Dengue Tests Explained: When and Which Test Should You Use?

Dengue infects roughly 400 million people each year, making it the most common mosquito-borne disease. Nicknamed “breakbone fever”, symptoms may include severe joint pain, high fever, and internal bleeding. Infection can be fatal, with an estimated 10,000 deaths each year. There is no cure for dengue, but early detection and testing can save lives. If you are experiencing symptoms of dengue, it’s important to understand which tests you need and when to take them.

Dengue Symptoms

Some people experience no symptoms of dengue, or flu-like symptoms that are mistaken for other illnesses. But dengue does have a few tell-tale signs, such as high fever, severe joint pain, and pain behind the eyes. There is also a characteristic dengue rash that resembles sunburn with goosebumps. Symptoms usually appear 4-10 days after you’ve been bitten by an infected mosquito. Be on the lookout for:

• High Fever (40C)
• Muscle, bone or joint pain
• Headache
• Nausea
• Vomiting
• Pain behind the eyes
• Swollen glands
• Rash

Dengue symptoms vary, and you can be infected without experiencing the so-called classic symptoms. The majority of people recover within a week. Mild cases can be treated at home, though dengue infection always warrants a consult with a doctor to avoid severe illness.

Severe Dengue Symptoms

Approximately 1 in 20 patients develop a life-threatening condition known as dengue hemorrhagic fever or severe dengue. This happens when dengue damages your blood vessels, causing them to leak. Internal bleeding, organ failure, and death may follow.

Severe dengue is a medical emergency. The symptoms can come on suddenly, usually, a day or two after your fever resolves and your temperature is already back to normal. Many people think they are in the recovery stage of the illness when severe dengue strikes. The following symptoms should be taken seriously and require urgent medical care.

• Bleeding under the skin, unexplained bruising
• Blood in your urine, stools, or vomit
• Bleeding from the gums or nose
• Persistent vomiting
• Difficulty breathing
• Irritability and restlessness
• Severe fatigue

Types of Dengue Tests

The best way to avoid serious illness is to get tested quickly after symptoms develop. Early diagnosis and treatment of dengue reduces the mortality rate to almost zero. Tests are available for both active and previous infection with the dengue virus.

Why do you need to know if you were infected in the past? Secondary (or past) infection increases your risk for severe illness. Testing for both active and previous infection gives the full clinical picture, and yields better treatment outcomes.

Some of the primary tests used in dengue diagnosis are the NS1, IgM, IgG, and the comprehensive test, SD BIOLINE Dengue Duo.

What is the Dengue NS1 test?

The dengue NS1 test looks for viral proteins (or antigens) in the patient's blood. It is used in the first 0-7 days of symptom onset, when you are in the active stage of dengue infection. A dengue NS1 test is not considered reliable after the 7th day of symptoms.

Interpretation of results

• A positive NS1 test result means you likely have a current dengue virus infection.
• A negative NS1 test result can mean you aren’t infected, or you tested too soon or too late in your infection.

What is the IgM test?

Your immune system produces IgM antibodies in response to dengue infection. The IgM antibodies are detectable 4-5 days after symptoms begin. The IgM test will continue to detect them for 12 weeks or longer. This test can detect both active and recovered dengue patients.

Interpretation of results

• A positive IgM test means you have likely been infected with dengue recently, but does not confirm active infection.
• A negative IgM test could mean you are not infected or you tested too soon.
• IgM antibody levels also indicate whether this is a primary (first) or secondary (past) infection.  

What is the Dengue IgG test?

The Dengue IgG test is also an antibody test. IgG antibodies are generally produced within 3 weeks of exposure and are present for life. This test identifies recovered patients.

Interpretation of results

• A dengue IgG positive test detects recovered patients, not active infections.
• A negative test result means you have not been infected with dengue in your lifetime OR you were tested too soon (within the 3 week window period).
• IgG antibody levels also indicate whether this is a primary or secondary infection.

Combination Testing: What is the SD BIOLINE Dengue Duo test?

SD BIOLINE Dengue Duo test is an all-in-one test that detects both NS1 antigens and IgG/IgM antibodies. It is a commercial test that can be performed in the home or a point-of-care setting. The Dengue Duo test identifies both current and past infections in just minutes.

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Interpretation of results

Please note that the Dengue Duo test had two results windows.

NS1 Ag Results Window

• Negative result : The presence of one control line (labeled “C”) indicates that dengue antigens were not found. A negative result can mean you are not infected or that dengue antigens are below the detectable level.

• Positive result : The presence of two lines (“C” and “T”) indicate that NS1 antigens have been found. This suggests a current dengue infection.

• Invalid result : No control line (“C”) means the test is invalid and you need to retest.

IgG/IgM Results Window

• Negative result: The presence of one control line (labeled “C”) indicates that IgG and IgM antibodies were not found or are below detectable levels. If you are showing symptoms of dengue, retest in 3-5 days.

• IgM positive result: The presence of two lines (“C” and “M”) indicates that IgM antibodies have been found. This suggests a primary dengue infection.

• IgG positive result : The presence of two lines (“C” and “G”) indicates that IgG antibodies have been found. This suggests a secondary (or past) dengue infection.

• IgG and IgM positive result : The presence of three lines (“C”, “M” and “G”) in the result window indicates that both IgM and IgG antibodies are present. This suggests a late primary or secondary dengue infection.

• Invalid result : No control line (“C”) means the test is invalid and you need to retest.

Is a home dengue test kit accurate?

A home dengue test kit can be just as accurate as a laboratory test for dengue. The SD BIOLINE Dengue Duo test is an example of a highly reliable home test. With a combined sensitivity/specificity of 88.65% and 98.75%, it is comparable to a laboratory test. However, not all dengue test kits are created equal, and many dengue test kits get damaged by the Philippines’ heat. Finding a trusted supplier who can guarantee authenticity and appropriate handling is critical for the accuracy of your dengue test kit.

Benefits of a home dengue test kit

-Home tests deliver faster results: Time is critical in the treatment of dengue. Early detection and appropriate medical care decreases the mortality rate of severe infection from 20% to less than one percent. A rapid dengue test can rapidly identify the virus. In the case of the Dengue Duo test, it also alerts you if you're at a higher risk for severe disease.

-Home test kits are more affordable and convenient: Dengue symptoms can be debilitating. A rapid dengue test can be performed from the comfort of your home. They also have a lower overhead than a lab test, bringing down the dengue test price considerably.

What to do if you suspect dengue fever

Get tested. Quick diagnosis and treatment are your best defense against severe dengue. If you opt for a home test, a doctor can help you interpret the results and prescribe treatment. If your symptoms don’t match the test results, confirmatory testing is also available through a full blood draw and laboratory analysis. If you experience symptoms of severe dengue seek immediate medical intervention. Do not await test results--head to a hospital for treatment.