intervals are used, which are based on morning fasting collections and are used for population comparison. This time interval is also recommended in light of the biological cycles that naturally take place in the body.

GENERAL PRE-SAMPLING INSTRUCTIONS
It is necessary to come to the testing site earlier, so that you can rest in the waiting room for approximately 20 minutes to have a relatively relaxed body and mind.
It is necessary to arrive on an empty stomach for the collection itself, in the case of collections at a later time in the day, at least three hours on an empty stomach. At home, it is desirable to drink a sufficient amount of pure water (at least up to half a liter) - this is important for a successful blood collection. Mineral water, juice, coffee and tea are not recommended.
Herbs included in tea may contain substances affecting the blood count. Coffee and black tea increase gastric acid production and release insulin from the pancreas, thereby affecting glucose metabolism. Since everything in the body is interrelated, they can impact other tests. Another extreme is when your body is running out of fluids. In this case, the number of red blood cells, the level of protein and lipids bound to the protein increase and the level of urea in the blood can also increase. It is therefore advisable to drink pure water when you wake up.

Generally, it is recommended to:
• around 6 p.m. eat only light meals, do not eat fatty food (cheese, butter, cream, meat, smoked meat, bacon) and sweet meals,
• fast for 10-12 hours (Attention: it is not advisable to starve for more than 16 hours!), in the case of later collection (after 9:30 a.m.), a lighter breakfast is allowed, no later than 3 hours before collection,
• drink non-alcoholic beverages and drinks without sugar in the usual quantity, in the case of adult clients 24 hours before blood collection (Alcohol in the blood changes lipid levels, the level of glucose is reduced, uric acid levels increase and liver enzymes are released into the blood),
• take only prescribed medicines in the evening,
• avoid increased physical activity, and strength and endurance exercise the day before blood collection (Lipid, glucose, some enzyme levels in the blood and other parameters may change during physical activity. The recovery of normal values to maintain the accuracy of laboratory results may take a longer time, depending on the duration of the exercise, your physical fitness in general and other factors. We recommend maintaining normal daily physical activity such as light stretching, short cycling to work, gardening, etc.),
• avoid psychological stress, which raises blood glucose levels and causes the release of stress hormones in particular,
• avoid smoking for at least 6 hours prior to blood collection because it increases the level of carbonylhemoglobin produced by the reaction of the blood dye with carbon monoxide and alters the permeability and elasticity of the vessels, affecting the ratios of blood analytes,
• do not chew gum for at least 6 hours before blood collection, as this may affect glucose and enzyme levels,
• do not undergo stressful diagnostic or therapeutic interventions for at least 24 hours prior to blood collection.
If any of the tests you have selected require special preparation, you will be informed of the fact by email with the order and blood collection instructions attached. These specific instructions have priority over the general recommendations for preparation.

MEDICINES
It is recommended to have blood collected before the planned doses of medicines. If it is not possible to take the medicine later, you should inform the nurse during blood collection and specify what medication you have taken.
Take the medicines prescribed by your doctor in the morning or bring them with you to take them after blood collection (thyroid medicines, antihypertensive medicines, blood thinners, contraceptives, etc.) In the case of later collection (after 9:30 a.m.), you can take the prescribed medication in the morning.
Do not take iron, vitamin, nutritional supplements or other supplements, including homeopathics, for at least three (3) days prior to blood collection.

SPECIFIC SITUATIONS
In order to obtain the appropriate answers to your questions with regard to the laboratory tests, it is important to accurately notify the nurse at the healthcare provider about the following facts prior to your blood test:
• regularly used medicines and supplements (ideally come with a written list to the blood collection site),
infectious diseases you suffer from (e.g., HIV, hepatitis, mononucleosis...),
• contact with an infected person or presence in an infectious environment,
• if you have received an infusion within the last 5 days, specify into which limb,
• intramuscular injections within 3 days prior to the blood collection date,
• long-term immobilisation, lost ability to move,
• activities at higher altitudes,
• allergy to common band-aids,
• if you feel unwell when looking at blood or needles, please also notify our blood collection staff of the fact.

OTHER FACTORS
Please note that prolonged use of medication or other important factors may affect the values measured by the tests you have selected. For more information, please see the description of the specific test. To obtain objective test results, take the time to properly prepare for your blood collection.

Results

CRP values in the blood

High CRP values

Elevated values are observed several hours after the infectious pathogen has entered the body, with a maximum increase in concentration within 24 - 48 hours and may persist for a prolonged period of time. The CRP value and the dynamics of development depend on the type of infection.
In general, in viral infections, values rise only to a small extent, usually not exceeding 40-50 mg/l.  In bacterial infections, the values are higher.  
Elevated values are also present in various non-infectious inflammatory diseases (e.g. rheumatoid arthritis, non-specific inflammatory bowel disease, systemic vasculitis, etc.).

The rise in CRP concentration is low when the atherosclerotic process is active; therefore, a method accurate in the region of low concentrations, a method with higher sensitivity, must be used. In determining cardiovascular risk, the so-called hs- CRP, high-sensitivity CRP, is determined. 

Sources

1. Mouliou DS, Diseases. 2023 Sep 28;11(4):132.1
2. Zima T. a kol. Laboratorní diagnostika. Třetí, doplněné a přepracované vydání. Galen 2013, 1189 stran. ISBN 978-80-7492-074-5 (pdf)