Dengue NS1 Antigen Strip

Hi Everyone! Goodness, I can't believe our SIP is ending soon. I'm already getting so used to working in a clinical lab. Heh.

Anyways, today I will be blogging about another testkit. I know I keep blogging about testkits la but at my workplace, almost everything is automated, even the pre-analytical stuff. Thus, I get very little hands-on tests to perform. Other than testkits, of course =).

Correct me if i'm wrong but I think somebody has already blogged abt the Dengue Duo Cassette which is a testkit for Dengue Serology (IgG/IgM). Soo, I will blog about the Dengue Antigen NS1. Yay.

Name of Test: Dengue Antigen Detection/ Dengue NS1 Ag Detection

Introduction:
Singapore has recently been hit with a dengue plaque with the number of cases rising steadily to about 13 000 and 19 already succumbed to this illness. Common indications include a high fever and a hematology report stating a sudden, steep drop in platelet count with or without an increased hematocrit. The patient may also have dengue antibody (IgM for first infection or Igm and IgG for secondary and subsequent infection) present in the serum. During the acute phase of dengue, when the antibody titer is too low to be detected using testkits, the NS1 antigen is used as a marker. This antigen is present from the onset of the fever and remains in the serum up to 9 days after the onset of fever.

Principle, Method and Result Interpretation:

• The method adopted in this testkit is lateral flow immunochromatography. The testkit comes with 25 test strips and a migration buffer.
• The test strip itself has membrane that was formed with a sample pad, a conjugate pad and a membrane where the result lines will be displayed.
• The sample pad is for loading the sample. The conjugate pad contains gold colloidal particles that are coated with anti-NS1 monoclonal antibodies and also gold colloidal particles coated with streptavidin.
  
• Method:
• 50 microliters of the sample and 1 drop of migration buffer is dispensed into a small glass tube.
  
• A strip is placed into the glass tube in an upright position in the correct orientation and incubated for 15 minutes.
  
• Should the Control Line not appear after 15minutes or appear faint and doubtful, re-incubate for a further 15minutes and interpret the results.
  
• If the Control line fails to appear after 30 mins of incubation in total, discard the strip and repeat the test with a new strip.
• Results:
• If present, the NS1 antigen will bind with the gold colloidal particles coated with anti-NS1 antibodies as the sample migrates up the strip (aided by the migration buffer) to the conjugate pad. As it reaches the Result membrane, a blue or purple line will appear.
• The Control line should appear as biotin from the migration buffer reacts with streptavidin to form a blue or purple line at the Result membrane.
• A positive result is indicated with 2 lines on the result membrane.
• A negative result is indicated with 1 line on the result membrane as the Control Line.
  
• This test can be used in conjuction with other laboratory data to aid in diagnosis of dengue even though it has a few limitations.
  

Clinical Significance:
In the laboratory, this test is used as a rapid test to detect the presence of NS1 antigen in serum. Previously, this was a test sent out to our referral laboratory where RT-PCR was used to determine the presence of NS1 Antigen. This test is a useful qualitative test that significantly helps in the diagnosis of dengue during this dengue plague in Singapore because it is a test that produces an accurate result quickly. This, in turn, aids in ensuring proper treatment for the patient more efficiently.

Cheers,
Sharifah
TG01