INTENDED USE • The QuickVue Flex Strep A Test allows for the rapid detection of group A streptococcal antigen directly from the patient throat swab specimens. The test is intended for use as an aid in the diagnosis of group A streptococcal infection.
BACKGROUND • Group A beta-hemolytic streptococci (Streptococcus pyogenes) is one of the most commonly encountered pathogens in humans.
BACKGROUND (cont.) • Group A Streptococcus inhabits the skin and upper respiratory tract of humans but is rarely considered as normal flora. It is transmitted person to person by direct contact with mucosa, secretions or by contamination droplets produced by coughs or sneezes. The presence of Group A Streptococcus is almost always considered clinically significant.
BACKGROUND (cont.) • When present, Group A Streptococcus can cause a variety of illnesses. It is the most common cause of skin infections such as impetigo and erysipelas. It can cause illness such as tonsillitis, pharyngitis, and scarlet fever which can lead to more serious complications including rheumatic fever and acute glomerulonephritis.
BACKGROUND (cont.) • Group A Streptococcus has also been called “ flesh eating bacteria” because of it’s ability to progress into deeper tissue and organs which can cause systemic and life threatening infections.
BACKGROUND (cont.) • Early diagnosis and treatment of Group A Streptococcus infections is therefore very important and helps to prevent further complications of many of the previously mentioned illnesses. The QUICKVUE FLEX Strep A Test is a rapid screening test used for the detection consumes little time when compared with the 24-48 hours waiting period of more conventional methods that require microscopic examination, culture, and isolation of the bacteria.
PRINCIPLES OF THE TEST • THE QUICKVUE FLEX Strep A Test is a lateral-flow immunoassay. The test, containing a highly specific and sensitive antibody reactive to the Strep A antigens, is specific to Group A. To perform the test, a throat swab specimen is collected. The extraction reagents are mixed in a tube, resulting in a green color change, and the swab is added in order for the antigenic component of the bacteria to be extracted.
PRINCIPLES OF THE TEST (cont.) • Extraction occurs within one minute, after which the extracted sample is added to the Sample Well of the Test Cassette. The extracted sample migrates by capillary action through a pad consisting of a pink label containing rabbit polyclonal anti-strep A antibody and a blue control label. If the extracted solution contains strep A antigen, the antigen will bind to the antibody coupled to the pink test label which, in turn, will bind a second rabbit polyclonal anti strep A antibody spotted on the membrane, resulting in the formation of a pink-to-purple Test line.
PRINCIPLES OF THE TEST (cont.) • A blue Control Line will also appear next to the letter “C” on the Test Cassette indicating that the reagents were mixed and added properly, proper volume of fluid entered the Test Cassette and capillary flow occurred. A blue Control Line should always appear in a properly functioning Test Cassette. If strep A is not present or present at very low levels, only a blue Control Line will be visible.
REAGENTS & MATERIALS • Come in individually packaged Test Cassettes • Rabbit polyclonal antibody to strep A (Test Line) and a control rabbit polyclonal antibody capable of binding the blue control label (Control Line) • EXTRACTION REAGENT A • ( 4M Sodium Nitrite) • EXTRACTION REAGENT B • (.2M Acetic Acid) • Sterile rayon-tipped swabs on solid plastic shafts • Tubes and tips • Positive Control Swabs • Negative Control Swabs • Package Insert • Procedure Card
TEST PROCEDURE • Streak a BAP prior to beginning the extraction procedure. • For each specimen and control: • Add 4 drops of Extraction Reagent A into a clean Tube • Add 4 drops of Extraction Reagent B. The solution should turn green when Extraction Reagent B is added.
PROCEDURE, cont. • Immediately add the throat swab specimen to the Tube containing the green extraction solution. • Rotate the swab three times. • Wait one minute.
PROCEDURE, cont. • Express all liquid from the swab head in the Tube by rolling the swab against the inside of the Tube and squeezing firmly as it is withdrawn. • Discard the swab.
PROCEDURE, cont. • Put a clean tip on the Tube.
PROCEDURE, cont. • Remove Test Cassette from foil pouch and place on a clean, dry surface. • Add 2 drops from the Tube to the round Sample Well on the Test Cassette.
PROCEDURE, cont. • Read results at 5 minutes. Some positive results may be seen earlier, but negative results must be held the entire 5 minutes and no longer.
INTERPRETATION OF RESULTS • Positive results: appearance of any pink to purple Test Line next to the “T” in the result window. • Positive QuickVue Flex Strep A Test result indicates that the specimen contains group A streptococcal antigen.
INTERPRETATION OF RESULTS (cont.) • Negative Result: Only the blue Control Line appears next to the letter “C” in the Result Window.
INTERPRETATION OF RESULTS (cont.) • A negative QuickVue Flex Strep A Test result indicates that the specimen is a presumptive negative for the presence of group A streptococcal antigen, pending the result of the BAP streaked prior to the beginning of the extraction procedure.
INVALID RESULT • The test result is invalid if any shade of blue Control Line next to the letter “C” is not visible at 5 minutes. If this occurs, retest using a new specimen and a new Test Cassette.
PROCEDURE LIMITATIONS • This procedure used for qualitative detection of group A streptococcal antigen from throat swab specimen only. Failure to follow the test procedure and interpretation of test results may adversely affect performance and /or produce invalid results.
PROCEDURE LIMITATIONS • QuickVue Flex Strep A Test will not differentiate asymptomatic carriers of group A Streptococcus from those exhibiting streptococcal infection. In rare cases, test specimens heavily colonized with Staphylococcusaureus can yield false positive results.
PROCEDURE LIMITATIONS • A negative test result might occur if the level of extracted antigen in a sample is below the sensitivity of the test. Additional follow-up testing using the culture method is recommended if the QuickVue test result is negative.
CONCLUSION QUICKVUE FLEX TEST: • Is a rapid, specific and sensitive test for detection of Group A Streptococcus ( Streptococcus pyogenes) antigen directly from patient throat swab specimen. • It allows the physician to do quick diagnoses based on the results. • It avoids the 24-48 hours incubation time for blood culture plate tests. • This test is much more expensive than blood agar.