How to Diagnose Dengue Fever With Lab Tests

Billions of people around the world are at risk for dengue fever, a flu-like illness transmitted by the bite of a mosquito. As travel to tropical and subtropical locations has become more common, cases of dengue fever can appear anywhere and might be unfamiliar to health care providers in colder climates. Many dengue infections are mild or completely asymptomatic, but full-blown dengue fever and more serious cases of dengue hemorrhagic fever can be life-threatening if not appropriately treated. With no vaccine or specific antiviral treatments available, early identification and supportive therapy are the keys to faster recovery and prevention of serious complications. Accurate diagnosis depends on recognizing who might be at risk, the signs and symptoms of dengue and appropriate use of laboratory testing.

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If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Dengue Infections

Dengue infections, including dengue fever and dengue hemorrhagic fever, develop after a person is bitten by an Aedes species of mosquito carrying one of the four strains of dengue virus. According to the World Health Organization, approximately 40 percent of the world’s population lives in regions at risk for dengue and as many as 50 million infections occur each year 1. Countries of Central and South America, the Caribbean, Africa, Southeast Asia, the Western Pacific and the Eastern Mediterranean are home to mosquitoes that harbor the dengue virus. Cases have been reported since 1980 in Hawaii, Texas and Florida. Although mosquito bites are the usual means of transmitting the dengue virus, infections can also be transmitted by contaminated blood during transfusions, organ transplants or needle stick incidents. The virus can also pass from an infected mother to her unborn baby. A person’s first infection with one of the four dengue viruses usually results in no symptoms or a mild flu-like illness. A subsequent infection with any of the other three dengue viruses is more likely to cause serious illness. Anyone developing a high fever after living or traveling in a region where dengue is common within the previous two weeks should consider dengue fever a possibility.

Symptoms and Signs

Symptoms of dengue usually appear within four to seven days after a person is bitten by an infected mosquito, but may not develop for up to two weeks in some cases. Mild forms of dengue might mimic a mild case of the flu, but classic dengue fever begins with a sudden, high fever and two or more other symptoms including severe headache, pain behind the eyes, muscle and joint aches, a patchy red rash that appears as the fever begins to drop, nausea and vomiting. The muscle and joint pains can be so intense that dengue fever is sometimes referred to by the nickname breakbone fever. More severe symptoms may appear after a few days of fever in about 1 percent of cases, signaling dengue hemorrhagic fever 2. Typical signs and symptoms of dengue hemorrhagic fever include persistent vomiting, abdominal pain, bleeding from the nose and gums, shortness of breath and fluid buildup in the chest and abdomen. Untreated dengue hemorrhagic fever can have a fatality rate of 20 percent or greater; with good supportive medical care, the death rate is less than 1 percent.

Lab Tests for Dengue

Several laboratory tests are helpful in diagnosing dengue infection, but only a few identify the virus itself. Although many infections cause an increase in the white cell blood count, people with dengue fever commonly have a low level of circulating white blood cells. The clot forming elements in the blood, the platelets, are also characteristically low. The percentage of the blood comprised of red cells, the hematocrit, is increased due to fluid leakage into the body tissues. Blood sodium levels are often lower than normal, and liver enzyme levels may be increased due to inflammation.
The most commonly performed test to confirm a diagnosis of dengue fever looks for antibodies against the dengue virus in the patient's blood. Although this test can positively identify a dengue infection, antibodies take at least five days to appear in the blood. In the United States, dengue antibody tests have historically been performed only by specialty labs, state public health departments and the Centers for Disease Control and Prevention 2. The test, however, is expected to become more widely accessible because the U.S. Food and Drug Administration approved a new, commercial form of the test in April 2011.

Additional Laboratory Tests

Dengue infections can be diagnosed using other laboratory tests specific for the virus. These tests look for fragments of dengue genetic material or proteins in the patient's blood, or grow the virus in specialized cell cultures. The results are highly accurate and specific, which is an advantage over the more common antibody tests that sometimes falsely identify other viruses such as West Nile or yellow fever as dengue. However, these tests are not used as often as dengue antibody tests because of higher costs, more complicated procedures, a longer time before results are available or a combination of these factors.

Treatment of Dengue Fever

No protective vaccine or virus-specific treatment is available for dengue infection. Once diagnosed, treatment consists primarily of bed rest, hydration, acetaminophen for fever and pain medication for severe eye, muscle or joint pain. If more serious symptoms or hemorrhagic fever develop, hospitalization is usually required for more aggressive administration of fluids and other supportive care measures. Prevention is the best medicine for dengue fever, which means avoiding mosquitoes. Recommendations include avoiding areas with standing water during the early morning and at dusk, when mosquitoes are most active; wearing protective clothing to prevent mosquito bites; and using insecticides and repellents as necessary.