Gastroenterology and Hepatology
Liver biochemistry patterns
Separate hepatocellular injury (ALT/AST predominant, over 1000 IU/L in paracetamol toxicity, viral hepatitis or ischaemia) from cholestatic injury (ALP and GGT predominant: obstruction, PBC, PSC, drugs). Remember that ALT is not a liver function test - synthetic function is judged by bilirubin, INR and albumin.
Ascites and its complications
Always perform a diagnostic tap. The serum-ascites albumin gradient (SAAG) is at least 11 g/L in portal hypertension (cirrhosis, cardiac failure) and below 11 g/L in exudative causes such as peritoneal malignancy or tuberculosis. An ascitic neutrophil count above 250/mm3 defines spontaneous bacterial peritonitis - treat with a third-generation cephalosporin plus albumin. In acute variceal bleeding give terlipressin and prophylactic antibiotics with endoscopic band ligation.
Hepatitis B serology
HBsAg indicates current infection; isolated anti-HBs indicates vaccination or past clearance; IgM anti-HBc indicates acute infection or a flare; HBeAg indicates high replication.
Gut
Ulcerative colitis is continuous, rectal-first, with pANCA; Crohn disease is patchy with granulomas, fistulae and ASCA. Acute pancreatitis is usually gallstone- or alcohol-related; give fluids, analgesia and early ERCP if there is cholangitis. Test anti-tTG IgA with total IgA for coeliac disease.
Trap: assuming a normal ferritin excludes iron deficiency in inflammation, and forgetting that cholestatic liver tests need an ultrasound.
Rule of thumb: SAAG = serum albumin minus ascitic albumin; a gradient of 11 g/L or more means portal hypertension.