Urinalysis and Body Fluids 6th Edition by Majorie DiLorenzo, Susan Strasinger

Exercise 21

The principle of the reagent strip test for pH is the:

A. Protein error of indicators

B. Greiss reaction

C. Dissociation of a polyelectrolyte

D. Double indicator reaction

Step 1 of 2

Reagent strip reactions:

Reagent strips are used in a laboratory for chemical analysis.

• To carry out the reaction in reagent strips, certain indicators detect certain elements in urine.

Indicator:

Indicators are chemicals used in reagent strips for detecting elements. For example: methyl orange, methylene blue, etc…

• The reagent strips brands “chemstrip” and “multistix” for detecting urine pH, use two indicators namely; bromthymol blue and methyl red. This is called double indicator reaction.

o Methyl red gives change of color from red -> yellow in the pH 4-6.

o Bromthymol blue gives color change from yellow -> blue in the pH 6-9.

• So, color change from orange ->yellow->green->deep blue appears from the pH 5-9.

Therefore, the pH test in reagent strip principle is “double indicator reaction”. Hence, the correct answer is option .