Which of the following substances in urine will give a positive reaction with Benedict's test?

Appeared in: RML 2023

Explanation

Benedict's test is specifically designed to detect reducing sugars, which have a free aldehyde or ketone functional group.
Glucose is a monosaccharide and a classic example of a reducing sugar.
When heated with Benedict's reagent, glucose reduces the blue cupric sulfate (Cu²⁺) to a brick-red cuprous oxide (Cu₂O) precipitate.
The intensity of the color change, from green to yellow to orange to red, provides a semi-quantitative estimate of the glucose concentration.

Option A: Acetone is a ketone body, not a reducing sugar. Its presence in urine indicates ketonuria, often associated with uncontrolled diabetes or starvation.
Option C: Bile salts are steroids, not reducing sugars. Their presence in urine is detected by Hay's test, which relies on the principle of altered surface tension.
Option D: Albumin is a protein. Its presence in urine (proteinuria) is a sign of kidney damage and is detected by tests like the heat coagulation test or sulfosalicylic acid test, not Benedict's test.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Urine analysis for reducing sugars using Benedict's test as background academic context rather than a clinical decision trigger.
Screening for glucose in urine (glycosuria) is a fundamental nursing assessment, often indicating hyperglycemia and prompting further investigation for diabetes mellitus.
Nurses must ensure proper urine sample collection (e.g., clean-catch midstream) and accurate test performance and interpretation to avoid false results.
What if? A patient's urine is positive with Benedict's test but negative with a glucose-oxidase strip test. This suggests the presence of a non-glucose reducing substance (e.g., fructose, lactose, or certain medications like high-dose Vitamin C), which requires notifying the physician for further evaluation.

How to Approach the Question

This is a factual recall question about a common laboratory procedure.
First, identify the key term in the question: 'Benedict's test'.
Recall the primary purpose of Benedict's test, which is to detect reducing sugars.
Systematically evaluate each option to determine if it is a reducing sugar.
Option A, Acetone, is a ketone body.
Option B, Glucose, is a well-known reducing sugar.

Concept Tested & Keywords

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E6 Biochemistry U Satyanarayana— Part 2 (pp 421-820 of 840) p. 367-369

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

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 188-190

Practise the full RML 2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.