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PORPHYRINS & BILE PIGMENTS / 285as prehepatic (eg, hemolytic anemias), hepatic (eg,hepatitis), and posthepatic (eg, obstruction of thecommon bile duct). Measurements of plasma totaland nonconjugated bilirubin, of urinary urobilinogenand bilirubin, and of certain serum enzymes aswell as inspection of stool samples help distinguishbetween these causes.REFERENCESAnderson KE et al: Disorders of heme biosynthesis: X-linked sideroblasticanemia and the porphyrias. In: The Metabolic andMolecular Bases of Inherited Disease, 8th ed. Scriver CR et al(editors). McGraw-Hill, 2001.Berk PD, Wolkoff AW: Bilirubin metabolism and the hyperbilirubinemias.In: Harrison’s Principles of Internal Medicine, 15thed. Braunwald E et al (editors). McGraw-Hill, 2001.Chowdhury JR et al: Hereditary jaundice and disorders of bilirubinmetabolism. In: The Metabolic and Molecular Bases of InheritedDisease, 8th ed. Scriver CR et al (editors). McGraw-Hill,2001.Desnick RJ: The porphyrias. In: Harrison’s Principles of InternalMedicine, 15th ed. Braunwald E et al (editors). McGraw-Hill,2001.Elder GH: Haem synthesis and the porphyrias. In: Scientific Foundationsof Biochemistry in Clinical Practice, 2nd ed. WilliamsDL, Marks V (editors). Butterworth-Heinemann, 1994.