Case Study: Dark Urine after Strep Throat Answers


2. In general, the other chemical tests that are affected by the ascorbic acid increase are glucose, bilirubin, and nitrite.  Ascorbic acid will cause a false decrease in each of the four tests on the chemical stix.  The methods are described below:

*In the methods presented below, the oxidized chromagen is the colored end product that produces a color on the pad while oxidized ascorbic acid is colorless.

Blood: *heme has a pseudoperoxidase activity
Normal:
                                                                     heme
Hydrogen peroxide + reduced chromagen ------------------->  oxidized chromagen + water

Ascorbic Acid Interference:
                                                                       heme
Hydrogen peroxide + reduced ascorbic acid ------------------->  oxidized ascorbic acid + water  
                           AND

                                                                     heme
Hydrogen peroxide + reduced chromagen ------------------->  decreased oxidized chromagen + water

Glucose:
Normal:          glucose oxidase
Glucose + O2 ------------------------> gluconic acid + hydrogen peroxide 
                                                                 peroxidase
Hydrogen peroxide + reduced chromagen ------------------->  oxidized chromagen + water

Ascorbic Acid Interference:
                       glucose oxidase
Glucose + O2 ------------------------> gluconic acid + hydrogen peroxide 
                                                                    peroxidase
Hydrogen peroxide + reduced ascorbic acid ------------------->  oxidized ascorbic acid + water  
                           AND

                                                                 peroxidase
Hydrogen peroxide + reduced chromagen ------------------->  decreased oxidized chromagen + water

Bilirubin:
Normal:
                                                                            acid pH
Bilirubin glucuronide + diazonium salt (colorless) ------------> azobilirubin (colored)

Ascorbic Acid Interference:
                                                                             acid pH
Bilirubin glucuronide + diazomium salt (colorless) ------------> decreased azobilirubin (colored)

                         AND
                                                                acid pH
Ascorbic acid + diazonium salt (colorless) ------------> colorless end product

Nitrite:
Normal:
                                       acid pH
Aromatic amine + nitrite ------------> diazonium salt
Diazonium salt + aromatic compound -------> pink color

Ascorbic Acid Interference:
                                         acid pH
Aromatic amine + nitrite --------------> diazonium salt
Aromatic compound + diazomium salt (colorless) ------------> decreased pink color

                         AND
                                                               
Ascorbic acid + diazonium salt (colorless) ------------> colorless end product


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