RAPID STREP TESTING

Effective Date: 
Thu, 03/01/2007
Reviewed: 
Tue, 01/10/2017
Policy: 

CLIA: Waived
 

Principle: The Consult Diagnostics Strep A Dipstick is a qualitative, lateral flow immunoassay for the detection of Strep A carbohydrate antigen in a throat swab. In this test, antibody specific to Strep A carbohydrate antigen is coated on the test line region of the dipstick. During testing, the extracted throat swab specimen reacts with an antibody to Strep A that is coated onto particles. The mixture migrates up the membrane to react with the antibody to Strep A on the membrane and generate a red line in the test region. The presence of the red line in the test region indicates a positive result, while its absence indicates a negative result. To serve as a procedural control, a red line will always appear in the control region if the test has been performed properly. If a red line does not appear, the test result is not valid.

Materials:

  1. Test dipsticks
  2. Disposable extraction test tubes.
  3. Extraction Reagent A: 2M Sodium Nitrate (10 ml): CAUTION: May be slightly caustic, avoid contact with eyes or mucous membranes. In case of contact, wash thoroughly with water.
  4. Extraction reagent B: 0.2M Acetic Acid (10 ml): CAUTION: May be slightly caustic; avoid contact with eyes or mucous membranes. In case of contact, wash thoroughly with water.
  5. Positive (non-viable Group A Streptococcus) and negative (non-viable Group C Streptococcus) controls. CAUTION: Contain sodium azide which may react with lead or copper plumbing to form potentially explosive metal azides. When disposing of these solutions, always flush with copious amounts of water to prevent azide build-up.
  6. Sterile throat swabs
  7. Timer

Precautions:

  • Do not use after expiration
  • Do not interchange components from different kit lots
  • Wear PPE such as lab coats and gloves.
  • Humidity and temperature can adversely affect results

Specimen:

Use sterile polyester swabs (Fisherbrand). Avoid touching the tongue, cheeks and teeth with the swab.

Swabs may be stored for 8 hours at room temperature or 72 hours at 2-8 C

 

Procedure: 

 

 

  1. Place the extraction tube in the workstation tray. Add four drops of Extraction Reagent A and four drops of Extraction Reagent B to the tube. Tap the tube to mix.
  2. Place the throat swab specimen in the extraction tube. Rotate the swab 10 times in the tube. Leave swab in tube 1 minute.
  3. Squeeze the swab firmly against the tube to expel as much liquid as possible from the swab. Discard the swab.
  4. Remove the test strip from the canister and use as soon as possible. Immerse the test strip into the extraction tube with the arrows pointing toward the bottom of the tube. Liquid level should be at or just below the MAX line on the strip.
  5. Read results in 5 minutes. Positive results may be visible in one minute. To confirm a negative result, the complete reaction time of 5 minutes is required. DO NOT READ RESULTS AFTER TEN MINUTES.

Interpretation of Results:
POSITIVE: Two red colored lines appear, one in the test (T) region and one in the control (C) region. The color intensities of the lines may vary. Any shade of red should be considered positive. A positive result indicates that the specimen contains Strep A antigen.

NEGATIVE: Only one red colored line appears in the control (C) region. No apparent red colored line is visible in the test (T) region. A negative result indicates there is no Strep A antigen in the swab sample or that the Strep A antigen concentration is below the detection level.

INVALID: No red colored line appears in the control (C) region. An absence of the control line is an indication of procedural error or possible reagent deterioration. A new test should be performed. If the problem persists, call Applied Biotech, Inc. at (888) 578-7956 for technical assistance.

Quality Control: A positive and negative external control must be tested once per box. A procedural control is included in the test. A colored line appearing on the control (C) Region is considered an internal positive procedural control indicating proper performance. A clear background in the result area is considered an internal negative procedural control. If the reagents are working properly and the test has been performed correctly, the background will clear to give a discernible result.

Limitations:

  • The test will indicate the presence of Strep A antigen in the specimen from viable and nonviable Group A Strep.
  • A negative result obtained from this kit should be confirmed by culture.
  • Excess blood or mucus on the swab specimen may interfere with test performance and may yield false positive results.

 

 

Performance Characterisitics:
Sensitivity: 97%
Specificity: 95%
Overall Accuracy: 95%

Expected Results: The incidence of Group A beta-hemolytic Streptococcus in school aged children and adults is about 40%. Most cases occur in winter and early spring and affect males and females equally.

References:

Product insert Consult Diagnostics Strep A Dipstick China 3/14