Evolution of an inhibin A ELISA method: Implications for Down's syndrome screening

The development of a sensitive and specific enzyme-linked immuno-assay (ELISA) for inhibin A stimulated the observation that inhibin A was a useful prenatal marker of Down's syndrome. Modifications of that ELISA, in terms of pre-assay sample treatment, detection methods and standard preparation, were subsequently introduced to improve assay performance and reduce costs. These modified formats have been validated and reported. We describe the modifications in detail, explaining the rationale for each, and report the results of a study directly comparing the various ELISA formats in terms of assay performance when applied to clinical samples and ability to differentiate between normal and Down's syndrome pregnancies. A format involving sample pretreatment with sodium dodecylsulphate at 100°C was found to give better assay performance and a modest improvement in discrimination between Down's syndrome samples and controls, and we recommend this format for use by other investigators.