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.
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
1. Allow the reagents and samples to reach room temperature. The
sensitivity of the test may be reduced at low temperatures.
2. Place 50 µL of the sample (Note 1) and one drop of each Positive
and Negative controls into separate circles on the slide test.
3. 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.
4. Mix the drops with a stirrer, spreading them over the entire surface
of the circle. Use different stirrers for each sample.
5. 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
1. Make serial two fold dilutions of the sample en 9 g/L saline solution.
2. 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.
