Heme metabolism Total<unk>  = direct<unk>  + indirect<unk>  Elevation of both alanine aminotransferase (ALT) and<unk>  is more indicative of serious liver injury than is elevation in ALT alone, as postulated in Hy's law that elucidates the relation between the lab test results and drug-induced liver injury Indirect (unconjugated) The measurement of unconjugated<unk>  (UCB) is underestimated by measurement of indirect<unk> , as unconjugated<unk>  (without/yet glucuronidation) reacts with diazosulfanilic acid to create azobilirubin which is measured as direct<unk> . Direct Direct<unk>  = Conjugated<unk>  + delta<unk>  Conjugated In the liver,<unk>  is conjugated with glucuronic acid by the enzyme glucuronyltransferase, first to<unk>  glucuronide and then to<unk>  diglucuronide, making it soluble in water: the conjugated version is the main form of<unk>  present in the "direct"<unk>  fraction. Much of it goes into the<unk> e and thus out into the small intestine. Though most<unk> e acid is reabsorbed in the terminal ileum to participate in enterohepatic circulation, conjugated<unk>  is not absorbed and instead passes into the colon. There, colonic bacteria deconjugate and metabolize the<unk>  into colorless urobilinogen, which can be oxidized to form urobilin and stercobilin. Urobilin is excreted by the kidneys to give urine its yellow color and stercobilin is excreted in the feces giving stool its characteristic<unk> own color. A trace (~1%) of the urobilinogen is reabsorbed into the enterohepatic circulation to be re-excreted in the<unk> e. Conjugated<unk> 's half-life is shorter than delta<unk> . Delta<unk>  Although the terms direct and indirect<unk>  are used equivalently with conjugated and unconjugated<unk> , this is not quantitatively correct, because the direct fraction includes both conjugated<unk>  and δ<unk> . Delta<unk>  is albumin-bound conjugated<unk> . In the other words, delta<unk>  is the kind of<unk>  covalently bound to albumin, which appears in the serum when hepatic excretion of conjugated<unk>  is impaired in patients with hepatobiliary disease. Furthermore, direct<unk>  tends to overestimate conjugated<unk>  levels due to unconjugated<unk>  that has reacted with diazosulfanilic acid, leading to increased azobilirubin levels (and increased direct<unk> . δ<unk>  = total<unk>  – (unconjugated<unk>  + conjugated<unk>  Half-life The half-life of delta<unk>  is equivalent to that of albumin since the former is bound to the latter, yields 2–3 weeks. A free-of-bound<unk>  has a half-life of 2 to 4 hours. Urine Under normal circumstances, only a very small amount, if any, of urobilinogen, is excreted in the urine. If the liver's function is impaired or when<unk> ary drainage is blocked, some of the conjugated<unk>  leaks out of the hepatocytes and appears in the urine, turning it dark amber. However, in disorders involving hemolytic anemia, an increased number of red blood cells are<unk> oken down, causing an increase in the amount of unconjugated<unk>  in the blood. Because the unconjugated<unk>  is not water-soluble, one will not see an increase in<unk>  in the urine. Because there is no problem with the liver or<unk> e systems, this excess unconjugated<unk>  will go through all of the normal processing mechanisms that occur (e.g., conjugation, excretion in<unk> e, metabolism to urobilinogen, reabsorption) and will show up as an increase of urobilinogen in the urine. This difference between increased urine<unk>  and increased urine urobilinogen helps to distinguish between various disorders in those systems.
Bilirubin
Lumirubin
Bile acid
Uric acid
Lipoprotein
Blood protein
Hemoglobin
Alanine transaminase