CLIA: Moderate
Principle: The QuickVue+ Strep A Test is a lateral flow immunoassay, containing a highly specific and sensitive antibody to Group A Strep antigen.
To perform the test, a Swab specimen from a throat or a beta-hemolytic colony is collected. Antigen is extracted from the Swab specimen with Reagents A and B. The extracted sample is added to the Test Cassette.
If the sample contains Strep A antigen, a pink vertical line (|) forms in the Read Result Window. The pink vertical line, together with the pre-printed blue horizontal line (-), forms a plus sign (+) to indicate a positive result. If Strep A is not present in the sample, the Read Result Window shows on the pre-printed blue horizontal line, forming a minus sign (-) to indicate a negative result.
As the sample continues to moves through the test, the control Window containing Strep A antigen becomes pink. Pink color in the Control Window indicates that the detection antibody is functionally active and is also evidence that the detection part of the test is functioning properly.
The appearance of blue color in the Test Complete Window indicates the completion of the test. This occcurs approximately 5 minutes after the addition of the extracted sample to the Test Cassette.
Reagents and Materials Supplied
Warnings and Precautions
Kit Storage and Stability:
Store kit at room temperature, 59 deg F to 86 deg F (15 deg C to 30 deg C). Kit contents are stable until the expiration date printed on the outer box. Do not freeze.
Specimen Collection and Storage:
Collect throat swab specimens by standard clinical methods. When swabbing the throat, be careful not to touch the tongue, sides or top of the mouth with the swab. Rub the Swab on the back of the throat on the tonsils and in any other area where there is redness, inflammation or pus. Bloody specimens can create an interfering background and can cause an invalid result.
Use rayon-tip or dacron-tip swabs with plastic shafts; individually packaged sterile rayon-tipped Swabs are provided in the kit. Do not use calcium alginate, cotton-tip or wodden shafted swabs. Swab specimens should be processed as soon as possible after collection.
If culture resuls are also desired, and two swabs are not submitted, lightly streat the Swab on a 5% sheep blood agar plate before using the QuickVue+ Strep A Test. The culture plate must be streaked priorn to running the QuickVue+ test, as the reagents will kill the bacteria on the Swab.
Culture Confirmation
The QuickVue+ Strep A Test can be used to confirm the indentification of Group A Streptococcus on beta-hemolytic colonies on SAB Plates. Lightly touch a colony using a sterile swab. Follow the instructions in the TEST PROCEDURE section to test the sample.
Important: Gloves should be worn when handling human samples.
Before Testing:
Note: when adding drops, hol bottle vertically so that a complete drop forms.
Perform Test
Interpretation of Results:
POSITIVE: The sample contains Group A Streptococcus antigen when you see:
AND
Note: The combination of any shade of a pink vertical line in the Read Result window and any blue shade in the Complete Result window should be interprete as a positive result.
NEGATIVE: The sample does not contain Group A Streptococcus when you see the following, 10 mnutes after adding the sample:
AND
Note: A negative QuickVue+ result indicates a presumptive negative test result for the presence of Group A Streptococcal anitigen.
INVALID RESULT:
A result is invalid it:
OR
OR
Note: In the case of an invalid result, a new patient sample should be tested using a new QuickVue+ Strep A Test, or contact Quidel Technical Support.
QC Testing Produre:
Quality Control
Built-in Control Features
The QuickVue+ Strep A Test provides three levels of internal procedure controls with each test run. For Daily quality control, document, using a drop down in the LIS, that these internal controls were checked daily with the control run.
Built in Extraction Reagent Control: The color of the Extraction Reagent changes from clear to green as the reagents are ixedtogether. The color change is an internal extraction reagent control and is an indicaton that the reagents were mixed and functioning properly.
Built-in Positive Antigen Control:Pink color in the control window werves as a built-in positive antigen control. The appearance of this control indicates that the detection antibody is functionally active and is also evidence that the detection part of the test is functioning properly.
Built-in Negative Background Control: The background area in the Read Result window should be white to light pink within 10 minutes and not interfere with the reading of the result. A lack of interfering background serves as a built-in negative background control, indicating that there are no immunological interfering substances in the sample.
External Quality control Testing
External controls are provided and may also be ued to ensure that the reagents are performing properly and that you are able to correctly perform the teset procedure. You may slo use controls derived form ATCC strain 19615.
Because this test format is considered to be Moderate Complexity, we will run 2 levels of external controls each day to satisfy CLIA standards.
Limitations:
Expected Values
Group A Streptococci cause about 19% of all upper respiratory tract infections. Streptococcal pharyngitis is seasonal in nature with the highest prevalence found during the winter and early spring The highest incidence of this disease is found in crowded populations and in school-aged children, and is evenly distributed between males and females.
Performance Characterisitics:
Sensitivity: 95%
Specificity: 98%
Overall Accuracy: 98%
In addition, the QuickVue+ Strep A Test was used to confirm the indentification of Group A Streptococcus on SBA culture plates. As a culture confiramtion, the QuickVue+Test was 100% sensitive and 100% specific.
References:
Product insert Quidel QuickVue+ Strep A Test (10/19)