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

Exercise 20

Explain the “protein error of indicators,” and list any sources of interference that may occur with this method of protein testing.

Step 1 of 2

Protein error of indicators:

It is a tradition method of testing protein in reagent strips.

• Protein error of indicators principle is colorimetric reaction.

• Normally in response to specific pH range, indicators produces particular color, in contrary to this, in the constant pH also, indicators change color when protein exist.

o This is due to albumin (protein) which accepts hydrogen ion from indicator.

• More amino groups are available in albumin for accepting the hydrogen ions compared to other protein.

• Multistix brand uses tetrabromophenol blue or tetrachlorophenol, and chemstrip brand uses tetrabromosulfonphthalein.

• Acid buffer is placed on reagent strips to maintain pH.

• At pH 3, both of the indicators give yellow color in protein absence.

• When concentration of protein increases color change from green ---> blue appears.

• Results are reported as negative or trace or 1+, 2+, 3+ and 4+ (or) 2000, 300, 100 and 30 mg/dL (Milli grams per deciliter).