In a patient with right‑lower‑quadrant pain, fever, leukocytosis and mildly elevated serum bilirubin (<2 mg/dL), how does the bilirubin level affect the diagnosis and management of suspected acute appendicitis?

Elevated Bilirubin in Suspected Appendicitis

Mildly elevated serum bilirubin (<2 mg/dL) in a patient with right-lower-quadrant pain, fever, and leukocytosis should NOT alter your diagnostic approach or delay imaging—proceed directly to CT abdomen/pelvis with IV contrast as you would for any patient with intermediate-to-high clinical suspicion of appendicitis. 1

Diagnostic Significance of Hyperbilirubinemia

Hyperbilirubinemia has poor diagnostic accuracy and should not be used to confirm or exclude appendicitis:

• Elevated bilirubin (>1.1 mg/dL) occurs in 36% of patients with any appendicitis versus 14% without appendiceal inflammation, but the positive likelihood ratio is only 2.62 and negative likelihood ratio is 0.75—both too weak to meaningfully change clinical decision-making 2

• Even when comparing perforated versus non-perforated appendicitis, hyperbilirubinemia shows a positive likelihood ratio of only 1.74 and negative likelihood ratio of 0.72, indicating minimal discriminatory power 2

• While bilirubin levels are statistically higher in appendicitis patients, they typically remain within the normal range (median 12.0 µmol/L in appendicitis vs. 8.0 µmol/L in normal appendix), making the finding clinically unreliable 3

Why Bilirubin Elevation Occurs

The mechanism involves bacterial translocation and endotoxin absorption from inflamed appendiceal tissue causing mild hepatic dysfunction, but this pathophysiologic explanation does not translate into useful diagnostic performance 4, 5

Current Guideline-Based Approach

The 2020 WSES Jerusalem Guidelines make no recommendation regarding bilirubin as a diagnostic biomarker for appendicitis:

• Biochemical markers (including bilirubin) represent a "promising" tool but require further high-quality evidence before clinical adoption 1

• The guidelines emphasize that diagnosis should never be based on laboratory values alone, particularly in elderly patients where atypical presentations are common 1

• Recommended biomarkers for routine use are WBC with differential, absolute neutrophil count, and CRP—not bilirubin 1

Practical Management Algorithm

For your patient with RLQ pain, fever, leukocytosis, and mildly elevated bilirubin:

1. Calculate a clinical risk score (AIR or Adult Appendicitis Score) combining symptoms, physical examination findings, WBC, and CRP 6, 7

2. Obtain CT abdomen/pelvis with IV contrast immediately for intermediate-to-high clinical suspicion (which your patient clearly has based on fever + leukocytosis + RLQ pain) 6, 7

   • Sensitivity: 96-100%, Specificity: 93-95% 6, 7
   • IV contrast is essential; oral contrast is unnecessary and delays diagnosis 6, 7

3. Ignore the bilirubin value in your diagnostic algorithm—it adds no meaningful information beyond what WBC and CRP already provide 2, 8

4. If CT confirms appendicitis, initiate broad-spectrum antibiotics immediately and proceed to appendectomy 7

What About Predicting Perforation?

Bilirubin is also unreliable for predicting complicated appendicitis:

• Although hyperbilirubinemia shows 93% specificity for perforation, the sensitivity is only 9.4%, meaning a normal bilirubin does NOT exclude perforation 3

• CRP is superior to bilirubin for anticipating perforation, with 98% of perforated cases showing elevated CRP versus only 38% showing hyperbilirubinemia 8

• CT findings (extraluminal appendicolith, abscess, extraluminal air, wall enhancement defect, periappendiceal fat stranding) are far more accurate than any laboratory marker for identifying complicated appendicitis 1, 7

Common Pitfalls to Avoid

• Do not delay imaging to "wait and see" if bilirubin rises further—this wastes time and risks perforation 6, 7

• Do not use bilirubin elevation to justify proceeding directly to surgery without imaging, as the positive predictive value is only 85% and you may miss alternative diagnoses 2, 3

• Do not reassure yourself that appendicitis is less likely because bilirubin is only mildly elevated—26% of appendicitis cases have normal bilirubin 3

• Do not order liver enzymes to "work up" the hyperbilirubinemia in this acute setting—they are typically normal or marginally elevated in appendicitis and add no diagnostic value 5

Bottom Line

Treat this patient exactly as you would any patient with suspected appendicitis and similar clinical features (fever, leukocytosis, RLQ pain)—the mildly elevated bilirubin is an incidental finding that should not influence your management. 1, 6 Order CT with IV contrast now, and if positive, proceed to antibiotics and surgery. 6, 7