Basic Concepts in Clinical Biochemistry-A Practical Guide.7z

CuSO 4

Blue

þ2H 2 O!

sugar

Cu OHðÞ 2

white

þH 2 SO 4

2Cu OHðÞ 2 heat! Cu 2 O

Cuprous oxide

ðÞredor yellow

þ2H 2 OþO

11.2.2 Benedict’s Qualitative Reagent

Sol A: Dissolve 17.3 g of sodium citrate and 10 g of Na 2 CO 3 in about 60 ml of
distilled water with the aid of heat.
Sol B: Dissolve 1.73 g of CuSO 4 in 10 ml of distilled water.

Solution B is added to solution A gently with constant mixing, andfinal volume is
made up to 100 ml with distilled water.

12.6 Procedure

Take 5 ml Benedict’s reagent in a test tube and add 0.5 ml or eight drops of urine.
Mix and heat it to boil for 3–5 min and allow cooling. Observe the color, and report
the result on the basis of color produced as given in table below.

S. no Approximate amount of sugar Appearance of color change Result

1 Nil Blue Nil

2 Traces Bluish green +

3 0.5 g/dl Green precipitate +

4 1 g/dl Yellow precipitate ++

5 1.5 g/dl Brown precipitate +++

6 >2 g/dl Brick red precipitate ++++

Sensitivity of the test is 0.1–1.5% toward false-positive results obtained from
other reducing substances such as lactose, galactose, fructose, xylose, etc. Specific
tests are performed to rule out the possibility of presence of these sugars. Normal
constituents such as uric acid, creatinine, and ascorbic acid in higher amount also
give false-positive result.

11.3 CLINISTIX/Uristix................................

CLINISTIX are commercially available strips. These are impregnated with glucose
oxidase (GOD), peroxidase (POD), and dye O-toluidine (chromogen). In this reac-
tion, glucose is oxidized to gluconic acid and H 2 O 2 by the enzyme GOD. H 2 O 2
formed is split into water and nascent oxygen by POD enzyme. This nascent oxygen

50 11 To Perform Qualitative Test for Reducing Substances in Urine