Bilirubin

1
Bilirubin

• Slides pilfered from
• Bilirubin Physiology Dr. Lidofsky March 10,
  2006

2
Bilirubin is Derived from Heme
3
Bilirubin is a Hydrophobic CompoundAnd
potentially neurotoxic
Bilirubin deposition
Kernicterus
4
?Bilirubin Production
Hyperbilirubinemia
?Bilirubin Elimination
5
Solution to the ProblemConvert bilirubin to a
hydrophilic compound
Unconjugated(hydrophobic)
Conjugation
Conjugated(hydrophilic)
6
Overview of Bilirubin Metabolism
Productionfrom Heme
Br
Binding toAlbumin
Alb-Br
Plasma
Urine
BrG
Br
SinusoidalUptake
SinusoidalExport (minor)
Conjugation
BrG
CanalicularExport
Hepatocytes
BrG
Br bilirubin BrG conjugated bilirubin Alb
albumin
Bile
7
Clinical Chemistry of Bilirubin

• Normal concentration lt 1 mg/dl(95 unconjugated)
• Jaundice evident when gt 3 mg/dl
• Detection methodscolorimetric assays(estimate
  of fractions) reflectance spectroscopy(more
  accurate)HPLC(most accurate, not widely
  available)

8
Classical Measurement of BilirubinThe van den
Bergh reaction
Bilirubin diazosulfanilic acid
Azobilirubin (absorbs at 540 nm)
(so-called Direct Bilirubin)
Conjugated bilirubin reacts promptly.Unconjugated
bilirubin reacts more slowly.
EtOH makes all the bilirubin react
promptly. (Total Bilirubin)
Indirect Bilirubin Total Bilirubin - Direct
Bilirubin
9
Important Point
Direct bilirubin is not the same as conjugated
bilirubin. Indirect bilirubin is not the same as
unconjugated bilirubin.
10
Alternative Methods for Measurements of Bilirubin
FractionsReflectance spectroscopy
Serum immobilized on coated two thin
films Conjugated bilirubin absorbs at 400
nm.Unconjugated bilirubin absorbs at 460
nm. Note a fraction of conjugated
bilirubincovalently bound to albumin is not
detected onone of the films delta
bilirubin. This is not of clinical importance
11
Bilirubin Production

• 4 mg/kg daily(0.5 mol in 70 kg man)
• 70-80 from hemoglobinsenescent erythrocytes
• 20-30 from other hemoproteinshepatocyte turnover

12
Clinical CorrelateHeme overproduction leads to
unconjugated hyperbilirubunemia

• Hemoglobinhemolysismultiple transfusionsineffec
  tive erythropoeisis
• Myoglobinmajor trauma