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C. Difficile Quik Chek Complete
1.
Purpose
1.1
1.2
1.3
2.
Methodology/Theory
1.1.1 The Wampole C. Diff Quik Chek Complete test is a rapid membrane enzyme
immunoassay for the simultaneous detection of Clostridium difficile glutamate
dehydrogenase antigen and toxins A and B in a single reaction well. The test
detects C. difficile antigen, glutamate dehydrogenase, as a screen for the
presence of C. difficile and confirms the presence of toxigenic C. difficile by
detecting toxins A and B in fecal specimens from persons suspected of having C.
difficile disease. This test is used as an aid in the diagnosis of C. difficile disease.
As with other tests for C. difficile, results should be considered in conjunction with
the patient history.
1.1.2 The C. Diff Chek Complete test uses antibodies specific for glutamate
dehydrogenase and toxins A and B of C. difficile. The device contains a Reaction
window with three vertical lines of immobilized antibodies. The antigen test line
(“Ag”) contains antibodies against C. difficile glutamate dehydrogenase. The
control line (“C”) is a dotted line that contains anti-horseradish peroxidase (HRP)
antibodies. The toxins A and B test line (“Tox”) contains antibodies against C.
difficile toxins A and B. The conjugate consists of antibodies to glutamate
dehydrogenase and antibodies to toxins A and B that have been coupled to
horseradish peroxidase.
Clinical Implications
1.2.1 After treatment with antibiotics, many patients develop gastrointestinal problems
ranging from mild diarrhea to severe pseudomembranous colitis. Many cases of
the milder forms of gastrointestinal illness and most cases of pseudo
membranous colitis are caused by Clostridium difficile. This organism is an
opportunistic anaerobic bacterium that grows in the intestine once the normal
flora has been altered or reduced by the antibiotic. The disease results from the
toxins produced by the organism. The clinical symptoms associated with the
disease are believed to be primarily due to toxin A, which is an enterotoxin that
damages the tissue. Clostridium difficile also produces another toxin, known as
toxin B. Toxin B, has been referred to as the cytotoxin of the organism and is the
toxin detected by the tissue culture assay used by many laboratories. Most
strains either produce both toxins or no toxin, although recently toxin A
negative/toxin B positive strains have been identified. These toxins A negative/B
positive strains test positive in this assay.
Historical Background
1.3.1 Clostridium difficile strains that produce high levels of toxin A also produce high
levels of toxin B. Likewise, strains that produce low levels of toxin A produce low
levels of toxin B, indicating that the toxin production may be regulated similarly.
Tests that can detect either or both toxins are now being used as diagnostic aids.
The genes for the toxins have been cloned and sequenced; however, some
properties of the toxins are now well defined. There is some evidence suggesting
that toxins A and B act synergistically and that the initial tissue damage caused
by toxin A allows toxin B to exert its toxicity. Therefore, although toxin A is
believed to cause most of the clinical signs, toxin B may also play an important
role in the disease.
Specimen
2.1
2.2
Stool specimen.
Collection Instructions
2.2.1 Standard collection and handling procedures used in-house for stool specimens
are appropriate. Specimens collected in preservative are unacceptable for this
assay.
C. Difficile Quik Chek Complete
2.2.2
2.2.3
3.
Reagents
3.1
3.2
3.3
3.4
3.5
3.6
3.7
4.
Wampole C. Diff Quik Chek Complete kit which contains the following:
Membrane Devices-each pouch contains 1 device.
Diluent (22 mL per bottle)-Buffered protein solution with graduated dropper assembly.
Wash Buffer (12 ml per bottle)- Buffered solution with graduated dropper assembly
Substrate (3.5 mL per bottle)- Solution containing tetramethylbenzidine.
Conjugate (2.5 mL per bottle)-Mouse monoclonal antibody specific for glutamate
dehydrogenase coupled to horseradish peroxidase and goat polyclonal antibodies
specific for toxins A and B coupled to horseradish peroxidase in a buffered protein
solution.
Positive Control (2 mL)- Antigen in a buffered protein solution.
Quality
4.1
5.
Specimens should be stored between 2C and 8C. Test specimens that are less
than 24 hours old, whenever possible. (Store specimens at -20°C, or lower, if the
test cannot be performed within 72 hours of collection). Freezing and thawing of
the specimen, especially multiple times, may result in loss of activity due to
degradation of the toxins. If using frozen specimens, thaw at room temperature.
Rejection Criteria
2.2.3.1 If more than one order for C. difficile is received on a patient within 7
days, the order should be cancelled.
2.2.3.2 If patient is less than 1 year old and doesn’t have Pathologist approval.
2.2.3.3 Stool samples received in preservative.
2.2.3.4 Stool doesn’t pass the tilt test or is hard formed.
Control (Internal and External)
4.1.1 Controls: Internal
4.1.1.1 A dotted blue line must be visible in the middle of the reaction Window,
below the “C” on every Membrane Device that is tested. The
appearance of the blue control dots confirms that the sample and
reagents were added correctly, that the reagents were active at the
time of performing the assay, and that the sample migrated properly
through the Membrane Device. A clear background in the result area is
considered an internal negative control. If the test has been performed
correctly and reagents are working properly, the background will be
white to give a discernible result.
4.1.2 External Control is used to check the reactivity of the C. DIFF QUIK CHEK
Complete kit. The Positive Control is supplied with the kit (gray-capped bottle.)
The Positive Control is supplied with the kit (gray-capped bottle). The Positive
Control confirms the reactivity of the other reagents associated with the assay,
and is not intended to ensure precision at the analytical cut-off. Diluent is used
for the negative control.
4.1.3 Preparation and Storage: Kit controls and diluent are ready for use.
4.1.4 Method and Frequency: Controls should be run with each batch.
4.1.5 Acceptance Limits: A dotted blue line must be visible in the middle of the reaction
Window, below the “C” on every Membrane Device that is tested.
4.1.6 Corrective actions: Failed QC should be repeated.
4.1.7 Documentation: QC results will be documented in the LIS.
Procedure
5.1
5.2
Bring all reagents and the required number of membrane devices to room temperature
before use.
Set up and label one small test tube for each specimen, and for external controls.
C. Difficile Quik Chek Complete
5.3
5.4
5.5
5.6
5.7
5.8
5.9
5.10
5.11
5.12
6.
Using the black graduated dropper assembly, add 750 uL (2 nd graduation from the tip)
Diluent to each tube for the fecal specimens.
Add one drop of Conjugate (red capped bottle) to each tube.
Obtain one disposable plastic transfer pipette (supplied with the kit) for each sample-the
pipettes have raised graduations at 25 uL, 400 uL and 500 uL.
Mix all specimens thoroughly and pipette 25 uL of specimen with transfer pipette. Use the
same transfer pipette to mix the diluted specimen.
If adding Control-add one drop of Positive Control or 25 uL of diluent for the negative
control. Vortex the tube to ensure proper mixing of sample and conjugate.
Obtain one Membrane Device per specimen, and one device for controls as necessary.
Label or number each device to ensure patient identification throughout the process.
Using a new transfer pipette, transfer 500 uL of the diluted sample-conjugate mixture into
the Sample well (smaller hole in the top right corner of the device) of a membrane
device, making certain to expel the liquid sample into the wicking pad.
Incubate the device at room temperature for 15 minutes-the sample will wick through the
device and a wet area will spread across the Reaction window. NOTE- some samples
may fail to migrate due to clogging of the membrane. In this case, add 4 drops (100 uL)
of Diluent to the Sample well and wait an additional 5 minutes.
After the incubation, add 300 uL of Wash Buffer to the Reaction Window using the
graduated white dropper assembly. Allow the Wash Buffer to flow through the Reaction
window membrane and be absorbed completely.
Add 2 drops of Substrate (white-capped bottle) to the Reaction Window. Read and
record results visually after 10 minutes.
Results
6.1.1
6.1.2
6.1.3
6.1.4
6.1.5
6.1.6
Interpretation of the test is most reliable when the device is read immediately at
the end of the 10-minute reaction period. Read the device at a normal working
distance in a well-lit area.
Observe device for the appearance of blue dots in the middle of the Reaction
Window representing a valid internal positive control. Observe the device for the
appearance of blue lines on the “Ag” left side and “Tox” located on the right sides
of the Reaction Window representing the test lines. The result(s) lines may
appear faint to dark blue in intensity.
Positive Antigen (“Ag”) Result: A positive antigen result may be interpreted at any
time between the addition of substrate and the 10-minute read time. For a
positive antigen result, the blue “Ag” line and the dotted blue control line below
“C” are visible. A partial line is interpreted as positive. A positive result indicates
the presence of C. difficile.
Positive Antigen and Toxin result will have an additional line on the right side of
the control dots. These results will report C. diff Interpretation as C. diff positive.
A test cannot be interpreted as negative or invalid until 10 minutes following the
addition of Substrate. A single blue dotted line is visible in the middle of the
Reaction Window, below the “C” and no test lines are visible on the “Ag” side or
the “Tox side of the Reaction Window. A negative result in the antigen portion
indicates either C. difficile antigen is either absent in the specimen or is below the
detection limit of the test. A negative result in the toxin portion indicates C.
difficile toxin is either absent in the specimen or is below the detection limit of the
test. These results will report C. diff Interpretation as C. diff negative: reconsider
testing if more than 7 days since last specimen and symptoms persist.
Invalid Result: No lines are visible in the Reaction Window. The test result is
invalid if a blue dotted line is not present below the “C” at the completion of the
reaction period.
C. Difficile Quik Chek Complete
6.1.7
6.2
7.
Method Parameters
7.1
7.2
7.3
8.
Reference Range: Negative for GDH and Toxin AB
Critical Value: Positive results are considered critical and must be called and documented
as such in the laboratory report. The result will post with a “C” next to it indicating a
critical result. Document in the result comment tab that the result was called to the LCG.
Type lab crit, press F9. In the first blank type C. diff, press F3 to get to the second blank
and type the name of the person you are calling. Press F5 to time stamp the time you are
making the call in the next blank field. The last field is for your initials.
Analytical Sensitivity: The cutoff for the assay was established at concentrations of 0.63
ng/mL for toxin A, 0.16 ng/mL for toxin B, and 0.8 ng/mL for glutamate dehydrogenase.
Reporting
8.1
9.
A positive antigen test in the absence of toxin will interpret as C. diff equivocal
and awaiting confirmation by PCR. Take the sample to the sendout area to be
sent to Mayo labs.
6.1.8 A low percentage of specimens may test negative for antigen but positive for
toxin. These samples should be considered indeterminate and retested using a
fresh specimen. If sample retests antigen negative and toxin positive, report as
positive for toxin.
Expected values
6.2.1 Clostridium difficile disease is primarily a noscomial disease of elderly patients,
and the frequency of the disease is dependent on factors such as patient
population, type of institution and epidemiology. The reported incidence of C.
difficile disease in patients with antibiotic-associated diarrhea may range from 520%, and hospitals may experience lower or higher than this range. It is
important to consider any test results in conjunction with clinical symptoms
because some healthy adults and large numbers of healthy infants will be
positive for C. difficile toxin. In addition, C. difficile carriage rates of 22% to 32%
have been reported in cystic fibrosis patients.
Interpretive Data:
8.1.1 GDH and Toxin positive will interpret as C. diff Positive.
8.1.2 GDH and Toxin negative will interpret as C. diff Negative.
8.1.3 GDH positive and toxin negative will report as C. diff equivocal and awaiting
confirmation by PCR. Take sample to sendout area to be sent out to Mayo labs.
8.1.4 GDH negative and toxin positive will result as indeterminant, please submit
another specimen for retesting.
Procedure Notes
9.1
9.2
9.3
9.4
9.5
9.6
9.7
Reagents from different kits should not be mixed or interchanged. Do not use a kit past
the expiration date.
Inspect each component in the kit for any signs of leakage. Upon arrival, inspect the kit to
ensure that components are not frozen or warm to the touch due to improper shipping
conditions.
Bring all components to ROOM TEMPERATURE BEFORE USE!
Caps, tips and dropper assemblies are color-coded; do not mix or interchange.
Do not freeze the reagents. The kit should be stored between 2C and 8C.
The pouch containing the Membrane Device should be at room temperature before
opening. Keep the membrane devices dry before use.
Use fecal specimens within 72 hours of collection to obtain optimal results. Specimens
that are frozen may lose activity due to freezing and thawing. If using frozen specimens,
thaw at room temperature.
C. Difficile Quik Chek Complete
9.8
9.9
9.10
9.11
9.12
Do not use specimens that have been preserved in 10% Formalin, merthiolate formalin,
sodium acetate formalin or polyvinyl alcohol.
Specimens in transport media such as Cary Blair and C&S can be used as specified in
the specimen preparation protocol.
Hold reagent bottles vertically to dispense reagents to ensure consistent drop size and
correct volume.
Specimens and membrane devices should be handled and disposed of as potential
biohazards after use. Wear disposable gloves while performing the test.
Membrane devices cannot be reused.