Diagnosis: Acute Hepatitis B Infection
The diagnosis is acute hepatitis B infection (option c), based on the presence of HBsAg positive, anti-HBc IgM positive, and anti-HBs negative—a serologic profile that definitively indicates acute HBV infection according to CDC case definitions. 1, 2
Serologic Profile Analysis
The patient's laboratory results demonstrate the classic triad for acute hepatitis B:
- HBsAg positive indicates active HBV infection and is the first detectable marker appearing 1-10 weeks after exposure 2, 3
- Anti-HBc IgM positive is the most reliable marker for distinguishing acute from chronic HBV infection, appearing at symptom onset and persisting for up to 6 months in resolving acute infection 1, 2, 3
- Anti-HBs negative confirms this is not a resolved infection or vaccination response 2
This exact serologic pattern (HBsAg+, IgM anti-HBc+, anti-HBs-) is specifically defined by the CDC as diagnostic of acute hepatitis B infection 1, 2.
Why Other Diagnoses Are Excluded
Acute Hepatitis C (Option b) - Ruled Out
- While anti-HCV is positive, HCV RNA is undetectable, which excludes active hepatitis C infection 1
- The CDC criteria for acute hepatitis C require elevated aminotransferases with anti-HCV positive and HBsAg negative or IgM anti-HBc negative—this patient has both HBsAg and IgM anti-HBc positive 1
- The positive anti-HCV likely represents past resolved HCV infection or a false positive in the setting of acute HBV 1
Alcoholic Hepatitis (Option d) - Ruled Out
- The AST:ALT ratio is 0.57 (300:525), which is inverted from the typical 2:1 ratio seen in alcoholic hepatitis 2
- The marked elevation of ALT (525) far exceeds what is typically seen in alcoholic hepatitis, where transaminases rarely exceed 300 U/L 2
- The serologic markers definitively establish viral hepatitis B as the etiology 1
Acute Autoimmune Hepatitis (Option a) - Ruled Out
- ANA titer of 1:40 is too low to suggest autoimmune hepatitis, which typically requires titers ≥1:80 or preferably ≥1:160 2
- The positive IgM anti-HBc establishes acute HBV as the primary diagnosis 1, 2
- Autoimmune hepatitis does not present with HBsAg positivity 2
Clinical Context Supporting Acute HBV
The patient's presentation aligns perfectly with acute hepatitis B:
- Risk factors: IV drug use history provides clear exposure route for HBV transmission 1, 2
- Clinical symptoms: Fatigue, jaundice, and abdominal pain over one week with low-grade fever (99.9°F) match the typical 2-4 month acute illness course 2
- Physical findings: Icteric sclera, hepatomegaly with tenderness, and absence of ascites are consistent with acute rather than chronic liver disease 2
- Laboratory pattern: Total bilirubin 8.0 mg/dL with markedly elevated transaminases (ALT 525, AST 300) indicates acute hepatocellular injury 1, 2
Critical Management Implications
- No specific antiviral treatment is indicated for acute hepatitis B; supportive care is the standard approach 2
- Monitor for acute liver failure, which occurs in approximately 1% of acute HBV cases—watch for coagulopathy, encephalopathy, or worsening synthetic function 2
- Follow-up serologies at 6 months to confirm resolution versus progression to chronic infection (HBsAg persistence >6 months defines chronicity) 1, 3
- Screen and vaccinate contacts: Test all household and sexual contacts for HBsAg and anti-HBs, vaccinating seronegative individuals immediately 2, 4
- Counsel on transmission prevention: Avoid alcohol completely, cover wounds, practice safe sex, and do not share needles or personal items 1, 2
Important Pitfall to Avoid
The positive anti-HCV with undetectable HCV RNA should not distract from the clear diagnosis of acute hepatitis B. Up to 20% of acute hepatitis C cases are anti-HCV negative at presentation due to delayed seroconversion, but this patient has undetectable HCV RNA, definitively excluding active HCV infection 1. The anti-HCV positivity likely represents either past resolved infection or a false positive in the context of acute viral hepatitis 1.