quiz 2 review liver function Flashcards
List the specimens that could be collected and the metabolic analytes that could be measured in each to evaluate bilirubin metabolism/liver function
Serum/Plasma - to measure direct and indirect bilirubin
Urine - to measure urobilinogen and bilirubin
Feces - to measure urobilinogens, and urobilin/stercobilin
Why is the liver’s blood supply unique?
The liver has a dual circulation - hepatic and portal.
Hepatic artery - brings oxygenated blood to the liver
Hepatic veins - brings deoxygenated blood away from the liver
Portal vein - brings blood from the GI tract to the liver
Why is the liver called a metabolic factory. Give three examples.
The liver is involved in the metabolism of carbohydrates, proteins and lipids. See pages 62-63 in study guide
What is the purpose of an accelerator in Diazo methods for bilirubin? Name 2 accelerators
The accelerator allows indirect bilirubin to react with the diazo reagent.
Accelerators: methanol, caffeine sodium benzoate
Differentiate between the terms direct and indirect bilirubin
Indirect bilirubin (aka unconjugated bilirubin)
- is non polar and is not soluble in water. Indirect bilirubin binds to albumin to be transported to the liver.
- will only react with a diazo reagent in the presence of an accelerator (ex. alcohol, caffeine).
- does not appear in urine (isn’t filtered through the kidney)
Direct Bilirubin (AKA conjugated bilirubin)
- bilirubin that has been conjugated with glucuronate (glucuronic acid)
- polar and water soluble
- does appear in urine when blood levels are increased
What is azobilirubin?
Azobilirubin is an indicator formed from the reaction of bilirubin with diazo reagent
Why isn’t the Direct Spectrophotometric Method for bilirubin suitable for use with adult sera?
The direct spectrophotometric method can only measure total bilirubin and can only be used in infants up to three months of age.
Children (> 3 months old) and adults have carotene and other pigments in their serum that will also absorb at 454 nm which will falsely elevate results.
What is the purpose of alkaline tartrate in the Jendrassik-Grof method for bilirubin?
The alkaline tartrate changes the pH to 13 (alkaline) and converts red azobilirubin to a blue color which can be measured at 600 nm
Why should a hemolyzed specimen not be used for bilirubin measurement?
Hemoglobin competes for the diazo reagent and gives a falsely low result for bilirubin
What happens to bilirubin in a urine specimen left sitting at room temperature for 3 hours?
Bilirubin is unstable and disappears in 2 ways:
- hydrolyzed to free bilirubin
- oxidized to biliverdin
Exposure to light causes up to a 50% decrease per hour.
Is physiologic jaundice of the newborn always a clinically normal occurrence?
No, it would be considered abnormal in any of the following instances:
- if it appears during the first 24 hours after birth
- if it exceeds approximately 204 μmol/L in full term infants and approximately 342 μmol/L in premature infants
- if it remains elevated after the first week in full term infants
- if there is an increase in conjugated bilirubin above reference values
In a pre-hepatic jaundice, why is the urine bilirubin negative?
The urine bilirubin is negative in a pre-hepatic jaundice because it is unconjugated bilirubin that is elevated in the blood. Since unconjugated bilirubin is water insoluble it can’t be excreted by the kidneys.
What is intrahepatic cholestasis and when does it occur?
Intrahepatic cholestasis refers to stasis (no movement) of bile in the liver. This occurs with hepatocellular damage (intrahepatic jaundice) and long-term obstruction leading to liver cell damage.
A patient having clay-colored stools should be suspected of having which type of jaundice? Explain.
The brown stool color comes from the oxidation of urobilinogen to urobilin and the oxidation of stercobilinogen to stercobilin. A decrease in urobilin or stercobilin would cause the clay-colored stools. A patient with clay-colored stools would be suspected of having post-hepatic obstructive jaundice
Classify the following set of laboratory findings into one of the three major types of jaundice.
Total bilirubin 65 μmol/L Indirect bilirubin 20 μmol/L Direct bilirubin 45 μmol/L Urine urobilinogen Negative Fecal urobilinogen Negative
Post hepatic obstructive jaundice
Both total bilirubin and direct bilirubin are elevated. The direct (conjugated) bilirubin is not present in the urine or feces (both negative), suggesting that there is an obstruction preventing its excretion.
