I've been detecting the presence of an enzyme in plasma using an adapted ELISA protocol with a positive control from pooled patient samples. The assay works great and I've got some good results however I would like some help in interpreting them and scoring them in effect. I presume that you go off the titre or end point i.e. how many times the sample is diluted before the 'signal' or colour disappears. So I have the end point for the positive control and then end point for an unkown sample but when can I say for instance that a sample is negative or positive for the enzyme? Do you compare the titres of the control and sample directly to produce a ratio or is there a sort of 'standard' titre which you say make the sample positive for your protein??
Any help would be most gratefully received.