Increased speed and sensitivity, and reduced sample size of a micro-radioallergosorbent test (MRAST).

Performance of the radioallergosorbent test (RAST) in small volumes (MRAST) increases the efficiency with which both IgE antibody and 125I-anti-IgE bind. The rate at which antibody binds is increased up to 290-fold so that the assay can be completed in 60 min with comparable sensitivity to RAST. The increased speed of binding is achieved by the use of small incubation volumes which does not affect the rate at which bound antibody is dissociated. The resulting change in the equilibrium in favour of antibody binding yields a 10-fold increase in sensitivity which makes it possible to use as little as 5 microliter of sample compared with 50 microliter which is normal for RAST. MRAST can be used to measure IgE antibody in heel prick blood samples taken from babies, in rat sera and in other situations where the sample is in short supply.