Follow the Pigment
In the diazo method, an accelerator is added to measure total bilirubin. Why is the accelerator needed?
To allow unconjugated bilirubin to react with the diazo reagent, so both conjugated and unconjugated fractions can be measured.
Increased RBC destruction causes increased indirect bilirubin, negative urine bilirubin, and increased urine urobilinogen. This is which pattern?
What is a prehepatic (hemolytic) pattern?
These two aminotransferases are used primarily as markers of hepatocellular injury rather than hepatic synthetic function.
What are AST and ALT?
AST/ALT are disproportionately elevated relative to their reference limits.
A patient has:
total bilirubin 6.0 mg/dL
direct bilirubin 0.5 mg/dL
negative urine bilirubin
increased urine urobilinogen.
What process is most likely?
What is increased RBC destruction (hemolysis)?
This enzyme adds glucuronic acid to bilirubin in hepatocytes, making it water-soluble.
What is UDP-glucuronosyltransferase (UGT1A1), the bilirubin conjugating enzyme?
AST and ALT are markedly elevated compared with ALP. This pattern primarily suggests injury to these cells.
What are hepatocytes?
ALP is elevated, but the source could be bone or liver. Which additional enzyme supports a hepatobiliary source when elevated?
What is GGT (gamma-glutamyl transferase)?
A patient with severe acute hepatic injury has a markedly prolonged PT/INR but normal albumin.
Which result more readily reflects the acute loss of hepatic synthetic function?
What is the prolonged PT/INR?
After intestinal bacteria convert bilirubin into urobilinogen and related intermediates, this pigment contributes to the brown color of stool.
What is stercobilin?
A patient has elevated direct bilirubin, positive urine bilirubin, dark urine, and markedly decreased urine urobilinogen. What is the most likely pattern?
What is cholestatic pattern, suggesting significant biliary obstruction?
A patient has:
AST 900 U/L
ALT 1,100 U/L
ALP 130 U/L
Which laboratory pattern predominates?
What is a hepatocellular injury pattern?
A patient has low albumin, prolonged PT/INR, and mildly elevated AST and ALT.
Which disease stage is more consistent with this combination when the clinical context supports chronic liver dysfunction?
What is advanced chronic liver disease?
Total bilirubin is 5.0 mg/dL and direct bilirubin is 0.8 mg/dL. Calculate the indirect bilirubin and identify the predominant bilirubin fraction.
What is 4.2 mg/dL?
Indirect = total − direct.
Indirect bilirubin: 4.2 mg/dL
Direct bilirubin: 0.8 mg/dL
The predominant fraction is unconjugated (indirect) bilirubin.
Which two inherited disorders are associated with predominantly conjugated hyperbilirubinemia due to impaired hepatic handling or excretion?
What are Dubin–Johnson syndrome and Rotor syndrome?
Why is an isolated elevation in AST less specific for liver injury than an elevation in ALT?
Because AST is also found in skeletal muscle, heart, and other tissues.
A patient has decreased albumin.
Name two nonhepatic conditions that can also cause this finding and complicate interpretation of liver synthetic function.
What are malnutrition and nephrotic syndrome?
Inflammation is another acceptable answer.
A patient has mild unconjugated hyperbilirubinemia, normal AST, ALT, ALP, and albumin, and negative urine bilirubin. Which inherited condition is most likely?
What is Gilbert syndrome?
A patient has elevated ALP, increased direct bilirubin, positive urine bilirubin, and low urine urobilinogen. Which category of liver disorder best explains the results?
What is a cholestatic/obstructive disorder?
A patient with advanced chronic liver disease has only mildly elevated AST and ALT but low albumin and prolonged PT/INR.
Why do the modest enzyme elevations not exclude severe disease?
What is that AST and ALT measure cellular injury, not remaining hepatic functional reserve?
A patient has:
total bilirubin 8.0 mg/dL
direct bilirubin 6.7 mg/dL
positive urine bilirubin
markedly decreased urine urobilinogen
ALP disproportionately higher than AST and ALT
Identify the most likely pattern and explain the urine findings.
What is cholestatic pattern consistent with biliary obstruction?
Conjugated bilirubin backs up into blood and can enter urine because it is water-soluble, while little bilirubin reaches the intestine to form urobilinogen.