Significance of IgM/IgG index in dengue fever diagnostic test

This is an automatically translated article.

The article is professionally consulted by MSc Nguyen Thi Ngoc - General Doctor, General Health Examination Unit, Vinmec Central Park International General Hospital.
Understanding and accurately reading IgM and IgG antibodies in the test will help doctors diagnose dengue accurately and treat it quickly and successfully.

1. Significance of IgM and IgG in Dengue fever

Dengue fever will often have a fairly general initial sign of fever like other fevers, so it will be difficult to distinguish, so it is necessary to rely on tests and specific indicators to diagnose the disease.
IgM and IgG are two important indicators in assessing the status of dengue fever. However, for the most accurate results, the doctor will order a test that combines Dengue NS1 antigen with IgM and IgG antibodies, which also supports the accurate detection of the serotype caused by Dengue virus. NS1 antigen and IgM antibody will help the doctor to correctly determine if this patient's fever is caused by dengue virus or not. In addition, IgG antibodies will help determine if the patient has ever had such a fever in the near future. If the result shows that IgG is positive, then the patient is experiencing secondary dengue fever. Usually NS1 antigens will appear in the blood on day 1-9, IgM antibodies will usually appear on 3-4 days and IgG antibodies will appear later on day 14 after the time of primary infection.

2. Diagnostic test for dengue fever

As one of the infectious diseases at an acute level, which can form an epidemic of Dengue virus, dengue fever begins when humans are bitten by mosquitoes. Most of the tropical climates are the ideal environment for the fastest disease development. Every year, Vietnam often has a hot season from July to October, which is the time when the risk of outbreaks is greatest.
Dengue fever initially with general clinical signs, so it is difficult to distinguish from other fevers. Especially, there is no specific medicine to treat the disease as well as prevent and treat the disease, so most doctors will rely on test indicators to accurately diagnose whether Dengue virus has entered the human body or not.
In addition to the clinical signs of the disease, tests and molecular biology methods help to detect the disease accurately and at the earliest.
2.1 Analysis of the total blood Leukocytes : the number of white blood cells in the blood will decrease in the presence of dengue virus. Once Dengue is ruled out, the white blood cell count and neutrophil count will increase again. Platelets: The risk of bleeding increases when the number of platelets drops sharply. Dengue virus appears, causing the platelet count to drop, which can fall below 100 Giga/L. Hematocrit: the hematocrit will increase by 20%, exceeding the normal threshold of the patient. Note that the index exceeding 45% is when the blood has a condensed phenomenon. 2.2 Biomolecular testing When the detection index of antibodies is slower, the presence of RNA-Dengue virus in the blood can be determined from the first days when dengue fever has not shown any clinical signs. specific sieve. Most of these tests are available in places with modern and adequate equipment.
2.3 Immunoassays Immunoassays help detect Dengue NS1 antigens and IgM, anti Dengue IgM antibodies and IgG, anti Dengue IgG antibodies. The index test can detect the presence of antibodies late because they often appear after the primary dengue infection.
Quantification of Dengue IgM antibodies: IgM index is slow to appear at the time of primary Dengue, most patients can be detected at 3 - 4 days from the time of fever. Dengue IgM lasts up to about 90 days in the blood. Quantification of Dengue IgG antibodies: in the primary time, Dengue IgG is almost not seen in the acute phase, but only when the body enters recovery. Up to the secondary time, Dengue IgG is present right from the acute time and will have an increase of 4 times compared to before, right at the time of recovery, usually on day 14 after the time of primary infection. Possible tests:
NS1 antigen test
Dengue NS1 rapid test (can combine NS1 test with IgG and IgM test) Dengue NS1 ELISA test IgM/anti IgM and IgG/anti IgG test
Combination test IgM and IgG, or rapid test NS1 with IgM and IgG Test ELISA anti Dengue IgM Test ELISA anti Dengue IgG Test ELISA anti Dengue IgM,IgG Rapid tests support and screen for the earliest and accurate diagnosis of the presence of dengue virus. The rapid test yields results with a sensitivity of up to 92%, and a specificity of 75 to 95%.

3. How to read dengue fever results

Stage 1: Day 1-5 immediately after the time of fever
Dengue NS1 index positive, IgM negative, IgG negative, Dengue RNA negative => primary dengue virus fever, disease condition in early stage. Dengue NS1 index positive, IgM negative, IgG negative, Dengue RNA positive => primary dengue virus fever, disease state in the acute stage. Dengue NS1 index positive, IgM positive, IgG negative, Dengue RNA positive => primary dengue virus fever, disease state in acute stage. Dengue NS1 index positive, IgM negative, IgG positive, Dengue RNA positive => secondary dengue virus fever, disease state in acute stage. Dengue NS1 index positive, IgM positive, IgG positive, Dengue RNA positive => secondary dengue virus fever, disease state in acute stage. In all tests, days 3 and 4 are the time to detect the highest rate of viral infection, days 5 and 6 can detect a higher proportion of antibodies than antigens.
Stage 2: Days 6-9 right after the time of fever
Dengue NS1 index positive, IgM positive, IgG negative, Dengue RNA positive => primary dengue virus fever, disease state in acute stage . Dengue NS1 index positive, IgM positive, IgG positive, Dengue RNA positive => secondary dengue virus fever, disease state in acute stage. Stage 3: From day 9 after the time of fever
All tests show a decrease, the diagnostic value decreases, the positive index falls to only 0.8 to 1.6%.
With the overall blood analysis test: can reduce the number of white blood cells in the blood, the number of platelets decreases, causing the risk of bleeding, the amount of plasma escaping causes concentration in the blood, the appearance of small blood spots under the skin.
Dengue fever is a disease that has no specific treatment as well as preventive medicine, therefore, ensuring accurate diagnostic test results for IgM and IgG antibodies will help treat the disease quickly and recover.
Vinmec International General Hospital is one of the hospitals that not only ensures professional quality with a team of leading medical doctors, modern equipment and technology, but also stands out for its examination and consultation services. comprehensive and professional medical consultation and treatment; civilized, polite, safe and sterile medical examination and treatment space. Customers when choosing to perform tests here can be completely assured of the accuracy of test results.

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