The alkaline saline solution is used in staining kits, such as the Congo red according to Puchtler, as an additive to the Congo red solution. It contains sodium hydroxide and sodium chloride in aqueous alcoholic solution and is used to increase the pH of the Congo red solution, thereby optimizing the staining reaction.

Congo red, an anion dye, binds more efficiently to proteins when the medium is alkaline. Addition of the alkaline saline solution achieves this condition.

In addition, the sodium chloride in the solution increases ionic strength, resulting in improved staining intensity and quality.

The combination of Congo red solution with alkaline saline thus enables precise and reliable staining results in in vitro diagnostics, facilitating the correct identification and classification of cells and tissues.