vandenbergh reaction, it's principle and interpretation use harpers and lippincott as your source
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The Van den Bergh Reaction
Background
The van den Bergh reaction (also written "van den Berg" or "Vandenbergh reaction") was originally described by A.A.H. van den Bergh and P. Muller in 1916. It remains the foundation for bilirubin measurement in clinical chemistry laboratories worldwide.
Principle
The reaction is based on the colorimetric diazo reaction. The reagent used is diazotized sulfanilic acid (a diazo reagent). When bilirubin reacts with this reagent, it is cleaved at the central methane bridge, producing two red azodipyrole (azopigment) molecules, which are measured colorimetrically.
"Bilirubin is commonly measured by the van den Bergh reaction, in which diazotized sulfanilic acid reacts with bilirubin to form red azodipyroles that are measured colorimetrically."
- Lippincott Illustrated Reviews: Biochemistry, 8th ed., p. 805
"Quantitation of bilirubin employs a colorimetric method based on the reddish-purple color formed when bilirubin reacts with diazotized sulfanilic acid."
- Harper's Illustrated Biochemistry, 32nd ed., p. 334
The reaction is performed in two phases:
Phase 1 - Direct Reaction (without methanol)
- Performed in aqueous solution only, no methanol added
- Conjugated bilirubin (CB) - being water-soluble - reacts rapidly with the diazo reagent, within 1 minute
- This is called the "direct-reacting" fraction
- Corresponds to bilirubin glucuronide (mono- and diglucuronides)
Phase 2 - Total Bilirubin (with methanol)
- Methanol is added to the reaction mixture
- Methanol dissolves the unconjugated bilirubin (UCB), which is otherwise too insoluble in aqueous solution to react well
- Now both CB and UCB react with the reagent
- This gives the total bilirubin value
Calculation - Indirect Fraction
Indirect bilirubin = Total bilirubin - Direct bilirubin
The indirect-reacting bilirubin corresponds to unconjugated bilirubin (UCB).
"An assay conducted in the absence of added methanol measures 'direct bilirubin,' which is bilirubin glucuronide. An assay conducted in the presence of added methanol measures total bilirubin. The difference between total bilirubin and direct bilirubin is known as 'indirect bilirubin,' and is unconjugated bilirubin."
- Harper's Illustrated Biochemistry, 32nd ed., p. 334-335
Interpretation
Normal Values
- In normal plasma, only ~4% of total bilirubin is conjugated (direct-reacting), because most CB is secreted efficiently into bile. (Lippincott, 8th ed., p. 805)
- Hyperbilirubinemia is defined as serum bilirubin > 1 mg/dL (17 μmol/L)
- Clinical jaundice (icterus) becomes visible when bilirubin reaches 2 to 2.5 mg/dL, as it diffuses into tissues. (Harper's, 32nd ed., p. 335)
What the Fractions Mean Clinically
| Fraction | Corresponds To | Significance |
|---|---|---|
| Direct bilirubin (elevated) | Conjugated bilirubin | Obstructive/hepatocellular jaundice; conjugated bilirubin can appear in urine (choluria) |
| Indirect bilirubin (elevated) | Unconjugated bilirubin | Hemolytic jaundice, neonatal jaundice, Crigler-Najjar, Gilbert syndrome |
Types of Hyperbilirubinemia - Interpretation
Elevated indirect (unconjugated) bilirubin - causes include:
- Hemolytic anemias (overproduction exceeds liver conjugation capacity)
- Neonatal "physiologic jaundice" (immature UGT enzyme activity)
- Crigler-Najjar syndrome Types I and II (absent or reduced UDP-glucuronosyltransferase)
- Gilbert syndrome (~30% UGT activity retained; benign)
- Toxic hyperbilirubinemia (liver parenchymal damage impairing conjugation)
UCB is lipid-soluble and crosses the blood-brain barrier, causing kernicterus when albumin binding capacity (~20-25 mg/dL) is exceeded.
Elevated direct (conjugated) bilirubin - causes include:
- Biliary tree obstruction (stone in common bile duct, pancreatic head cancer) - most common cause
- Liver diseases (hepatitis, cirrhosis with intrahepatic cholestasis)
- Dubin-Johnson syndrome
- Rotor syndrome
CB is water-soluble, appears in urine (choluria), and does not cross the blood-brain barrier.
(Harper's Illustrated Biochemistry, 32nd ed., Table 31-3, p. 335; Lippincott Illustrated Reviews: Biochemistry, 8th ed., p. 802-805)
Summary Table
| Parameter | Direct (Van den Bergh) | Indirect |
|---|---|---|
| Reagent condition | Aqueous solution only | After methanol addition (total - direct) |
| Reacts with | Conjugated bilirubin | Unconjugated bilirubin |
| Speed of reaction | Fast (<1 min) | Slow without alcohol |
| Water solubility | Water-soluble | Lipid-soluble |
| Appears in urine | Yes (choluria) | No (acholuric jaundice) |
| Crosses blood-brain barrier | No | Yes (kernicterus risk) |
| Clinical elevation suggests | Obstructive/hepatocellular disease | Hemolysis, conjugation defects |
Sources:
- Harper's Illustrated Biochemistry, 32nd Ed. - "Measurement of Bilirubin in Serum," p. 334-335
- Lippincott Illustrated Reviews: Biochemistry, 8th Ed. - "E. Jaundice," p. 805
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