Rapid self-test for the detection of C-reactive protein (bacterial infection or inflammation) in blood
Intended Purpose
The CRP-Screen® is a manual semi-quantitative immunochromatographic screening test for the assessment of C-Reactive Protein (CRP) level in finger prick whole blood sample. It can be used at home by lay users for self-testing for the detection of bacterial infections or inflammatory disorders
General Points
The C-Reactive Protein (CRP) is a non-specific marker which is mainly produced by the liver and used to diagnose bacterial infectious disease and inflammatory disorders.
The CRP is a very sensitive and fast appearing indicator which could therefore be helpful for deciding an antibiotic treatment.
Depending on the CRP concentration, different lines will appear allowing the semi-quantitative interpretation of the test result.
In healthy patients, CRP concentration is lower than 8mg/L while the concentration level can go higher than 100mg/L in case of severe infection or during inflammatory process. Intermediate levels, within 8 and 100mg/L, are concomitant with more or less mildly viral or bacterial infections that can be easily overcome by appropriate treatment ordered by your doctor.
Test Procedure
Prepare everything properly before starting the testing procedure. Place the content of the box on a clean, dry and flat surface (e.g. table). Then perform the test as follows:
- Wash your hands thoroughly. Use soap and warm water. Dry your hand with clean towel.
- Prepare the test device and capillary pipette: Take them out from the protective pouch (tear at the notch) and place them in the reach of your hands (you will need them later). Discard the desiccant bag.
- Open the diluent dropper vial: Remove the screw cap of the vial and keep it nearby.
- Prepare the lancet. Hold the lancet without touching the trigger button. Unlock the cap twisting it off ¼ turn until you feel it separates from the lancet and then continue twisting it (2-3 rotations). Don’t pull just twist and discard the cap when finished. ①②
- Clean the end of the middle or ring finger with cotton damped with alcohol. Massage the chosen finger towards the tip for 10 to 15 seconds to enhance the blood flow.
- Prick the finger: put the lancet firmly against the side of the previously cleaned finger, and press the release trigger button.③ The lancet will automatically retract into the body of the device. Gently massage the finger to create a nice round blood droplet.④
- Collect the blood with the capillary pipette: Gently touch the blood droplet with the open end of the capillary pipette. It must be filled until the line indicated on the capillary pipette. Do not press the bulb, it fills by itself. Make another blood droplet if the line is not reached. As far as possible, avoid air bubbles. ⑤
- Place the collected blood sample into the previously opened diluent dropper vial by pressing the bulb of the pipette. Make sure that the complete volume of blood sample is added into the diluent dropper vial by pressing 2-3 times the bulb of the pipette and therefore rinsing the inner part of the pipette with diluent solution. Replace the screw cap on the diluent dropper vial and mix thoroughly. ⑥
- Break the tip of the dropper vial containing the diluted blood sample. Hold it vertically and slowly add exactly 4 drops in the sample well of the device with an interval of 2-3 seconds between each drop. ⑦&⑧
- Read the result after 5 minutes. Do not interpret after 10 minutes.
Results Interpretation
The results must be interpreted depending on the intensity colour of the 3 lines that could appear in the device window.
Analyze
Result
Summary
CRP level lower than 8 mg/L
CRP level in the range of 8 to 40mg/L
CRP level in the range of 40 to 100mg/L
CRP level over 100mg/L
Invalid result
Questions and Answers
How does CRP-Screen® work?
If present in the sample, CRP will interact with the anti CRP antibodies as well as with the CRP antigen placed in the test producing different lines allowing a semi-quantitative measurement of the CRP concentration in the blood sample (starting from 8 mg/L according to values determined against W.H.O.* reference). A control line capturing the reagent excess appears as a coloured line under the C mark of the cassette.
*World Health Organisation.
When should the test be performed?
CRP-Screen® test should be performed in the case of acute infection symptoms such as feverishness, fever, headaches or weakness. The test can be performed at any time of the day.
Can the result be incorrect?
The results are accurate as long as the instructions are carefully respected. Nevertheless, the result can be incorrect if CRP-Screen® test gets wet before test performing or if the quantity of diluted blood dispensed in the sample well is not sufficient.
The plastic pipette provided in the box allows making sure the collected blood volume is correct and is correctly diluted into the diluent dropper vial.
How to interpret the test if the colour and the intensity of the lines are different?
The colour intensity of the lines is important to interpret the test result. So please refer to the pictures and instructions in paragraph “Result interpretation”.
What is the line that appears under the mark C (Control) for?
When this line appears, it only means that the test has been performed well.
If I read the result after 10 minutes, will the result be reliable?
No. The test should be read 5 minutes after adding the diluant. The result is reliable up to 10 minutes.
What do I have to do if the result is positive?
If the result is positive when the CRP is higher than 8mg/L, please refer to the result interpretation and inform your doctor as soon as possible as an antibiotic treatment might be urgently needed.
What do I have to do if the result is negative?
If the result is negative when the CRP is lower than 8mg/L, it means that there is neither bacterial nor viral infection on the way. However, if the symptoms persist, it is recommended to consult your doctor.
Can drugs interfere on CRP level?
Few drugs as statin and fibrates reduce elevated CRP level whereas oral hormone therapy for menopause increases CRP level.
What is the accuracy of CRP-Screen® ?
The CRP-Screen® test is accurate and is used for more than 10 years by professionals in the field (hospitals, laboratories…). Evaluation reports show an overall agreement of 99.15% [95.07 – 100**] with reference methods. Although this test is reliable, false positive or false negative results can be obtained.
** CI 95%: 95% Confidence Interval.