Step 1: what comes next?
Confirm and fractionate bilirubin
Separate predominantly unconjugated from conjugated or mixed hyperbilirubinemia.
GI
Jaundice Differential
Fractionate first, then decide whether bilirubin was overproduced, mishandled, or obstructed.
- Use direct and indirect bilirubin to organize a jaundice differential.
- Interpret urine bilirubin and urobilinogen in physiologic context.
- Choose first diagnostic moves for hemolytic, hepatocellular, and cholestatic patterns.
Bilirubin route
Follow the pigment without skipping a compartment
The route distinguishes production, transport, conjugation, excretion, and downstream clues.
Quick check
A 42-year-old has jaundice, dark urine, pale stools, pruritus, and alkaline phosphatase elevation out of proportion to aminotransferases.
Which framework category is most likely?
Reason it through
- What makes urine dark?Water-soluble conjugated bilirubin is being excreted.
- What makes stool pale?Too little bilirubin pigment reaches the intestine.
- Which enzyme pattern supports the route?Disproportionate alkaline phosphatase elevation.
Three routes to yellow
The first useful split is mechanism, not a memorized list of diseases.
Prehepatic disease overproduces bilirubin, hepatocellular disease impairs uptake, conjugation, or excretion, and cholestasis blocks bile flow.
Mixed injury can raise both aminotransferases and alkaline phosphatase, so bilirubin fractionation, enzyme proportions, medication history, and imaging must be integrated.
Compare the mechanistic compartments.
Hemolysis or ineffective erythropoiesis produces predominantly unconjugated hyperbilirubinemia.
Hepatocyte injury can produce a mixed fraction with aminotransferase predominance.
Impaired canalicular or ductal flow produces conjugated hyperbilirubinemia with alkaline phosphatase predominance.
Before the liver, in the liver, or after bile leaves the hepatocyte.
Make the first diagnostic moves
A small initial dataset usually identifies the correct branch.
Start with total and direct bilirubin, AST, ALT, alkaline phosphatase, albumin, and prothrombin time or INR while checking medication, alcohol, travel, pain, fever, weight loss, and hemolysis clues.
Order a blood count, reticulocyte count, LDH, haptoglobin, and smear for suspected hemolysis; use right-upper-quadrant ultrasound first when cholestasis or obstruction is suspected.
Order the initial approach.
Step 2: what comes next?
Classify the enzyme pattern
Compare aminotransferase and alkaline phosphatase predominance and assess synthetic function.
Step 3: what comes next?
Interrogate context
Review drugs, toxins, infection risks, pain, fever, weight loss, anemia, and prior episodes.
Step 4: what comes next?
Test the leading compartment
Use hemolysis labs for indirect disease or ultrasound for cholestatic disease.
Step 5: what comes next?
Escalate targeted testing
Add serologies, autoimmune studies, cross-sectional imaging, MRCP, ERCP, or biopsy only as the branch requires.
Use enzyme dominance to orient the differential
Magnitude and proportion guide the branch, while bilirubin and synthetic markers grade consequence.
Aminotransferase predominance supports hepatocellular injury, whereas disproportionate alkaline phosphatase elevation supports cholestasis.
Rising INR, hypoglycemia, encephalopathy, sepsis, or obstruction with systemic illness increases urgency independent of the bilirubin number.
Rank the scenarios by need for urgent escalation.
Urine reveals bilirubin solubility
The dipstick sees conjugated bilirubin because albumin-bound unconjugated bilirubin is not filtered.
Urine bilirubin indicates conjugated hyperbilirubinemia and can appear with hepatocellular excretory failure or cholestasis.
Urine urobilinogen may rise when bilirubin delivery and enterohepatic cycling increase, as in hemolysis, and may fall when complete obstruction prevents bilirubin from reaching the gut.
Select the pattern most consistent with brisk hemolysis.
Trace bilirubin from spleen to stool
Every lab clue corresponds to a location on the route.
Heme breakdown produces unconjugated bilirubin, albumin carries it to liver, UGT-mediated conjugation makes it water soluble, and canalicular secretion sends it into bile.
Intestinal bacteria convert bilirubin to urobilinogen; derivatives are reabsorbed, excreted in urine, or oxidized into stool pigments.
Place each failure on the map.
Excess heme breakdown increases unconjugated bilirubin production.
UGT impairment in Gilbert or Crigler-Najjar syndromes raises unconjugated bilirubin.
Cholestasis causes reflux of conjugated bilirubin into blood and urine.
Reduced pigment delivery can produce pale stool and low urobilinogen.
Pattern plus context narrows the branch
Reveal one additional clue at a time instead of ordering every test at once.
Fever, right-upper-quadrant pain, and jaundice raise concern for acute cholangitis and require urgent antibiotics and biliary drainage assessment.
Severe hepatocellular injury with coagulopathy or encephalopathy demands urgent acute liver failure evaluation rather than outpatient etiologic sorting.
Reveal the clue that changes the next move.
Order hemolysis studies and inspect the smear.Consider Gilbert syndrome after excluding hemolysis and liver injury.Evaluate acute hepatocellular injury, toxins, ischemia, and viral causes.Begin with right-upper-quadrant ultrasound.Give antibiotics and arrange urgent biliary decompression.
Key laboratory clue
Choose the compartment that explains the pattern
Localize the defect in bilirubin handling before naming a syndrome.
Which framework category is most likely?
- Key finding. A 42-year-old has jaundice, dark urine, pale stools, pruritus, and alkaline phosphatase elevation out of proportion to aminotransferases.
- Answer. Cholestatic or obstructive jaundice
- Why. Conjugated bilirubin reaches urine while reduced bile delivery causes pale stool and pruritus.
- Board rule. Dark urine plus pale stool points downstream toward cholestasis.
Stage 1 of 3: Overview
Overview
Jaundice Differential
A small initial dataset usually identifies the correct branch.
Interpret the bilirubin patterns
Five presentations make fractionation and physiology do the sorting.
Cross out the wrong compartment and highlight the clue that localizes bilirubin handling. Each case follows the route step by step.
A 24-year-old develops mild scleral icterus during an overnight fast. Total bilirubin is 3.1 mg/dL, direct bilirubin is 0.3 mg/dL, and blood count, reticulocytes, AST, ALT, and alkaline phosphatase are normal.
Which diagnosis is most likely?
Reason it through
- Which bilirubin fraction dominates?The unconjugated fraction.
- Is there evidence of red-cell destruction?No.
- What trigger is classic for reduced conjugation reserve?Fasting.
Which bilirubin fraction dominates?Is there evidence of red-cell destruction?
- Which bilirubin fraction dominates?The unconjugated fraction.
- Is there evidence of red-cell destruction?No.
- What trigger is classic for reduced conjugation reserve?Fasting.
A 31-year-old has fatigue, jaundice, hemoglobin of 8.2 g/dL, reticulocytosis, elevated LDH, low haptoglobin, and no urine bilirubin.
Which compartment best explains the jaundice?
Reason it through
- What is the marrow doing?Increasing reticulocyte production.
- What do high LDH and low haptoglobin signal?Hemolysis.
- Why is urine bilirubin absent?The excess bilirubin is unconjugated and albumin bound.
What is the marrow doing?What do high LDH and low haptoglobin signal?
- What is the marrow doing?Increasing reticulocyte production.
- What do high LDH and low haptoglobin signal?Hemolysis.
- Why is urine bilirubin absent?The excess bilirubin is unconjugated and albumin bound.
A 68-year-old has painless jaundice, dark urine, pale stools, weight loss, and a markedly cholestatic enzyme pattern.
What is the best first imaging study?
Reason it through
- Which fraction likely enters urine?Conjugated bilirubin.
- What do pale stools imply?Reduced bile pigment reaching the intestine.
- What first test checks for duct dilation?Right-upper-quadrant ultrasound.
Which fraction likely enters urine?What do pale stools imply?
- Which fraction likely enters urine?Conjugated bilirubin.
- What do pale stools imply?Reduced bile pigment reaching the intestine.
- What first test checks for duct dilation?Right-upper-quadrant ultrasound.
A 45-year-old develops jaundice after a new medication. ALT and AST are markedly elevated, alkaline phosphatase is only mildly elevated, and bilirubin is mixed.
Which injury pattern is most likely?
Reason it through
- Which enzymes dominate?The aminotransferases.
- What exposure anchors causality?A new medication.
- What severity markers must be checked?INR, mental status, glucose, and trajectory.
Which enzymes dominate?What exposure anchors causality?
- Which enzymes dominate?The aminotransferases.
- What exposure anchors causality?A new medication.
- What severity markers must be checked?INR, mental status, glucose, and trajectory.
A 57-year-old has fever, right-upper-quadrant pain, jaundice, hypotension, and ultrasound evidence of a dilated common bile duct.
What management is most appropriate?
Reason it through
- What syndrome does the triad suggest?Ascending cholangitis.
- What do hypotension and dilation add?Severe infection plus an obstructed source.
- What two treatment arms are required?Antibiotics and urgent drainage.
What syndrome does the triad suggest?What do hypotension and dilation add?
- What syndrome does the triad suggest?Ascending cholangitis.
- What do hypotension and dilation add?Severe infection plus an obstructed source.
- What two treatment arms are required?Antibiotics and urgent drainage.
Rapid review
Three questions to check
Which framework category is most likely?
Cholestatic or obstructive jaundice. Conjugated bilirubin reaches urine while reduced bile delivery causes pale stool and pruritus.
Which bilirubin fraction dominates?
The unconjugated fraction.
Is there evidence of red-cell destruction?
No.
Medically reviewed
Fatima Ali, DO
PGY-1 Resident Physician in Psychiatry
University Hospitals, Columbia
DO from Kansas City University
Resident physician and founding medical reviewer at Bone Wizardry, focused on clinical accuracy, clear diagnostic reasoning, and practical board-oriented teaching across the curriculum.
Languages: English, Urdu
Primary reviewerFull physician profile
Medically reviewed
Sources
Bone Wizardry is a study resource for medical students. It is not medical advice.