Qualitative determination of C-Reactive Protein (CRP)
IVD
Store at 2-8ºC.
PRINCIPLE OF THE METHOD
The CRP-latex is a slide agglutination test for the qualitative and semiquantitative
detection of C-Reactive Protein (CRP) in human serum. Latex particles coated with
goat IgG anti-human CRP are agglutinated when mixed with samples containing
CRP.
CLINICAL SIGNIFICANCE
CRP is an acute-phase protein present in normal serum, which increases significantly
after most forms of tissue injuries, bacterial and virus infections, inflammation and
malignant neoplasia.
During tissue necrosis and inflammation resulting from microbial infections, the CRP
concentration can rise up to 300 mg/L in 12-24 hours.
PRECAUTIONS
Components from human origin have been tested and found to be negative for the
presence of HBsAg, HCV, and antibody to HIV (1/2). However handle cautiously as
potentially infectious.
CALIBRATION
The CRP-latex sensitivity is calibrated to the Reference Material ERMDA 474/IFCC.
STORAGE AND STABILITY
All the kit components are ready to use, and will remain stable until the expiration
date printed on the label, when stored tightly closed at 2-8ºC and contaminations
are prevented during their use. Do not freeze: frozen reagents could change the
functionality of the test.
Mix reagents gently before use. Reagents deterioration: Presence of particles and turbidity.
ADDITIONAL EQUIPMENT
- Mechanical rotator with adjustable speed at 80-100 r.p.m.
- Vortex mixer.
- Pippetes 50 µL.
SAMPLES
Fresh serum. Stable 7 days at 2-8ºC or 3 months at –20ºC.
Samples with presence of fibrin should be centrifuged before testing.
Do not use highly hemolysed or lipemic samples.
PROCEDURE
Qualitative method
Allow the reagents and samples to reach room temperature. The sensitivity of the
test may be reduced at low temperatures.
Place 50 µL of the sample (Note 1) and one drop of each Positive and Negative
controls into separate circles on the slide test.
Mix the CRP-latex reagent vigorously or on a vortex mixer before using and add
one drop (50 µL) next to the samples to be tested.
Mix the drops with a stirrer, spreading them over the entire surface of the circle.
Use different stirrers for each sample.
Place the slide on a mechanical rotator at 80-100 r.p.m. for 2 minutes. False
positive results could appear if the test is read later than two minutes.
Semi-quantitative method
Make serial two fold dilutions of the sample en 9 g/L saline solution.
Proceed for each dilution as in the qualitative method.
READING AND INTERPRETATION
Examine macroscopically the presence or absence of visible agglutination immediately
after removing the slide from the rotator. The presence of agglutination indicates a
CRP concentration equal or greater than 6 mg/L (Note 2 and 3).
The titer, in semi-quantitative method, is defined as the highest dilution showing a
positive result.
CALCULATIONS
The approximate CRP concentration in the patient sample is calculated as follow:
6 x CRP Titer = mg/L
QUALITY CONTROL
Positive and Negative controls are recommended to monitor the performance of
the procedure, as well as a comparative pattern for a better result interpretation.
All result different from the negative control result, will be considered as a positive.
REFERENCE VALUES
Up to 6 mg/L. Each laboratory should establish its own reference range.
PERFORMANCE CHARACTERISTICS
1. Analytical sensitivity: 6 (5-10) mg/L, under the described assay conditions.
2. Prozone effect: No prozone effect was detected up to 1600 mg/L (Note 1).
3. Diagnostic sensitivity: 95,6%.
4. Diagnostic specificity: 96,2%.
INTERFERENCES
Bilirubin (20 mg/dL), hemoglobin (10 g/L), and lipids (10 g/L), do not interfere. Rheumatoid
factors (100 IU/mL), interfere. Other substances may interfere7.
NOTES
1. High CRP concentration samples may give negative results (prozone effect).
Re-test the sample again using a drop of 20 µL.
2. The strength of agglutination is not indicative of the CRP concentration in the samples
tested.
3. Clinical diagnosis should not be made on findings of a single test result, but should
integrate both clinical and laboratory data.
