In Benedict's test which of the end color indicates absence of sugar in urine?

Appeared in: BHU NO - 2015

Explanation

Benedict's test is a chemical assay used to detect the presence of reducing sugars.
The reagent used in the test, Benedict's solution, is initially blue due to the presence of copper(II) sulfate.
If no reducing sugars are present in the sample (e.g., urine), no chemical reaction occurs upon heating.
Consequently, the solution remains its original blue color, which indicates a negative result and the absence of sugar.

Option A: A yellow color indicates a positive result, signifying the presence of a low to moderate concentration of reducing sugars, typically around 1.0-1.5 g%.
Option B: A green color or precipitate is also a positive result, indicating a trace amount of reducing sugar, approximately 0.5-1.0 g%.
Option C: An orange color is a positive result that indicates a moderate to high concentration of reducing sugars, generally in the range of 1.5-2.0 g%.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Interpretation of Benedict's test results for urinalysis as background academic context rather than a clinical decision trigger.
This is a fundamental bedside test for screening for glycosuria (sugar in urine), which is a hallmark sign of conditions like diabetes mellitus.
A nurse must be able to accurately interpret the color change to report the semi-quantitative result, which aids in monitoring a patient's glucose levels and the effectiveness of treatment.
While modern practice often uses more specific glucose oxidase dipsticks, Benedict's test is still relevant in some settings and for detecting other reducing substances.

How to Approach the Question

First, identify the core of the question: what color means 'absence of sugar' in Benedict's test.
Recall the starting color of the Benedict's reagent, which is blue due to its copper sulfate content.
Understand the principle: a positive test involves a chemical reaction that changes the color of the reagent. The colors green, yellow, orange, and red all represent a positive result with increasing sugar concentration.
Therefore, if no reaction occurs (due to the absence of sugar), the reagent's color will not change.
Evaluate the options. Green, yellow, and orange are all colors indicating a positive reaction.
Conclude that the original blue color is the only option that indicates a negative test.

Concept Tested & Keywords

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E6 Pathology-Vandana Puri & Kavita Gaur Textbook of Pathology and Genetics p. 449-451

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