Importance of the IgM/IgG index in dengue diagnostics (2023)

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 the IgM and IgG antibodies on the test helps doctors accurately diagnose dengue fever and treat it quickly and successfully.

1. Importance of IgM and IgG in dengue

Dengue usually shows a first sign of fever, which like other fevers is quite general, making it difficult to distinguish, so it is necessary to have specific tests and indicators to diagnose the disease.
IgM and IgG are two important indicators to assess dengue status. However, for more accurate results, the doctor will order a test that combines the dengue NS1 antigen with IgM and IgG antibodies, which also help to accurately detect the serotype caused by the dengue virus. The NS1 antigen and the IgM antibody help the doctor to correctly determine whether this patient's fever is caused by the dengue virus or not. In addition, IgG antibodies help determine whether the patient has already had such a fever in the near future. If the result shows that the IgG is positive, the patient has secondary dengue. Typically, NS1 antigens appear in the blood by days 1–9, IgM antibodies usually appear within 3–4 days, and IgG antibodies appear later, by day 14 after primary infection.

2. Diagnostic test for dengue

As one of acute-level infectious diseases that can form an epidemic of dengue virus, dengue fever starts when human is bitten by mosquitoes. Most tropical climates are ideal environments for the most rapid development of the disease. Vietnam typically experiences a hot season from July to October each year, when the risk of outbreaks is greatest.
Dengue initially has general clinical symptoms, so it is difficult to distinguish it from other fevers. In particular, there is no specific drug to treat the disease as well as prevent and treat the disease, so most doctors rely on test indicators to accurately diagnose whether the dengue virus has entered the human body or not.
In addition to the clinical signs of the disease, molecular biological tests and methods help to accurately and minimally identify the disease.
2.1 Analysis of the total leukocyte count in the blood: The number of white blood cells in the blood decreases in the presence of dengue virus. Once dengue is ruled out, white blood cell and neutrophil counts increase again. Platelets: The risk of bleeding increases when the number of platelets falls sharply. Dengue virus occurs, causing platelet counts to drop and can fall below 100 Giga/L. Hematocrit: The hematocrit increases by 20% and exceeds the patient's normal threshold. Note that when the blood has a condensed phenomenon, the index is greater than 45%. 2.2 Biomolecular tests If the antibody detection rate is slower, the presence of dengue RNA virus in the blood can be determined from the first few days when dengue shows no clinical signs. special sieve. Most of these tests are available in places with modern and adequate equipment.
2.3 Immunoassays Immunoassays help to detect dengue NS1 antigens and IgM, anti-dengue IgM and IgG, anti-dengue IgG antibodies. The index test can be late in detecting the presence of antibodies because they usually appear after the primary dengue infection.
Quantification of Dengue IgM Antibodies: The IgM index appears slowly at the time of primary dengue fever, most patients can be detected within 3 to 4 days after the time of fever. Dengue IgM persists in the blood for up to about 90 days. Quantification of Dengue IgG Antibodies: Initially, Dengue IgG is almost not seen in the acute phase, only when the body recovers. Until the secondary moment, dengue IgG is present from the acute moment and will show a 4-fold increase compared to before at the moment of recovery, usually by day 14 after the moment of primary infection. Possible tests:
NS1-Antigentest
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
Combined IgM and IgG test or NS1 rapid test with IgM and IgG ELISA Anti-Dengue IgM test ELISA Anti-Dengue IgG test ELISA Anti-Dengue IgM, IgG test The rapid tests help and enable earlier and more accurate diagnosis of dengue fever virus. The rapid test provides results with a sensitivity of up to 92% and a specificity of 75 to 95%.

3. How to read dengue results

Phase 1: Day 1-5 immediately after the fever period
Dengue NS1 index positive, IgM negative, IgG negative, Dengue RNA negative => primary dengue virus fever, early stage disease state. Dengue NS1 index positive, IgM negative, IgG negative, Dengue RNA positive => primary dengue virus fever, disease status in the acute phase. Dengue NS1 index positive, IgM positive, IgG negative, Dengue RNA positive => primary dengue virus fever, disease state in the acute stage. Dengue NS1 index positive, IgM negative, IgG positive, Dengue RNA positive => secondary dengue virus fever, disease state in the acute stage. Dengue NS1 index positive, IgM positive, IgG positive, Dengue RNA positive => secondary dengue virus fever, acute stage disease state. For all tests, days 3 and 4 are the times when the highest rate of viral infection is detected, days 5 and 6 can detect a higher proportion of antibodies than antigens.
Phase 2: Days 6-9 right after the fever period
Dengue NS1 index positive, IgM positive, IgG negative, Dengue RNA positive => primary dengue virus fever, disease state in the acute stage. Dengue NS1 index positive, IgM positive, IgG positive, Dengue RNA positive => secondary dengue virus fever, acute stage disease state. Stage 3: From the 9th day after the fever phase
All tests show a decrease, the diagnostic significance decreases, the positivity rate drops to only 0.8 to 1.6%.
With the global blood analysis test: it can reduce the number of white blood cells in the blood, the number of platelets decreases, causing risks of bleeding, the amount of plasma leaking causes a concentration in the blood, the appearance of small blood spots under the skin.
Dengue is a disease for which there is no specific treatment or preventive medicine. So by ensuring accurate diagnostic test results for IgM and IgG antibodies, you can treat the disease and recover quickly.
Vinmec International General Hospital is one of the hospitals that not only guarantees professional quality with a team of top doctors, modern equipment and technology, but also stands out for its examination and consultation services. comprehensive and professional medical advice and treatment; civilized, polite, safe and sterile examination and treatment room. Customers who choose to test here can be absolutely confident in the accuracy of their test results.

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