Use of dried blood blotted on filter paper to detect dengue IgM antibody and dengue NS1 antigen.

A cross sectional study was conducted at the Department of Microbiology, Maulana Azad Medical College, New Delhi, to determine the efficacy of capillary blood samples collected on filter paper compared with serum samples to detect dengue IgM antibody and dengue NS1 antigen. The serum and capillary blood samples were collected from 104 suspected cases of dengue fever at Lok Nayak Hospital, India. The blood eluted from the filter paper and the serum samples were tested for dengue IgM antibody and dengue NS1 antigen by commercial capture ELISA kits. Of the 104 patients, samples from 61 patients tested positive for dengue IgM antibodies with both the serum and filter paper. Samples from 38 patients were negative for both serum and filter paper. Five samples showed discordant results. The filter paper method had sensitivity of 96.8% and specificity of 97.4% for dengue IgM antibody compared to the serum samples. The positive predictive value (PPV) and negative predictive value (NPV) for the filter paper to detect dengue IgM were 95.31% and 95.0%, respectively. The Kappa value (>0.80) showed agreement between the filter paper and serum results for IgM antibody detection. NS1 antigen was detected 28 serum and 28 filter paper samples and was not detected in 72 serum and 72 filter paper samples. Discordant results were seen in 4 samples. The filter paper method had a sensitivity of 96.5% and a specificity of 96.0% compared to the serum for detecting dengue NS1 antigen. The PPV and NPV for the filter paper samples in detecting dengue NS1 antigen were 90.3% and 98.7%, respectively. The Kappa value showed agreement (>0.80) between the serum and filter paper results for detecting dengue NS1 antigen. The results show filter paper samples are a reasonable alternative to serum for detecting dengue infecting.