PRINCIPLE OF THE METHOD
The ASO-latex is a slide agglutination test for the qualitative and semiquantitative detection of anti-streptolysin O (ASO) in human serum.
Latex particles coated with streptolysin O (SLO) are agglutinated when
mixed with samples containing ASO.
CLINICAL SIGNIFICANCE
Streptolysin O is a toxic immunogenic exoenzyme produced by -
heamolitic Streptococci of groups A, C and G. Measuring the ASO
antibodies are useful for the diagnostic of rheumatoid fever, acute
glomerulonephritis and streptococcal infections. Rheumatic fever is an
inflammatory disease affecting connective tissue from several parts of
human body as (skin, heart, joints, etc…) and acute glomerulonephritis
is a renal infection that affects mainly to renal glommerulus.
CALIBRATION
The ASO-latex sensitivity is calibrated against the ASO International
Standard from NIBSC ASO.
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.
Do not use highly hemolized 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 and one drop of each Positive and
Negative controls into separate circles on the slide test.
3. Mix the ASO-latex reagent vigorously or on a vortex mixer before
using and add one drop (50 µL) next to the sample 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 in 9 g/L saline solution.
2. Proceed for each dilution as in the qualitative method.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 200 IU/mL(adults) and 100 IU/mL (children 5 years old)6
.
Each laboratory should establish its own reference range.
PERFORMANCE CHARACTERISTICS
1. Analytical sensitivity: 200 (± 50) IU/mL, under the described assay
conditions
2. Prozone effect: No prozone effect was detected up to 1500 IU/mL.
3. Diagnostic sensitivity: 98 %.
4. Diagnostic specificity: 97 %.
INTERFERENCES
Bilirubin (20 mg/dL), hemoglobin (10 g/L), lipids (10 g/L), rheumatoid
factors (300 IU/mL) do not interfere. Other substances may interfere7.
LIMITATIONS OF THE PROCEDURE
- False positive results may be obtained in conditions such as,
reumatoide arthritis, scarlet fever, tonsilitis, several streptococcal
infections and healthy carriers.
- Early infections and children from 6 months to 5 years may cause
false negative results.
- A single ASO determination does not produce much information
about the actual state of the disease. Titrations at biweekly intervals
during 4 or 6 weeks are advisable to follow the disease evolution.
- Clinical diagnosis should not be made on findings of a single test
result, but should integrate both clinical and laboratory data.
