Progesterone Test Kit -
Example of a Competetive Immunoassay

Key to Shapes:
Unlabeled antibody to progesterone (yellow)		Progesterone hormone present in serum in certain stages of estrus or pregnancy (green)		Enzyme-labeled progesterone (pink)

Outline of Kit:
1. Blood serum sample is added to test cup. Progesterone in the sample will bind to antibodies attached to the bottom of the cup or well.
High-Progesterone Sample	Intermediate-Progesterone Sample	Low-Progesterone Sample
2. Enzyme-labeled progesterone is added to the cup. If the serum sample contains high levels of progesterone, all of the antibody binding sites will be occupied, there will be no place for the labeled progesterone to bind, and it will be washed away. If there was little or no progesterone in the sample, there will be available antibody binding sites for the labeled progesterone and it will be held in the well.
High-Progesterone Sample	Intermediate-Progesterone Sample	Low-Progesterone Sample
3. Color-producing substrate for the enzyme is added to the well. The amount of color produced will correspond to the amount of labeled progesterone bound to the well, which is inversely correlated to the amount of progesterone in the sample.
High-Progesterone Sample Result: NO COLOR	Intermediate-Progesterone Sample Result: LIGHT BLUE	Low-Progesterone Sample Result: BRIGHT BLUE