Dengue is
caused by any of the four closely related dengue viruses (DEN-V1, DEN-V2,
DEN-V3, and DEN-V4). THE VIRUSES ARE TRANSMITTED TO HUMAN BY THE DAY BITING
MOSQUITO Aedes aegypti and Aedes albopictus. Dengue hemorrhagic fever (DHF) is
a more severe form of dengue infection and it can be fatal if undetected and
not treated in a timely manner.
Non
Structural Protein (NS1) is highly-conserved glycoprotein that is present at
high concentration in the sera of dengue infected patients during the early
clinical phase of the disease. NS1 antigen is found from the first day and last
up to 9 days after onset of fever is some of primary or secondary dengue
infected patients. NS1 antigen appears in serum / plasma before the onset of
IgM & IgG antibodies and its detection in suspected dengue patient can be
used as an early marker for the disease.
Dengue NS-1
test perform for qualitative detection of NS 1 Ag in human serum / plasma as an
aid for the early diagnosis of Dengue.
Test
principle:
This test
device contains a strip composed of a sample pad, conjugated pad,
nitrocellulose membrane (NCM) and absorbent pad. The conjugate pad contains
dried colloidal gold conjugated with anti-dengue NS 1. The NCM is immobilized
with anti-dengue NS1 Ag at the test line region “T” and another protein as
visual control at control line region “C”. Test line and the control line in
result window are not visible before applying any sample.
When a serum
/ plasma sample containing Dengue NS 1 Ag is applied in sample well of test
device, it solubilizes the gold conjugate dried on conjugate pad and makes an
immune complex. This complex moves chromatographically and is captured by the
test line protein resulting in appearance of pink / purple line at “T” region.
The appearance of pink / purple line at “C” region validates the test and is
used as procedural control and should always appear if used as procedural
control and should always appear if the test procedure is performed correctly.
If no pink / purple line appears at “T” region then the sample has no Dengue NS
1 Ag. Pink / purple line at “T” & “C” indicates positive reaction and the
specimen has NS 1 Ag.
Precautions:
1.
Test is only for in-vitro diagnosis.
2.
Disposable card for single use only.
3.
Serum or plasma is preferred choice as specimen.
4.
Do not use it beyond the expiration date.
5.
Don’t run the test under or in front of high
flow of air.
6.
Use separate disposable dropper or pipette tips
for each sample in order to avoid cross-contamination of either sample which
could cause erroneous results.
7.
Don’t eat or smoke while handling specimens.
8.
Wear protective gloves while handling specimens.
Wash hands thoroughly afterwards.
9.
Avoid splashing or aerosol formation. Clean up
spills thoroughly using an appropriate disinfectant.
10.
Decontaminate and dispose of all specimens,
reaction kits and potentially contaminated materials, as if they were
infectious waste, in a bio-hazard container.
11.
Do not use the test kit if the pouch is damaged
or the seal is broken.
Specimen
collection and storage:
Collect the
whole blood into the collection tube (with or without anticoagulants) by
venipuncture. Allow to clot or wait for RBC to settle down. Centrifuge the tube
and separate serum / plasma. Optimal results were obtained when patient samples
were tested immediately after collection. If plasma or serum specimens are not
tested immediately, they should be refrigerated at 2-80C. For
storage period longer than 2 weeks, freezing is recommended. They should be
brought to room temperature prior to use. Plasma or serum specimens containing
a precipitate may yield inconsistent test results. Such specimens must be
clarified prior to assaying.
Test
procedure:
1.
Allow the serum / plasma and test cards to come
at room temperature if stored in refrigerator.
2.
Take out the test cards from the pouch by
tearing from notch provided and place on flat surface.
3.
Using dropper, provided with the kit add 2-3
drops (about 50-75 UL) of serum / plasma into the sample well (S).
image
4.
Wait for appearance of pink / purple line in the
result window and interpret result within 5-20 minutes.
Positive:
the appearance of two pink / purple lines (one at “T” region and other at “C”
region) within the result window, no
matter which line appears first, indicates a positive result and sample has
dengue NS ! Ag.
Negative:
The appearance of one pink / purple line (at “C” region) within the result
window indicates a negative result and sample does not have dengue NS 1 Ag.
Invalid: If
the pink / purple line is not visible within the result window after performing
the test. The result is considered invalid. The directions may not have been
followed correctly or the test may have deteriorated. It is recommended that
the specimen be re-tested with a new card.
Expected
value
The NS 1is
expected to be detected 1st day after the onset of fever and persist
up to 9th days in both primary and secondary dengue infection. But
if anti-NS 1 antibody are produced, the detection of NS 1 is inhibited.
Primary
dengue is characterized by the presence of detectable IgM 3-5 days after the
onset of infection. Secondary dengue is characterized by the elevation of
specific IgG 1-2 days after the onset of infection and in the majority of cases
this is generally accompanied by an elevation of IgM.
Performance
characteristics
1.
Sensitivity and Specificity: In-house panel of
confirmed NS 1 positive and negative samples tested and found the approx.
sensitivity of 92% and specificity 98%.
2.
To evaluate the interference of dengue NS 1 Ag
rapid kit with known relevant interfering specimens, the hemolytic samples,
rheumatoid factors-contained samples and lipaemic, icteric samples were
investigated, in these studies; specimens did not interfere with this test kit.
3.
Analytical sensitivity: the limit of detection,
the smallest amount of the target marker that can be precisely detected; have
been equal or superior to a leading commercial dengue NS 1Ag detection rapid
tests.
Limitation
of the test
1.
A negative result can occur if the quantity of
dengue virus NS 1 Ag present in specimen is below the detection limits of the
assay, or the antigens that are detected are not present during the stage of
diseases in which a sample is collected.
2.
A negative test result cannot exclude a recent
infection.
3.
The presence of detectable dengue virus NS 1 Ag
may mean positive for early dengue infection. As with all diagnostic tests, all
results must be considered with other clinical information available to the
physician.
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