3. Reducing sugar
Called “reducing” because it has a free ketone or
aldehyde group which can be donated
Examples of reducing sugar:
- Glucose
- fructose
4. Reason to test?
- Presence of detectable amount reducing sugar in urine -
called “glycosuria”
- Presence of detectable amount of glucose in urine -
called “glucosuria”
5. Causes of glucosuria:
- Type 2 Diabetes Mellitus
- Pregnancy : Gestational diabetes mellitus(GDM)
- Severe burns
- IV corticosteroids
- Severe sepsis
6. Test for reducing sugar
Benedict’s test:
- Test to detect reducing sugars in urine
- It is a qualitative test and also semi-quantitative test
- Benedict’s reagent contains:
- Copper sulphate
- Sodium carbonate
- Sodium citrate
7. Principle
● Urine is added to blue coloured copper sulphate
solution.
● Cupric ion is reduced by glucose to cuprous oxide and
a coloured precipitate is formed.
8. ● Take 5 ml of Benedict’s qualitative reagent in a test
tube.
● Add 8 drops (or 0.5 ml) of urine.
● Heat to boiling for 2 minutes
● Look for colour change
Procedure
9.
10. Interpretation
No change of blue colour = Negative
Greenish colour = Traces (< 0.5 g/dl)
Green/cloudy green ppt = + (0.5-1 g/dl)
Yellow ppt = ++ (1-1.5 g/dl)
Orange ppt = +++ (1.5-2 g/dl)
Brick red ppt = ++++ (> 2 g/dl)
11.
12. Report:
The given sample contains: reducing sugar
Principle Observation Interpretation
0.5 ml of urine boiled
in 5 ml of Benedict’s
reagent.
Blue colour copper
sulphate is reduced in
the presence of
reducing sugar,
leading to colour
change
Orange colour seen Reducing sugar
present
13. Viva questions
Q: What does Benedict’s test detect?
Q: What does Benedict’s reagent contain?
Q: What is the principle and procedure of Benedict’s
test?
Q: What are the advantages of Benedict’s test?
- Simple, can be performed quickly
- Cheap
- It is both qualitative and quantitative
14. Q: What are the limitations of Benedict’s test?
- False positive due to drugs like penicillin, isoniazid,
streptomycin, salicylate
- Exact concentration cannot be measured, only
rough estimate
