The Hook Effect

The hook effect

When a negative is not a negative: The mystery about false test strip results.

Overloading a lateral flow device with allergen can lead to a false negative result. This process is referred to as the “hook effect”.

The hook effect does not pose a problem in day-to-day testing using the strips. In fact, it is only usually encountered when someone is trying to verify if the LFDs are working correctly by testing 100% of the allergenic food. By doing so, the amount of allergen present exceeds the finite amount of the colored labelling material, often colloidal gold or colored latex coupled to the detection antibody. 

The excess unlabelled allergen migrates along the membrane quicker than the heavier color-labelled allergen, saturating all the binding sites on the capture antibodies immobilised on the membrane surface. When the color-labelled allergen arrives, no binding sites remain, so it simply continues on to the wicking pad at the end of the test device. Since no binding sites were available, the color-labelled allergen cannot create the colored test line that would normally represent a positive result.