Approach to Icterus Flashcards
Describe bilirubin physiology
RBCs last about 7 weeks in circulation, once they are done with their job they are recycled and stripped for parts
-hemoglobin is particularly valuable
-macrophages or monocytes will break down hemoglobin into iron and biliverdin, and then further reduces biliverdin into unconjugated bilirubin
-the liver then conjugates bilirubin to form soluble bilirubin (soluble in water/bile)
-soluble bilirubin can now be excreted into the duodenum in bile
T/F: If there is a lot of unconjugated bilirubin in the bloodstream, that means the liver is the problem
False- this is possible but it is not necessarily true in every case
T/F: the bilirubin in the bile is always conjugated
True- it only can enter the bile after it is conjugated and becomes soluble
Why should you pay attention to even very mild increases in bilirubin?
The liver is really good at its job at excreting bilirubin, so the reference range is very narrow
What is the difference between pre-hepatic, hepatic and post hepatic hyperbilirubinemia?
-Pre-hepatic=more RBCs are being broken down than normal (hemolysis) which overwhelms the normal elimination system
-Hepatic=liver is not doing job of conjugating the bilirubin, so it is not being secreted into bile and eliminated. Normal amount of RBCs are being destroyed
-Post hepatic= normal RBC # being broken down, normal conjugation occurring in liver, but there is something downstream of the liver preventing it from exiting the body (obstruction between liver and duodenal papillae)
What are the different causes of pre-hepatic hyperbilirubinemia?
Immune mediated destruction of RBCs
Toxic destruction (ex: zinc)
Post transfusion- commonly see mild destruction due to older RBCs/storage lesions or some trauma during injection
What clinical exam finding would put pre-hepatic hyperbilirubinemia high on your list?
Anemia
What are some of the causes of hepatic hyperbilirubinemia?
Liver failure (functional problem)- not just liver injury
-toxicity (sagal palm)
-infectious hepatitis (we vaccinate against most of the viral infection)
-cirrhosis- scarring of liver
-portosystemic shunts (early cases wont be icteric, occurs in end stage)
-microvascular dysplasia: vasculature of liver not working, bypassing functional units of liver
-secondary injury (such as hepatic lipidosis)
-congenital deficiencies (such as copper storage disease)
*liver failure not seen as much as other causes, but once hepatic cause is identified for hyperbilirubinemia, prognosis is poor
What are some causes of post hepatic hyperbilirubinemia?
-gall bladder mucocele
-cholelithiasis
-pancreatitis*
-tumors- within biliary system, within intestines
Pancreatitis and gall bladder mucocele most common in dogs, pancreatitis and tumors most common in cats
When you see yellow gums, what should you think? What about orange gums?
Yellow-prehepatic causes
Orange- hepatic or post hepatic causes
How can you differentiate between post hepatic and hepatic icterus?
Physical exam findings wont help much
- need bloodwork (liver enzyme elevations)
What are the liver leakage enzymes? What are the inducible (cholestatic) enzymes? What are the pseudofunction analytes? What are the analytes specific to liver?
Leakage: ALT and AST
Cholestatic: ALP and GGT
-can also increase with steroid use
Pseudofunction: BUN, Glucose, Cholesterol, Albumin
- occurs with very severe liver damage (end stage)
- and they can be impacted by many other things
Liver specific: bile acids and ammonia
What are the diagnostics that will help the most in diagnosing a cause of hepatic hyperbilirubinemia? Post-hepatic?
Hepatic- bloodwork
Post hepatic- imaging
- look for reason for obstruction (distended gall bladder?, distension of common bile duct is most specific)
- hardest one is pancreatitis: imaging is not very sensitive, neither is anything else
- belly pain
What diagnostics should always be run on an icteric patient?
PCV/TS or CBC
-blood smear
-chemistry
-ammonia (if worried about hepatic causes)
-don’t run bile acids routinely as elevated bilirubin
will interfere with results
-abdominal radiographs
-abdominal ultrasound
-others depending on above
How much hyperbilirubinemia is needed to see icterus clinically?
3 mg/dL
