What is the most likely diagnosis and recommended management for a 20‑year‑old man with markedly elevated aminotransferases, total bilirubin 5.9 mg/dL (direct 2.9 mg/dL) and a positive heterophile antibody test for infectious mononucleosis?

Infectious Mononucleosis with Hepatic Involvement

This is infectious mononucleosis (IM) with hepatic involvement, and management is entirely supportive—no specific treatment is required for the elevated liver enzymes or bilirubin, which will resolve spontaneously over 6–12 weeks. 1, 2

Diagnosis Confirmation

The combination of a positive heterophile antibody test (monospot), markedly elevated aminotransferases, and conjugated hyperbilirubinemia (direct bilirubin 2.89 mg/dL representing ~49% of total) in a 20-year-old male establishes the diagnosis of infectious mononucleosis with hepatic involvement. 1, 3

• The heterophile antibody test has 87% sensitivity and 91% specificity for IM, making it the diagnostic standard in this age group. 1
• Elevated liver enzymes increase clinical suspicion for IM even when the heterophile test is negative, but in this case both are positive, confirming the diagnosis. 1
• Approximately 57–62% of IM patients have elevated AST/ALT, and 16% develop hyperbilirubinemia, so this presentation is typical rather than concerning. 2

Pattern of Liver Injury

The conjugated hyperbilirubinemia (direct bilirubin >35% of total at 49%) indicates hepatocellular injury rather than simple Gilbert syndrome. 4

• This mixed hepatocellular-cholestatic pattern is characteristic of EBV hepatitis, which occurs in the majority of IM cases. 2
• Clinical hepatomegaly occurs in approximately 10% of IM patients, though subclinical hepatic involvement is far more common. 3, 2
• The bilirubin level of 5.9 mg/dL, while elevated, is well below the threshold that would suggest alternative diagnoses or complications. 2

Management Approach

Treatment is entirely supportive—no antiviral therapy, corticosteroids, or specific hepatic interventions are indicated for uncomplicated IM with elevated liver enzymes. 1, 3

Immediate Management

• Advise reduction of activity and bed rest as tolerated; patients should avoid contact sports or strenuous exercise for 8 weeks from symptom onset due to splenic rupture risk (0.1–0.5% incidence). 3, 1
• No routine abdominal ultrasound is required for subclinical LFT derangement in immunocompetent IM patients, as there are no reports of decompensated liver disease in this population. 2
• Routine use of corticosteroids is not recommended for uncomplicated IM, even with significant hepatic involvement. 1

Monitoring Strategy

• Serial liver function testing is not required in immunocompetent patients with subclinical LFT derangement. 2
• Median time to LFT resolution is 8 weeks (range 6–12 weeks), with maximum resolution time exceeding 6 months in some cases. 2
• If you choose to monitor, repeat testing at 8–12 weeks is reasonable to document resolution, but earlier serial testing provides no clinical benefit. 2

What NOT to Do

• Do not order abdominal ultrasound to evaluate the elevated bilirubin or transaminases—current evidence shows no benefit in immunocompetent IM patients. 2
• Do not pursue extensive hepatobiliary workup (MRCP, liver biopsy, autoimmune serologies) for isolated IM-related hepatitis. 2
• Do not prescribe antiviral medications (acyclovir, valacyclovir), as they have no proven benefit in acute IM. 1
• Do not use ampicillin or amoxicillin for any concurrent pharyngitis, as 90–100% of IM patients develop a characteristic maculopapular rash with these antibiotics. 3

Expected Clinical Course

• Fatigue may be profound but tends to resolve within 3 months in most patients. 3
• Fever, pharyngitis, and lymphadenopathy typically resolve within 2–4 weeks, while hepatic enzyme abnormalities lag behind clinical improvement. 3, 2
• The patient should be counseled that IM is a risk factor for chronic fatigue syndrome, which develops in a subset of patients. 3

Red Flags Requiring Reassessment

• Progressive jaundice, pruritus, or bilirubin >15 mg/dL would be atypical for IM and warrant investigation for alternative diagnoses (drug-induced liver injury, autoimmune hepatitis, biliary obstruction). 5, 4
• Development of coagulopathy (elevated INR) or hypoalbuminemia suggests hepatic synthetic dysfunction and requires urgent hepatology consultation. 5, 4
• Persistent LFT elevation beyond 6 months warrants complete hepatobiliary evaluation including viral hepatitis serologies, autoimmune markers, and consideration of liver biopsy. 5, 2

Patient Counseling

• Reassure the patient that elevated liver enzymes and bilirubin are expected in IM and will resolve spontaneously without treatment. 2
• Emphasize strict avoidance of contact sports and heavy lifting for 8 weeks to prevent splenic rupture, the most feared complication. 3, 1
• Advise gradual return to normal activity using shared decision-making after the 3-week minimum restriction period. 1