30.2.4 Result
Appearance of a purple/red ring at the junction of the two layers within 30–60 s
indicates the presence of acetone and diacetic acid. Based on the intensity of the
color formed, the result can be represented as grade from trace to 3+.
The presence ofL-dopa and phenyl pyruvic acid in urine may produce weak false
positive reactions. In case of suspicion of a false positive test, the urine sample is
heated in a test tube for 1 min, allowed to cool, and Rothera’s test is repeated. The
heated urine will not produce a positive Rothera’s test due to ketone bodies.
30.3 Gerhardt’s FeCl 3 Test for Acetoacetic Acid
This test is based on the reaction of FeCl 3 with acetoacetate producing a red wine
color. The test is non-specific, and antipyrine gives similar color.
30.3.1 Reagent
10% aqueous solution of FeCl 3.
30.3.2 Procedure
Take 5 ml of urine and add 10% FeCl 3 solution drop by drop. Red wine color
(purple) indicates positive test.
30.4 Ketostix Test for Acetone and Acetoacetate
Ketostix are plastic strips, one end of which is impregnated with sodium
nitroprusside and glycine. When these strips are immersed in urine, sodium
nitroprusside and glycine react with acetone and acetoacetate to give lavender or
purple color.
30.4.1 Procedure
Dip the test end of strip in fresh specimen of urine, and remove immediately, briefly
touching the tip on side of container to remove excess liquid. Compare color with
chart. Ketostix is sensitive to 10 mg/dl acetoacetic acid and 25 mg/dl acetone.
30.4 Ketostix Test for Acetone and Acetoacetate 121