ferrocyanide ferricyanide system it will be understood that the criteria which the control reagent must satisfy are independent of the actual test system thus the control reagent will be seen to be useful in connection with any of the known glucose analysis systems essential to the invention are a predetermined amount glucose water and the recited polystyrene sulphonate the water is used of course to create a reagent solution by 34 predetermined 34 is meant that prior to formulation of the actual reagent a concentration of glucose has been selected this concentration may vary as those skilled in the art will recognize as has been mentioned supra the art recognizes e g a range of from 40 to 500 mg dl but one may envision lower ranges to e g about 20 mg dl some typical ranges would be from about 60 to about 240 mg dl or from about 60 to about 300 mg dl the essential features of the invention when the reagent is in the form of a solution are the solvent water the predetermined amount of glucose and the polystyrene sulphonate or a salt thereof the polystyrene sulphonate or its salt may be present in e g from about 0 5 to about 55 60 weight percent of the reagent a preferred range is from about 0 5 to about 40 weight percent of the control reagent in an especially preferred embodiment a range of from about 20 to 30 weight percent is used the weight percent of the polymer will vary depending upon factors which include molecular weight and solubility the.