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RAPID STREP TESTING **

Effective Date: 
Thu, 03/01/2007
Reviewed: 
Tue, 02/04/2020
Policy: 

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

  1. Individually Packaged Test Cassettes (25):  Rabbit anti-Strep A antibody and heat-inactivated Strep A antigen
  2. Extraction Reagent A (1):  4M Sodium Nitrite
  3. Extraction Reagent B (1):  0.2 M Acetic Acid
  4. Sterile Throat Swabs (25)
  5. Tubes and Tips (25)
  6. Positive Control (1):  Heat-inactivated Group A Streptococcus, 0.02% sodium azide.
  7. Negative Control (1):  Heat-inativated Group C Streptococcus, 0.02% sodium azide.
  8. Package Insert (1)
  9. Procedure Card (1)

Warnings and Precautions

  • For in vitro diagnostic use
  • Do not use kit contents aafter the expiraton date printed on the ourtside of the kit.
  • Use appropriate precautions in the collection, storage, handling, and disposal of patient samples and used kit contents
  • Use of Nitrile gloves is recommended when handling patient samples.
  • DO NOT interchange caps among reagents.
  • The Test Cassette must remain sealed in the foil pouch until just proior to use.
  • Reagent A contains 27.6% sodium nitrite and may be harmful if ingested or absobed.
  • Reagent B contains an acidiic solution.  If the solution contacts the skin or eye, flush with large volumes of water.
  • Do not use Reagent B is solution is green prior to mixing with Reagent A in the Tube.  If this occurs, contact Quidel Technical Support.
  • To obtain accurate results, you must follow the Package Insert instructions.
  • Testing should be performed in an area with adequate ventilation.
  • Dispose of containers and unused contents in accordance with Federal, State, and Local regulatory requirements.
  • Wear suitiaable protective clothing gloves and eye/face protection when handling the contents of the kit.
  • Wash hands thoroughly after handling.
  • Fpor additional information on hazard smbols, saftely, handling and disposal of the components within this kit, please refer to the Safetu Data Sheet (SDS) located in the Lab SDS binder.

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.

 

Procedure: 

Important:  Gloves should be worn when handling human samples.

Before Testing:

  • Remove Test Cassette from the foil pouch and placae it on a level surface.
  • Put a clean Tube in the Tube Well of the Test Cassette.  Squeeze 4 DROPS of Reagent A and 4 DROPS of Reagent B into the Tube.  The solution should turn green once Reagent B is added.

      Note:  when adding drops, hol bottle vertically so that a complete drop forms.

  • Immediately place the Throat Swab into the Tube.  Mix solution thoroughly by swirling the swab for 5 times (or vortex briefly).
  • Wait 1 minute
  • Remove the Tube from the Tube Well.  Express all liquid from the Swab head by rolling the Swaab against the inside of the Tube and squeezing firmly as it is withdrawn from the Tube.  Discard the Swab.
  • Put a clean Tip on the Tube.

Perform Test

  • Add 2 DROPS from the Tube to the round Sample Well in the test Cassette.
  • For a valid result the test must be read in 10 minutes or less after adding the sample and there must be ANY shade of blue in the Test Complete Window.
  • If there is no shade of blue in theTest complete Window at 10 mnutes, the result is invalid.

Interpretation of Results:
POSITIVE: The sample contains Group A Streptococcus antigen when you see:

  • A pink and blue plus sign (+) in the large square Read Result window along with a pink color in the small square control Window

                      AND

  • Any shade of blue color in the Test Complete Window

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:

  • A blue minus sign (-) in the large square Read Result window along with a pink color in the small square control Window

                     AND

  • Any shade of blue color in the Test Complete Window

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:

  • At 10 minutes, no shade of blue appears in the Test Complete Window.

                    OR

  • No pink color appears in the control window by 10 minutes

                    OR

  • Background color in the Read Result Window interferes with test interpretation at 10 minutes

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:

  • Follow the instructions in the TEST PROCEDURE to dispense the Extraction Reagents in to tube.
  • Vigorously mix the Control Bottles.  Add 1 drop of the Negative or Positive control into the tube.
  • Place a clean Swab into the Tube and follow the instructionsfor testin the patient Swab.

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:

  • The contents of this kit are for use in the qualitative detection of Group A Streptococcal antigen form throat swabs and culture colonies only.
  • Respiratory infections, including pharyngitis, can be aused ty Streptococcus from serogroups other than Group A as well as other pathogens.  The QuickVue+ test will not differentiate asymptomatic carries of Grop A Streptococcus from those exhibitiing Group A Streptococcal infection.
  • In rare cases, test specimens heavily colonized with Staphylococcus aureus can yeild false positive results.
  • Test results must always be evaluated with other data available to the provider.  A negative test result might occur if the level of extracted antigen in a sample is below the detection level of the test.  Additional follow-up teting using the culture method is recommended in the QuickVue+ test result is negative.

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)