Anti-dsDNA antibodies were the first autoantibodies described in patients with SLE. Anti-dsDNA antibodies can be found in up to 70% to 80% of patients with SLE at some time during the course of the disease, these antibodies are very rarely found in patients with other autoimmune conditions and in healthy controls. Furthermore, in many cases there is a relationship between disease activity and the titer of anti-dsDNA. In a larger study, Swaak showed that rise in levels of anti-dsDNA antibodies preceded renal flares in SLE (3) and subsequent independent studies also showed that rises in anti-ds DNA antibody level were associated with flares of activity, either in the kidney or in other organ.

The autoantibodies are present in 50% of patients with SLE and 1-5% of the general population. The antiphospholipid antibodies are found in serum in 1% of healthy persons and 3% of older age group (2). Though APS can involve any age group, the target group is young to middle aged adults. Depending upon the site of vascular obstruction, various symptoms occur in patients with APS. Interference in the balance between procoagulant and anticoagulant factors and disruption of the clotting mechanism by the antiphospholipid antibodies (APLA) lead to leg ulcers, toe gangrene, myocardial infarction, purpura, stroke, recurrent miscarriage or preterm births.

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Introduction: Dengue is a viral infection with diverse clinical manifestations. Infection in most of the patients is subclinical. It may also present as undifferentiated fever, severe dengue like Dengue Haemorrhagic Fever (DHF) and Dengue Shock Syndrome (DSS). Secondary dengue infection predisposes to severe dengue, a serious threat to the community as they increase morbidities and mortality. The diagnosis of secondary infection is either by Polymerase Chain Reaction (PCR) to detect the serotype or dengue IgG/IgM antibody ratio. A ratio of more than 1.1 is evidence of secondary dengue. Aim: To find out the prevalence of secondary dengue by measuring the dengue anti-IgG/IgM ratio by Enzyme Linked Immunosorbent Assay (ELISA) test. Materials and Methods: This cross-sectional observational study was conducted at Government Kilpauk Medical College, Chennai for a period of six months from July 2021 to December 2021. Sample size was 450 calculated at 95% confidence level, (CI 28.3-38.3) with 33.3% as prevalence. Blood samples were collected and Nonstructural Protein 1 (NS1) antigen assay was done. The IgG and IgM antibodies assays were done for NS1 antigen positive individuals. The IgG/IgM ratio was calculated in patients who were positive for both IgG and IgM. Statistical analysis was done with Statistical Package for Social Sciences (SPSS) version 20.0. Percentage, mean and standard deviation were calculated. Results: Total of 450 patients were included, out of which 194 were NS1 antigen positive, 106 were males and 88 females with the mean age 25±14.85 years. NS1 antigen was positive in 89.17%. Two-tailed Fisher’s-exact test showed a significant proportion of patients among NS1 positive were positive for both IgG and IgM. An IgG/IgM ratio of >1.1 was found in 62.04%. The association between IgG/IgM ratio of >1.1 and thrombocytopenia was significant [p-value=0.00504, Odd’s ratio (OD) =3.316]. Conclusion: Dengue IgG/IgM antibody ratio of more than 1.1 on the third day of symptom onset and the platelet count assist in the early diagnosis of secondary dengue thereby helps clinicians to initiate the appropriate treatment at the right time, reduce mortality rate and decrease the economic burden of the country.