Dengue Fever: When And How To Get Tested?
Dengue fever is a viral infection transmitted to humans by mosquitoes that live in tropical and subtropical climates and carry the virus. Blood testing detects the dengue virus or antibodies produced in response to dengue infection.
Dengue is a mosquito-borne viral infection which can cause a severe flu-like illness. The infection spreads through the bite of infected Aedes mosquitoes (Ae. aegypti or Ae. albopictus). There are 4 Dengue virus strains (DEN 1, DEN2, DEN3, and DEN4) commonly associated with dengue infection. Among these, DEN 2 is more commonly associated with outbreaks.
As there has been a sudden rise in the cases of Dengue infection these days, here is a quick guide to know the symptoms and to prevent transmission of the virus. This guide will also help to identify what and when to get tested if you suspect dengue-like symptoms.
What causes dengue fever?
Dengue fever is caused by one of four dengue viruses. When a mosquito infected with the dengue virus bites you, the virus can enter your blood and make copies of itself. The virus itself and your immune system’s response can make you feel sick.
The virus can destroy parts of your blood that form clots and give structure to your blood vessels. This, along with certain chemicals that your immune system creates, can make your blood leak out of your vessels and cause internal bleeding. This leads to the life-threatening symptoms of severe dengue.
Signs & Symptoms Of Dengue
The symptoms of dengue usually appear 4-10 days after being bitten by an infected mosquito. The most common symptoms associated with dengue fever may include:
– Fever as high as 104℉ or 40℃
– Severe headache
– Eye pain, typically behind the eyes (Retro-orbital pain)
– Muscle, bone, or joint pain
– Rash
– Nausea and vomiting
– Loose motions
– Decreased appetite
– Weakness
– Swollen glands
When is it ordered?
Testing may be ordered when individuals have signs and symptoms associated with dengue following travel to tropical locations where the dengue virus is present. Some of the main signs and symptoms include:
- Sudden high fever (104°F or 40°C)
- Severe headache or pain behind the eyes
- Joint, muscle and/or bone pain
- Gum and nose bleeds
- Easy bruising
- Low white blood cell count
Molecular testing is ordered within one week of the onset of symptoms to detect an acute infection, while antibody testing may be ordered more than 4 days after symptoms appear. If antibody testing is performed, an additional blood sample may be collected after two weeks of symptoms to determine if the antibody level is rising.
How To Diagnose Dengue?
A blood test is generally advised if a person is down with fever, muscle pain, and weakness or has any other symptoms of dengue. A lab test is the only way to confirm dengue infection. However, the type of Dengue test may depend on the time of infection and the appearance of the symptoms of dengue fever. Therefore, before you consider a blood test for dengue, you must know about the different types of blood tests available.
Dengue testing is divided into 2 categories:
- A) Direct Tests: Tests identifying the virus by antigen / genetic signature. These include a nonstructural protein 1 (NS1) antigen test done through ELISA, and a dengue PCR test done using RT-PCR technique. These tests are 99-100% specific with the latter having higher sensitivity.
- B) Indirect Tests:Tests related to the body’s response against the virus. These include IgM and IgG antibodies against Dengue virus measured by ELISA technique.
Here is a quick read which can guide you about the different tests suggested to identify dengue infection.
- A) Direct Tests
- Dengue NS1 Antigen
This test is performed early in the course of infection, usually within the first 5 days of the onset of symptoms. This is because NS 1 antigen starts to appear from the very first day of dengue infection and may be present for up to 5-7 days. Thereafter, it starts disappearing from the body and may therefore indicate false-negative results.
- B) Indirect Tests
- Immunoglobulin M (IgM) test for Dengue
This test detects IgM (antibodies) in the blood, which appear in the initial phase of the disease, and signifies acute infection or recent infection. It is advised to undergo a dengue antibody IgM test if you experience the symptoms of dengue continue for more than 5 days. It is usually done after the 4th day of the occurrence of the symptoms as the antibodies start developing after 4-5 days of infection.
- Immunoglobulin G (IgG) test for Dengue
The test is used to detect infection in the later course of the disease because the level of IgG which is to be monitored in the test tends to increase slowly. Usually, IgG antibodies are detectable in low quantities starting around 14-21 days of the infection, after which they slowly increase. These antibodies can remain in the blood for around 90 days and in some cases may remain for the rest of your life.
You can get an IgG antibody test for dengue after 14-21 days of infection or even later as these antibodies remain in the blood several months post infection. The presence of IgG antibodies signifies previous infection, recovery after dengue or post vaccination against dengue.
- Complete Blood Count
Dengue is frequently associated with decreased platelet count (normal platelet count lies in the range of 1.5 to 4 lacs). Therefore, platelet count should be monitored carefully and regularly, especially when the fever comes down.
If a patient is positive for dengue-specific antigen, a decrease in platelet count and a decrease in total white blood cells (WBC) count may be seen. But, it is important to know that diagnosis of dengue does not depend solely on platelet counts.
What are the Preparations Required For Dengue NS1 Antigen Test?
Dengue NS1 Antigen Blood Test is a simple test that requires no special practices. However, you may be advised to follow the general guidelines provided by your healthcare professional to avoid discrepancies in the test results. Such guidelines are:
- If you are on some medications, you may be advised to stop for the time being the sample is collected. However, you should not take or stop any medicine without their confirmation.
- In addition, you should sleep well and stay calm during the examination to ensure that all your hormones are balancedand reports are accurate.
- The test requires no fasting. However, if you are on a special diet, you may be asked to eat normally yet light to ensure your test results are not interrupted. Do not change your diet or routine without consulting your health practitioner.
- Keep your anxiety or stress away while getting tested, and if you have any doubts, feel free to discuss them with your doctors or phlebotomists.
