Diagnosis of Dengue Fever: The diagnosis for dengue is made based on the symptoms presented by the person, in addition to laboratory tests, such as a blood count, virus isolation and biochemical tests, for example. From the realization of the examinations, the doctor can verify what is the type of virus and, in this way, indicate the most appropriate treatment for the person. Thus, in the event that fever arises accompanied by two or more symptoms of those referred to above, it is recommended to go to the emergency department for diagnostic tests, and thus, start treatment.
Dengue is a disease caused by the bite of the infected Aedes aegypti mosquito, which is more common to occur in summer and in more humid areas due to the ease of dengue mosquito development. Learn how to identify and fight the dengue mosquito.
1. Physical exam
The physical examination consists of the evaluation by the doctor of the symptoms described by the patient, the following being an indicator of classic dengue:
In the case of hemorrhagic dengue, symptoms may include excessive bleeding that usually manifests with red spots on the skin, frequent bruising and bleeding of the nose or gums for example.
Symptoms usually arise 4 to 7 days after the bite of the virus-infected mosquito and start with a fever above 39º C, but after a few hours, it is accompanied by other symptoms. Therefore, if blood is suspected, it is important to seek medical help to perform specific tests to confirm the diagnosis and start treatment as quickly as possible, since in the most severe cases the dengue virus can affect the liver and the heart. Learn more about the complications of dengue.
The tourniquet test is a type of test that verifies the fragility of blood vessels and their tendency to bleed, is often performed in cases of suspected classic dengue or hemorrhage. This test consists of interrupting the blood flow in the arm and observing the appearance of small red dots, with more risk of bleeding while more red spots are observed.
Although it is part of the tests indicated by the World Health Organization for the diagnosis of dengue, the tourniquet test can give false results when the person is taking medications such as aspirin or corticosteroids or is in the pre or postmenopausal phase, for example.
The rapid test to identify dengue is increasingly being used to diagnose possible causes of virus infection, since it takes at least 20 minutes to identify if the virus is present in the body and how long due to antibody detection, IgG and IgM. In this way, it is possible to start the treatment faster.
However, the rapid test does not identify the presence of other diseases transmitted by the dengue mosquito, such as Zika or Chikungunya, so the doctor can ask for a normal blood test to identify if you are also being infected by these viruses. The rapid test is usually free, depending on the country and health standards, and can be found in health centers. It can be done at any time since no pre-test preparation is necessary.
This test aims to identify the virus in the bloodstream and establish its serotype, allowing differential diagnosis of other diseases caused by the same mosquito bite and that present with similar symptoms, in addition to allowing the doctor to initiate a more specific treatment.
Isolation is done by analyzing a blood sample, which must be obtained once the first symptoms arise. This blood sample is sent to the laboratory and, through molecular diagnostic techniques, such as PCR, for example, it is possible to identify the presence of dengue virus in the blood.
Serological tests are aimed at diagnosing the disease through the concentration of IgM and IgG immunoglobulins in the blood, which are proteins that are altered in their concentration in cases of infection.
The concentration of IgM increases after contact of the person with the virus, while IgG increases later, but in the acute phase of the disease, it remains in high amounts in the blood, thus being a marker of disease, since It is specific for each type of infection. Learn more about IgM and IgG antibodies.
Serological tests are usually requested as a way to complement the virus isolation test and the blood must be obtained about 6 days after the symptoms occur, since it is thus possible to verify more correctly the immunoglobulin concentrations.
The blood count and correlogram are also tests requested by the doctor to diagnose dengue, mainly hemorrhagic dengue. In the blood count, the variable amounts of leukocytes are usually verified, and there may be leukocytosis, which is the increase in the number of leukocytes, or leukopenia, which is the decrease in the number of leukocytes in the blood.
In addition, the increase in the number of lymphocytes (lymphocytosis) is usually observed with the presence of atypical lymphocytes, in addition to thrombocytopenia, which is when platelets are below 100,000 / mm³ when the reference value is between 150,000 and 450,000 / mm³. Know the normal blood count values.
The correlogram, is the test that verifies the blood’s clotting ability, is usually requested in case of suspicion of hemorrhagic dengue and increased prothrombin time, partial thromboplastin and thrombin can be observed, in addition to the decrease in fibrinogen, prothrombin, factor VIII and factor XII, confirming the diagnosis of hemorrhagic dengue.
The main biochemical tests requested are the measurement of albumin and liver enzymes TGO and TGP, indicating the degree of liver involvement and being an indicator of the most advanced state of the disease when these parameters are elevated.
Normally when dengue is in a more advanced stage it is possible to observe the decrease in the concentration of albumin in the blood and the presence of albumin in the urine, in addition to the increase in the concentrations of TGO and TGP in the blood, indicating liver damage.