Assessment of steatorrhoea

Steatorrhoea, an excess of fat in stools, indicates a problem with either fat digestion or fat absorption. There are few descriptive studies on steatorrhoea outside of patients with pancreatic disease. Other recognised causes of steatorrhoea include diseases associated with bile acid deficiency states and small intestinal malabsorption.

Normal fat absorption

Normal fat absorption involves a complex mixture of digestive enzymes, bile salts, and an intact intestinal mucosa to enable uptake of these hydrophobic complexes. After ingestion, dietary lipids are initially emulsified in the stomach and then hydrolysed by the action of gastric and pancreatic lipase and colipase. The hydrolysed lipids are then aggregated into micelles or liposomes with the addition of bile salts in the duodenum and jejunum.[1]Ros E. Intestinal absorption of triglyceride and cholesterol. Dietary and pharmacological inhibition to reduce cardiovascular risk. Atherosclerosis. 2000;151:357-379. http://www.ncbi.nlm.nih.gov/pubmed/10924713?tool=bestpractice.com These micelles are absorbed across the intact intestinal villi by both active and passive processes. Finally, they are packaged into chylomicrons within intestinal epithelial cells and transported to the circulation via the lymphatic system.[2]Black DD. Development and physiological regulation of intestinal lipid absorption. I. Development of intestinal lipid absorption: cellular events in chylomicron assembly and secretion. Am J Physiol Gastrointest Liver Physiol. 2007;293:G519-G524. http://www.ncbi.nlm.nih.gov/pubmed/17495031?tool=bestpractice.com

More than 90% of daily dietary fat is absorbed into the general circulation.[3]Bashaw H, Brownell JN, Schall JI, et al. Measures of dietary fat and energy absorption in healthy adults. Pancreas. 2020 Jul;49(6):845-54. http://www.ncbi.nlm.nih.gov/pubmed/32590620?tool=bestpractice.com Defects in the processes that comprise dietary fat absorption can reduce uptake and lead to steatorrhoea.

Categories of steatorrhoea

Patients with steatorrhoea can be considered in 3 broad aetiological categories.

• Pancreatic exocrine insufficiency. These patients have insufficient lipase and colipase to allow normal lipid hydrolysis. This most commonly occurs due to chronic pancreatic inflammation and loss of acinar cells.

• Bile salt deficiency due to impaired production or secretion, or reduced circulating bile acids.

• Malabsorption due to small intestinal disease, surgery, or medications.