Fig. 3.

Illustration of the high dose hook effect. The left panel illustrates the non-competitive “sandwich” immunoassay with normal (or elevated within the tolerance of the assay kit) hormone concentration (see Fig. 2). The right panel illustrates the mechanism of the hook effect with exceedingly high hormone concentration. a The sample that contains remarkably elevated hormone concentration is added to the test tube which contains both capture and signal antibodies. b The studied hormone overwhelmingly saturates both the capture and signal antibodies preventing the formation of the “sandwiches”. c After the washout phase, only a few “sandwiches” will be left producing a low signal