ELISA Detects Measles-Specific IgG In Dried Blood Spots

A novel technique for measuring measles-specific immunoglobulin G (IgG) in capillary dried blood spots (DBS) using a commercial enzyme-linked immunosorbent assay (ELISA) has been validated.

There are many poor, remote areas in Mesoamerica where little is known about population immunity to measles but this data can be significantly enhanced by measuring anti-measles antibody titers, preferably using DBS which are minimally invasive and affordable.

Scientists at the University of Washington (Seattle, WA, USA) working with their colleagues from Mexico, Panama and Nicaragua, tested a new method for analyzing DBS by comparing matched serum and DBS samples from 50 children. The accuracy, precision, and reliability of the procedure were evaluated, and the optimal cut points to classify positive and negative samples were determined. The method was then applied to 1,588 DBS collected during a large survey of children in Mexico and Nicaragua.

Serum samples were assayed for the presence of measles-specific IgG antibodies (family Paramyxoviridae, genus Morbillivirus, species Measles virus) using the HUMAN Worldwide Diagnostics Measles IgG ELISA kit (Wiesbaden, Germany). The plates were processed through a series of incubation, wash, and reaction steps, ultimately resulting in a color change. The degree of color development of each well, which is directly proportional to the measles IgG antibody concentration in the specimen, was measured spectrophotometrically on a Multiskan MS plate reader (Labsystems Diagnostics; Helsinki, Finland).

Measles-specific IgG in serum samples were 62% negative, 10% equivocal and 28% positive. In comparisons with matched serum, DBS results were 100% sensitive and 96.8% specific, and agreed in 46 of 50 (92%) cases. The seroprevalence of measles-specific IgG in the field study was 63.4% in Mexico and 50.7% in Nicaragua. The inter-assay and intra-assay coefficients of variation from kit-provided controls were greater than desired at 24.8% and 8.4%, respectively; however, in predictive simulations the average misclassification was only 3.9%.

The authors concluded that their study establishes that the applied commercial ELISA test can be used to categorize individuals as having measles-specific IgG through analyses of DBS. In support of this contention, this study found that measles-specific IgG values in DBS and matched serum samples were strongly linearly related, highly correlated, and nearly directly equal. Analyzing DBS collected in low-resources settings is a feasible and accurate means of measuring population immunity to measles and should be used to generate objective measures of health status and health system performance. The study was published in the September 2015 issue of the Journal of Medical Virology.

Related Links:
University of Washington 
HUMAN Worldwide Diagnostics 
Labsystems Diagnostics