PRINCIPLE OF THE METHOD
The ASO-latex is a slide agglutination test for the qualitative and semi-quantitative
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 β-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
(skin, heart, joints, etc…) and acute glomerulonephritis is a renal infection that affects
mainly to renal glommerulus.
PRECAUTIONS
Control +/-: H317: May cause an allergic skin reaction. Contain 2-Methylisothiazol-3(2H)-one (Proclin 950). Follow the precautionary advice indicated on the SDS and product label.
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 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
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 and one drop of each Positive and Negative controls into
separate circles on the slide test.
Mix the ASO-latex reagent vigorously or on a vortex mixerbefore using and add one
drop (50 µL) next to the sample 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 in 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 an ASO concentration equal or greater than 200 IU/mL.
The titer, in the semi-quantitative method, is defined as the highest dilution showing a
positive result.
CALCULATIONS
The approximate ASO concentration in the patient sample is calculated as follows:
200 x ASO Titer = IU/mL
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 150 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.
