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Benedict’s test – Principle, Procedure and Results

Benedict’s test can be used as a Semiquantitative analysis of glucose in urine. Normal urine does not contain glucose. The commonest reducing substance found in urine is glucose, but other sugars occasionally found in urine also reduce Benedict’s reagent. Lactose may be present in the urine of pregnant and lactating women. Galactose and Fructose be present in inherited diseases. Besides these sugars, other substances which may occasionally find sufficient concentration in urine to reduce Benedict’s reagent include ascorbic acid, creatinine, urate, and drugs such as salicylates, penicillin, streptomycin, isoniazid etc.

Benedict’s test Principle

When alkaline copper (II) sulfate is heated in the presence of glucose or other reducing substances, it is reduced to cuprous (1) oxide and the amount of glucose present can be assessed by the formation of a greenish-yellow to red precipitate. NaOH is added to the reaction to produce heat which enhances the forward reaction.

Materials

  • Boiling test tubes
  • Graduated pipettes
  • Beakers
  • Benedict’s solution

Benedict’s test Procedure

  1. Urine sample is collected in to a clean ontainer.
  2. Take 5ml of Benedict’s solution in to a boiling tube.
  3. Add 8 drops of urine in to the tube.
  4. Mix and heat for 5 minutes
  5. Remove from the heat and allow it to cool slowly.
  6. Observe the color change and precipitate

The result should be recorded immediately because any colour change after the 15 seconds incubation leads to interpreting an erroneous result.

Observation and interpretation

Negative – Blue (Cler or cloudy)

Trace – Green with no precipitate

+ Green with precipitate

++ Yellow

+++ Orange

++++ Brick red

Chemical examination of urine – Read more

Fouchet’s test – Harrison spot test (bile pigments in urine) – Watch now

Ushan

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