Alere TestPack+Plus Strep A - Page 6

4
EN
If the test is invalid, retest with a new specimen and a new reaction disc,
ensuring sufcient specimen addition and read for presence of the above
controls. If the problem persists, call your local distributor.
EXTERNAL QUALITY CONTROL
Good laboratory practice recommends the use of control materials to ensure
proper kit performance. Each laboratory should refer to guidelines established
internally and by local, national or other accrediting organisations.
Alternatively, use a sterile swab to obtain a conrmed Group A Streptococcal
colony from a culture plate and subject this to the complete extraction and
test procedure. A fresh sterile swab can be used as a negative control. If the
external controls do not produce the expected result, the test is invalid and
the patient test result should not be reported. Repeat testing of Positive/
Negative Controls and patient specimens with new reaction discs. If the
problem persists, call your local distributor.
LIMITATIONS OF THE TEST
1. The use of swab types other than Polyester (Dacron) tipped swabs,
swabs taken from sites other than the back of the throat or the use of other
specimens such as saliva, sputum, or urine has not been established.
Negative Result
A negative result is indicated by a horizontal line (Minus Sign
“-“) in the Result Window. A negative result means that no
Group A Strep antigen was detected, or that the levels of
antigen in the specimen were below the detection limit of the assay.
2. This test does not differentiate between carrier and infected individuals.
Pharyngitis may be caused by organisms other than Group A
Streptococcus. Performance characteristics in populations other than those
studied during the clinical investigation have not been determined.
3. A negative result may be obtained if the amount of extracted antigen is
below the sensitivity of the test.
4. False negative results may occur from incorrectly taken/extracted
specimens.
5. Additional follow-up testing using the culture method is required if the result
is negative and clinical symptoms persist.
EXPECTED VALUES
It is believed that approximately 19% of all upper respiratory tract infections
are caused by Group A Streptococcus
7
. Group A Strep associated pharyngitis
displays a seasonal variation and is most prevalent during the winter and
early spring. Certain populations are at higher risk of infection for example in
schools, nursing homes and hospitals, and clustering of cases does occur
8,9
.
CALIBRATION
Alere
TM
TestPack Strep A is calibrated using in-house standards produced
from dilutions of a Group A Streptococcal antigen.
PERFORMANCE CHARACTERISTICS
Clinical performance of Alere
TM
TestPack Strep A compared with
standard sheep blood agar culture
In a multi-centre eld evaluation, throat swabs were collected from 369
children and adults presenting with symptoms of pharyngitis. All swabs were
tested on the day of collection and were used to inoculate a sheep blood agar
(SBA) plate, prior to being tested using Alere
TM
TestPack Strep A. Plates
were incubated for 24-48 hours at 35°C with 5-10% CO
2
. Presumptive group
A Streptococcus colonies on SBA culture plates were conrmed using a
commercially available Streptococcal latex grouping test.
SBA +
122
3
125
TestPack Strep A +
TestPack Strep A -
Total
SBA -
4
240
244
Total
126
243
369
The results are summarised below:
Individual test results compared to standard SBA culture:
Sensitivity: 122/125 = 97.6% (95% condence interval [CI]: 93.1-99.5%)
Specicity: 240/244 = 98.4% (95% condence interval [CI]: 95.9-99.6%).
Individual test results compared to SBA culture density:
For visually positive SBA plates, clinicians recorded the density and growth of
presumptive group A Streptococcus colonies. The results from SBA culture
and the corresponding Alere
TM
TestPack Strep A rapid results are compared
below:
Culture Density
1+
2+
3+
4+
TestPack Strep A +
82% (9/11)
96% (23/24)
100% (39/39)
100% (51/51)
Positive Result
A positive result consists of one vertical line (Patient Bar)
and one horizontal line (Minus Sign “-“) in the Result Window
forming a Plus Sign “+”. Pink/red colour (darker than the
background) on the Patient Bar is interpreted as a positive
result even if it has less colour than the Minus Sign. Randomly occurring red
dots should not be evaluated in the interpretation of results.
TP Strep A ROW 240599R4_5.indd 4 2011/08/12 12:00:23