Gerhardt’s test Principle, Procedure, Result.

Gerhardt’s test Definition

  • Gerhardt’s test is a type of laboratory test which is performed for the qualitative detection of ketone bodies in urine.
  • During the “ketosis” three ketones bodies or acetone bodies are found in the urine which are the products of fat metabolism, known as acetone (2%), acetoacetic acid (20%) and beta-hydroxybutyrate (78%).
  • During starvation and uncontrolled diabetes, the Ketone bodies are synthesized within the liver to re-utilized energy. These are types of acid that can results in metabolic acidosis in uncontrolled diabetes.
  • If the rate of ketone bodies production exceeds, the excess amounts of ketone bodies will be eliminated through the urine and the condition is termed as ketonuria. Acetone is volatile and also excreted in breath.
  • Ketosis may be correlated with diabetes mellitus termed Diabetic ketoacidosis, or it may be due to starvation, persistent vomiting and high fat and low carbohydrate diet.
  • There are present different methods for the detection of ketones in urine such as Rothera’s test, Gerhardt’s test, Lang’s test, Lindeman’s test, Han’s test, and Tablet test. All the tests used for the detection of ketonuria are based on the principle of Rothera’s nitroprusside test.
  • This method only can detect about 25 to 50 mg/dl of acetoacetic acid, that’s why it’s not considered a very sensitive test.


  • To detect the presence of ketone bodies within the supplied urine sample.

Gerhardt’s test Principle

In Gerhardt’s test, the ferric chloride reacts with the acetoacetic acid and forms a port wine or Bordeaux red color. This test only identifies acetoacetic acid, Acetone and beta-hydroxybutyrate can’t be detected by this method. It also detects salicylates in urine.

During this test, if the color disappears, it means the acetoacetic acid is present within the sample. On boiling acetoacetic acid loses carbon dioxide and transforms into acetone. Acetone doesn’t react with ferric chloride. If the color persists, acetoacetic acid is absent. The previous color is due to salicylates.

Requirements of Gerhardt’s test 

  • Specimen: Urine
  • Glassware: Test tubes
  • Chemical:10% Ferric chloride (10ml of ferric chloride in 100 ml of distilled water).

Gerhardt’s test Procedure

  1. Take a clean test tube and add about 3-5 ml of urine to it.
  2. Then add 5ml of ferric chloride to the test tube. If phosphates are present, they get precipitated as ferric phosphates.
  3. If the diacetic acid is present, a Bordeaux red color will develop in addition to ferric chloride.
  4. After that boil the test solution for 5 minutes to confirm the presence of acetoacetic acid within the supplied urine sample.
  5. Now observe the test tubes for color change.
Gerhardt's test
Gerhardt’s test

Observations and Results

  • Positive Test: If the color disappears, the Acetoacetic acid is present within the urine. 
  • Negative Test: If the color persists, acetoacetic acid is absent within the urine sample.


  • Wash the apparatus before and then after the experiment.
  • Carefully manage all the chemicals within the laboratory.
  • Don’t touch the urine sample during the experiment.
  • Holds the test tubes by using test tube holders.
  • Use a clear and clean test tube, make sure the test tubes are free of any dirt and chemicals because this will give a false result.
  • Place all the apparatus in their respective place after the completion of the experiment.