Detection of Bile Pigments in Urine for Laboratory Investigation

Introduction

Bile pigments are breakdown products of hemoglobin metabolism, primarily bilirubin and biliverdin. Under normal conditions, bile pigments are not present in urine. Their presence indicates hepatic or post-hepatic disorders, especially conditions associated with obstructive jaundice. Detection of bile pigments in urine is an important qualitative test in routine clinical laboratory diagnosis.

Principle

Bile pigments in urine are detected by their ability to undergo oxidation in the presence of strong acids and oxidizing agents. When urine containing bilirubin is treated with concentrated nitric acid, it gets oxidized to biliverdin and other intermediate pigments, producing a characteristic play of colors (green, blue, violet, red, and yellow).
This reaction forms the basis of Fouchet’s test or Gmelin’s test used for detecting bile pigments in urine.

Specimen

• Fresh urine sample

• Preferably early morning midstream urine

  
  

Reagents

For Gmelin’s Test

• Concentrated nitric acid (containing nitrous acid)

For Fouchet’s Test

• Fouchet’s reagent

  • Trichloroacetic acid

  • Ferric chloride

  • Distilled water

Equipment

• Test tubes

• Dropper

• Filter paper

• Glass rod

  
  

Procedure

A. Gmelin’s Test

1. Take 2–3 mL of urine in a clean test tube.

2. Carefully add 1 mL of concentrated nitric acid along the side of the test tube without mixing.

3. Observe the junction of the two liquids.

Observation

• Formation of a ring with multiple colors (green, blue, violet, red, yellow) indicates a positive test.

Interpretation

• Positive: Presence of bile pigments

• Negative: No color ring formed

B. Fouchet’s Test

1. Take 5 mL of urine and add 2 mL of Fouchet’s reagent.

2. Mix and allow it to stand for a few minutes.

3. Filter the mixture through filter paper.

4. Observe the color on the filter paper.

Observation

• Green or blue-green coloration on the filter paper indicates bile pigments.

Normal Result

• Bile pigments: Absent in urine

Clinical Significance

Presence of bile pigments in urine is seen in:

• Obstructive jaundice

• Hepatitis

• Cirrhosis of liver

• Cholestasis

Urine bile pigments help differentiate hepatic and obstructive jaundice from hemolytic jaundice, where bile pigments are usually absent.

Advantages

• Simple and rapid qualitative tests

• Useful in routine screening

• Requires minimal equipment

Limitations

• Not quantitative

• False negatives may occur in old urine samples

• Sensitive to light and oxidation

Precautions

• Use fresh urine samples

• Handle concentrated nitric acid carefully

• Avoid contamination

• Perform the test away from direct sunlight

Conclusion

Detection of bile pigments in urine is a valuable laboratory investigation in the evaluation of liver and biliary tract disorders. Gmelin’s and Fouchet’s tests provide quick and reliable qualitative assessment and are commonly employed in routine clinical laboratories.