Laboratory markers of hepatic and pancreatic function and malabsorption

Role

Laboratory markers of hepatic and pancreatic exocrine insufficiency help distinguish malabsorption from these two organ systems from small bowel mucosal causes (e.g. coeliac disease), each pointing toward a different diagnostic and management pathway
Relevant whenever malabsorption (steatorrhoea, weight loss, fat-soluble vitamin deficiency) is being investigated, since hepatic and pancreatic causes require different confirmatory tests and treatments from mucosal small bowel disease

Pancreatic exocrine insufficiency - reduced secretion of lipase/other digestive enzymes causes fat maldigestion (distinct from malabsorption at the mucosal level) - faecal elastase-1 is the standard non-invasive screening test (reduced in exocrine insufficiency, unaffected by concurrent enzyme replacement therapy, making it useful even in patients already on treatment)
Hepatic/biliary causes of fat malabsorption relate to reduced bile acid delivery to the gut lumen (cholestasis, biliary obstruction) - impairing fat emulsification necessary for lipase action, distinguished by cholestatic LFT pattern (raised ALP/GGT/bilirubin) alongside the malabsorption picture

Faecal elastase-1 <200 microg/g suggests pancreatic exocrine insufficiency (levels <100 suggest severe insufficiency); a normal result makes clinically significant pancreatic insufficiency unlikely
Faecal fat quantification (72-hour collection) is the gold-standard confirmatory test for steatorrhoea generally but does not itself distinguish the specific cause (pancreatic, hepatic/biliary, or mucosal) - it confirms fat malabsorption is present, prompting further targeted workup
Distinguishing the pattern (isolated fat malabsorption favouring pancreatic/biliary cause vs broader malabsorption including protein/carbohydrate/micronutrients favouring a mucosal small bowel cause) guides which further test to pursue next

Confirmed pancreatic exocrine insufficiency -> pancreatic enzyme replacement therapy (PERT), with faecal elastase testing remaining valid for monitoring given it is unaffected by exogenous enzyme supplementation
Confirmed cholestatic/biliary cause -> investigate and treat the specific biliary/hepatic pathology (see liver disease and MRI/MRCP)

Chronic pancreatitis, cystic fibrosis (pancreatic insufficiency), coeliac disease and other mucosal causes (the key differential), cholestatic liver disease/biliary obstruction

Faecal elastase-1's stability in the presence of exogenous pancreatic enzyme supplementation is a specifically useful, testable feature - it can be used to confirm the original diagnosis and assess severity even in a patient already established on enzyme replacement therapy, unlike some other pancreatic function tests

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