A comparison of assay methods for pregnancy specific beta 1 glycoprotein (SP-1).

Three methods were compared for the assay of pregnancy specific beta 1 glycoprotein (SP-1): radical immunodiffusion (RID), electroimmunodiffusion (EID) and radioimmunoassay (RIA). There was a significant correlation between EID and RIA. A lower, but still significant correlation was found between EID and RID, but wide discrepancies were seen in some cases. This finding suggests heterogeneity of SP-1 molecule(s). The data indicate that EID is the method of choice for assay of SP-1 after the tenth week of pregnancy, while the more sensitive RIA should be reserved for use before that stage.