Equipment for homogeneous enzyme immunoassays

Results of EIA may be given in two forms (i) expressing the activity of the antiserum in some arbitrary or relative units and, (ii) expressing the concentration of the antigen or hapten (often in mg/ml). 

The frequent homogeneity of haptens or antigens contrasts with the heterogeneity in affinity and concentration of antibodies in the antisera and results in fundamental differences in the nature of the dose-response relations for antibodies and for antigens. 

An essential element in quantitative assays is the setting of the positive/negative discrimination level (eut-off value). The term negative is used as indicating the absence of specific antibodies or antigens above the background noise. 

Various mathematical models can improve the precision of curve fitting, particularly for hapten dose-response curves, to obtain accurate results with less data required for the standard curve, saving both time and cost. This is particularly valid in situations where programmable caleulators or microcomputers can be interfaced with microplate readers and printers. 

The general use of standard deviation (SD) is, strictly speaking, not valid since EIA values for negative reference sera are distributed 

---