Alternative: Benedict test
A color change occurs as cupric ion (Cu2+) in copper sulfate is reduced to cuprous (Cu1+) oxide. Cupric ions impart a blue color, while cuprous ions impart an orange-red.
Testing is performed on an aqueous suspension of stool (1 part stool to 2 parts deionized water). A Clinitest tablet is placed in a test tube containing 15 drops of the suspension liquid, which causes a reaction to occur. The color is read 15 seconds after the reaction stops.
|
Color Reading
|
Amount of Sugar
|
|
negative (blue)
|
NA
|
|
trace
|
0.25 g/dL
|
|
1+
|
0.5 g/dL
|
|
2+
|
0.75 g/dL
|
|
3+
|
1.0 g/dL
|
|
4+ (orange red)
|
>= 2.0 g/dL
|
Clinitest does not distinguish the type of sugar that is present, which may be glucose, lactose, fructose, galactose, sucrose, or pentoses. Thin-layer chromatography can be used to identify which sugar(s) is (are) present.
False negative results may occur:
(1) very high levels of reducing substances (may cause a rapid color change that can be missed if the tube is not observed continuously)
(2) hydrogen peroxide
(3) deterioration of the specimen (bacterial overgrowth consumes the sugars)
False positive results may occur:
(1) drugs (high amount ascorbic acid, cephalosporins, nalidixic acid, probenecid)
(2) creatine
Diatrizoates in X-ray dyes may obscure the color change.
