Icterus Flashcards
hyperbilirubinemia
elevated serum or plasma bilirubin
does NOT always cause icterus
normal bilirubin concentration
<0.2 mg/dL
at what concentration is bilirubin detectable in plasma (icteric plasma)
> 0.5 mg/dL
at what concentration is bilirubin detectable in tissues (icterus)
> 2.0 mg/dL
icterus
yellowing of plasma caused by hyperbilirubinemia
bilirubinuria
bilirubin in the urine
ALWAYS pathologic in cats
can be normal in dogs
cholestasis
decrease in bile flow
intrahepatic cholestasis
slow, congested liver causing impaired bile flow
extrahepatic cholestasis
biliary system obstruction
bile
water + bile acids + bile salts + bilirubin + cholesterol + FAs + lecithin + electrolytes + bicarbonate
continuously produced by the LIVER and released into duodenum OR stored and concentrated in the gallbladder
what are the functions of bile
- fat emulsification and digestion
- excretion of waste (bilirubin, cholesterol, drugs, toxins)
- bactericidal (maintains intestinal pH to prevent dysbiosis)
steps of bilirubin metabolism
physiologic extravascular hemolysis:
1. RBC breaks down into heme and globin
2. heme enters the spleen and gets taken up by splenic macrophages
3. heme –> biliverdin
4. biliverdin –> unconjugated bilirubin
5. UC bilirubin (lipid soluble) binds albumin to travel to liver
6. UC bilirubin –> C bilirubin in the liver
7. C bilirubin (water soluble) gets released into bile
8. bile –> intestines –> deconjugation by microbes to form urobilinogen + stercobilin
9. stercobilin released in feces; urobilinogen travels to kidneys OR enterohepatic circulation back to the liver
10. urobilinogen –> urobilin in kidneys –> released in urine
what are the three mechanisms of icterus
- prehepatic
- hepatic
- posthepatic
prehepatic icterus
hemolytic anemia
PATHOLOGIC extravascular hemolysis –> exceeds normal bilirubin levels –> hyperbilirubinemia
elevated UNCONJUGATED bilirubin
hepatic icterus
primary liver dysfunction caused by:
1. decreased functional liver mass
2. functional cholestasis (intrahepatic)
elevated UNCONJUGATED or CONJUGATED bilirubin
posthepatic icterus
biliary system dysfunction caused by:
1. extrahepatic bile duct obstruction (EHBDO)
2. gallbladder rupture
elevated CONJUGATED bilirubin
clinical signs associated with icteric patients
icterus - sclera, pinnae, MM
weight loss
inappetance
vomiting
diarrhea
+/- abdominal pain (EHBDO), hepatomegaly, effusion
differentials for prehepatic icterus
hemolytic anemia
1. IMHA
2. heinz body anemia (oxidative damage - zinc, onion, acetaminophen tox)
3. infectious (mycoplasma, babesia)
4. transfusion reaction
5. microangiopathic (DIC, splenic HSA, heartworm)
6. severe hypophosphatemia
differentials for hepatic icterus
liver disease
cats:
1. hepatic lipidosis
2. cholangitis
3. FIP
dogs:
1. chronic hepatitis - immune vs copper associated
2. cholangiohepatitis
3. cirrhosis
both:
1. neoplasia - lymphoma
2. acute or chronic toxins
3. bacteremia –> cholestasis of sepsis
differentials for posthepatic icterus
- obstruction
- pancreatitis
- GB mucocele
- cholecystitis
- neoplasia
- choledocolith
- CBD or major duodenal papilla stricture - GB or bile duct rupture
what lab values are consistent across all mechanisms of icterus
hyperbilirubinemia
icteric plasma
+/- bilirubinuria
prehepatic icterus lab values
CBC: regenerative anemia w/ normal protein
- morphology: spherocytes, heinz bodies, schistocytes
chem: reactive hepatopathy
hepatic icterus lab values
CBC: mild NNN anemia +/- leukogram changes
Chem:
- hypoalbuminemia
- HYPOCHOLESTEROLEMIA
- low BUN and glucose
liver enzymes will be more elevated in DOGS than cats due to longer half lives and greater total number of enzymes
UA: isosthenuria from medullary washout (low BUN)
posthepatic lab values
Chem:
- marked HYPERCHOLESTEROLEMIA
- +/- elevated liver enzymes
what is the most important diagnostic for differentiating hepatic from posthepatic icterus
ultrasound
- hepatomegaly –> acute liver disease vs neoplasia
- microhepatica –> chronic liver disease vs shunt
- GB/biliary distension –> EHBDO
r/o pancreatitis, mucocele, masses, choleliths, choledocoliths, strictures
what additional diagnostics are useful in icteric patients
- ammonia –> r/o hepatic encephalopathy
- coag panel –> r/o liver dysfunction
- liver FNA and biopsy –> r/o differentials for liver disease
- thoracic radiographs –> if suspected neoplasia
- CT scan –> EHBDO, PSS, surgical planning
bile acids are generally NOT indicated with hyperbilirubinemia
treating prehepatic icterus
treat underlying cause of hemolysis
treating hepatic icterus
treat underlying hepatopathy
treating posthepatic icterus
surgical:
- mature mucoceles
- severe cholecystitis
- GB rupture
- masses
- severe pancreatitis
medical:
- pancreatitis
- mild cholecystitis
- immature mucocele
