IM5.11-14 | Liver Disease Diagnostic Testing — Summary & Reflection

KEY TAKEAWAYS

Diagnostic testing in liver disease requires four skills:

1. LFT interpretation (IM5.11, IM5.13): Identify the pattern — hepatocellular (ALT/AST dominant), cholestatic (ALP/GGT dominant), mixed, or isolated hyperbilirubinaemia. Assess synthetic function (albumin, INR) independently. Calculate AST:ALT ratio (>2:1 with alcohol = ALD). Use the pattern to branch the investigation pathway.

2. Hepatitis serology (IM5.11): HBsAg = current HBV infection. Anti-HBc IgM = acute HBV (window period diagnostic). HBeAg = high replication, infectivity. HBV DNA = gold standard for replication. Anti-HCV screen → HCV RNA to distinguish active from past infection. No HCV antigen-based serology distinguishes acute from chronic — duration established by clinical timeline.

3. Ascitic fluid analysis (IM5.14): SAAG = serum albumin − ascites albumin (same-day samples). SAAG ≥1.1 = portal hypertension; <1.1 = non-portal (TB, malignancy, pancreatitis). PMN ≥250/mm³ = SBP — treat empirically immediately. Bedside inoculation into blood culture bottles increases culture yield.

4. Imaging selection (IM5.12): Ultrasound first (echotexture, duct dilatation, focal lesions, portal hypertension features). Cholestatic + dilated duct → MRCP (diagnostic) or ERCP (therapeutic). Focal lesion in cirrhotic → CT triphasic (arterial enhancement + portal washout = HCC). FibroScan for non-invasive fibrosis staging. ERCP is therapeutic, not diagnostic — use after MRCP has mapped the anatomy.

REFLECT

Return to the hook scenario: bilirubin 4.8 mg/dL, ALT 1,240, AST 610, ALP 180, albumin 3.2, INR 1.6; ascitic fluid PMN 180, protein 12 g/L, albumin 4 g/dL (serum albumin needed to complete SAAG). The LFT pattern is hepatocellular (ALT/AST dominant, ALP not markedly elevated). AST:ALT ratio = 610/1,240 ≈ 0.5 — less than 1, arguing against alcoholic liver disease. The synthetic function is partially impaired (albumin 3.2, INR 1.6 — borderline). Ascitic PMN 180/mm³ is below the SBP threshold of 250 — SBP not confirmed, but close enough that the clinical picture must be watched closely. Now: what is your leading aetiological diagnosis given AST:ALT <1? What is the single most important next investigation? And would you start antibiotics tonight, or wait for the culture? Write down your answers before looking them up — this is the self-directed component of your learning that no module can substitute for.