Description
Glucose
This test is based on a sequential enzyme reaction. First, glucose oxidase catalyzes the formation of gluconic acid and hydrogen peroxide from the oxidation of glucose. A second enzyme, peroxidase, catalyzes the reaction of hydrogen peroxide with potassium iodide chromogen to oxidize the chromogen to colors ranging from blue through greenish-brown, and brown to dark-brown.
Reactivity of the test decreases as the specific gravity and/or pH of urine increases, and may also vary with temperature. Ascorbic acid (more than 50 mg/dl) and ketone bodies (more than 40 mg/dl) may cause a false negative result for a specimen containing a small amount of glucose (100 mg/dl). However, the combinations of such ketone levels and low glucose levels are metabolically improbable.
Protein
This test is based on the color change of the indicator tetrabromophenol blue. A positive reaction is indicated by a color change from yellow through green and then to greenish-blue.
The minimum sensitivity of this test is 10 mg/dl of protein in urine. Highly buffered alkaline urines (pH 9) may give false negative results. The interpretation of results is also difficult in turbid urine specimens.
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