Dengue NS1 test

What is dengue?

The dengue virus is a very common cause of illness in tropical and sub-tropical countries all over the world. Statistics indicate that almost 390 million people are infected annually by dengue. The mosquito-borne virus can cause the onset of dengue fever in an individual which can develop into the more severe form of dengue hemorrhagic fever that causes plasma leakage.

This fever can lead to a shock syndrome which can cause death in children and aged patients. The infection can be caused by anyone of the serotypes of dengue viruses (DENV 1 to 4) which are generally carried by the female mosquito species Aedesaegypti.

What is the dengue NS1 test?

NS1 is a conserved glycoprotein that is secreted by the dengue virus and it is transferred into the blood of the infected. During the early clinical phase of the disease, a high quantity of this protein is found in the blood serum components of the patient. The link between the NS1 protein and the dengue virus has resulted in the formation of a new diagnostic tool for prompt and early detection of dengue.

The test can be done within 24 hours and up to 7 days from the onset of the infection. In many cases, antibody tests like IgM- and IgG-class antibodies are also conducted to obtain conclusive evidence for dengue infection. But NS1 can be detected even before IgM antibodies appear in the blood.

The NS1 test is widely available and can be done with the least amount of expense, making it a popular choice for doctors. In some cases, other flaviviruses like Zika, yellow fever, Japanese encephalitis, etc. can coexist with the dengue virus.

For such scenarios, the IgM-positive specimens can be tested for specific neutralizing antibodies by a plaque reduction neutralization test (PRNT) to identify the exact cause of the illness.

Why do I need to undergo a dengue NS1 test?

The test needs to be done if dengue infection is prevalent in your area and the doctor finds the initial symptoms matching with that of typical dengue fever. The incubation period of the virus varies from 3 to 7 days and then the typical symptoms of dengue fever appear. The symptoms may include the following.

– Sudden high fever rising up to 104°F which may be accompanied by nausea or vomiting.
– Severe headache or pain behind the eyes.
– Joint, muscle and bone pain.
– Skin rash development.
– Bleeding from gums and nose.
– Low white blood cell count.
– Easy bruising in the body.
– A feeling of tiredness or restlessness.

Sometimes the symptoms are mild and can be mistaken for a normal fever or infection. This can even lead to damage to lymph and blood vessels, liver enlargement and ultimately, the failure of the circulatory system.

Since the signs of the infection are non-specific, an early laboratory test for detecting the virus is very important for treatment. Those with a weak immune system or facing a second infection, are at greater risk of the disease.
 

How is a dengue NS1 test performed?

– The process of testing is simple and a blood sample usually collected from a vein in the elbow region is sent to the laboratory for testing.

– An area of the skin will be sterilized and a needle will be inserted into a vein through which blood is drawn into a syringe.

– The needle is then withdrawn and the site is covered by a bandage. In case an additional infection related to meningitis or encephalitis is suspected, then the testing of the cerebrospinal fluid is recommended.

– The initial 1 to 7 days after the symptoms show up are the acute phase of dengue. The next stage after 7 days is termed as the convalescent phase of dengue. The sample for the NS1 test needs to be collected during the acute phase.

– The test method is termed as enzyme-linked immunosorbent assay (ELISA) which provides the results within a short period of time.

In some cases, the NS1 rapid antigen detection test is done which can be performed with whole blood at the bedside of the patient, without the need for any laboratory. This test can be done within an hour and generally, a dengue NS1 Ag strip is used to detect the NS1 antigen.

What is the price for a dengue NS1 test in India? 

The price of an NS1 test in India can range from Rs 450 to Rs 1000 depending on the location and facility.

How many cases of dengue are reported each year in India?

Dengue fever is a widespread infection in India owing to the tropical climate and high population density. It has been estimated that more than 50% of the world’s population lives under a high risk of dengue. More than 10,000 deaths are reported every year because of dengue. As per WHO, 70% of these cases originate from India and Brazil.

When will I get the test results?

The results of an NS1 test are generally available within a day.

What is the normal range for a dengue NS1 test?

The NS1 antigen can usually be detected in blood within 1-2 days after the symptoms and up to a period of 7 days. The negative test results indicate that the antigen has not been detected whereas a positive result indicates the presence of dengue. Results can come negative if the specimen was collected after 7 days following the symptom onset.

What do the results mean?

The results of the test can be interpreted in the following ways.

– A positive result confirms a dengue diagnosis if it is prevalent in the area.

– A negative result from a patient is inconclusive and an IgM antibody test needs to be conducted. A negative test from all ends may mean that the symptoms are from some other infection. The person may still have a dengue infection but the detectable level of antibody in the body may be negligible from the initial exposure to the virus.

– Patients with a negative report of the NS1 tests and the IgM antibody tests should be tested again for the IgM antibody during the convalescent phase.

– In case an NS1 test is negative but the IgM antibody test comes positive, the doctor can order a PRNT test to identify the exact cause of the disease.

– The doctor will interpret the results with reference to the patient’s medical history and recent travel history to make a final diagnosis.

Do I need to fast for the dengue NS1 test?

Fasting is not necessary for the test.

What else do I need to know before I appear for a dengue NS1 test?

The following points can be kept in mind before appearing for the test.

– The test is safe and non-intrusive. You might feel slight discomfort from the insertion of the needle in the vein. The test does not have any side effects and any pain or discomfort at the collection site is cured within a few days. In rare cases, some infections might develop in the collection site which needs treatment.

– The physical symptoms like rashes or joint pain are not sufficient to detect dengue as many of them appear after the initial stage of the fever. The broad spectrum of symptoms the virus generates makes it difficult to detect without tests and can be confused with non-dengue infections, particularly in non-epidemic situations.

– Prompt diagnosis is crucial for early intervention and can be a lifesaving step in critical cases. Additional non-specific tests like the blood count are also done to check the overall condition of the patient.
There is no immunization available for dengue at this stage and protection from mosquito bites is an important step that needs to be taken to stay safe in infected zones.

– On average, 1 in 20 people affected by dengue will develop the severe form of the disease and it needs to be treated as a medical emergency.
 

Can pregnant women undergo a dengue NS1 test?

Pregnant women can undergo the test without any restrictions.

Is dengue NS1 test possible for new-born babies?

New-born babies can undergo the test as per the instructions of the doctor.