a substituted or unsubstituted c 1 c 4 alkyl alkoxy or halogen with the proviso that r 1 r 2 and r 3 cannot simultaneously be hydrogen the indoles are dissolved in a nonionic detergent to produce an indole solution which can be up to 10 percent w w indole although the indoles which are suitable for use in the present invention are relatively insoluble in water the indole detergent solutions formed are easily solubilized in water the indole detergent solution can then be further diluted e g to 1 percent 0 1 percent and 0 01 percent for use as a control standard the control standards thus prepared simulate a urobilinogen concentration range of from about 2 to about 12 ehrlich units it has been determined that suitable nonionic detergents for use in the present invention are alkanolamides ethoxy alkanolamides ethoxy phenols and ethoxy fatty alcohols liquid preparations are preferably incorporated with a carrier matrix in strip format the term carrier matrix can be envisioned to refer to bibulous and nonbibulous matrices which are insoluble in and maintain their structural integrity when exposed to water or physiological fluids suitable bibulous matrices which can be used include paper cellulose wood synthetic resin fleeces woven and nonwoven fabrics and the like nonbibulous matrices include organoplastic materials such.