72 Hour Quantitative Fecal Fat: Optimal Testing Recommendations
Also known as: 72 hour stool lipids, quantitative
- A 72 hour timed quantitative fecal fat measurement is not indicated in the differentiation of pancreatic diseases and should be used with caution in the evaluation of malabsorption.
- Although referenced as a gold standard for the diagnosis of malabsorption, often, results from 72 hour quantitative fecal fat testing do not provide significant clinical value, and test results do not provide additional information on the causation of malabsorption.
- 72 hour quantitative fecal fat test results are highly sensitive to pre-analytical considerations (i.e., dietary requirements), which may significantly impact the test interpretation.
Guidelines for Test Utilization
What does the test tell me?
A timed (72 hour) quantitative fecal fat test may be used to determine increased fat excretion in stool (also called steatorrhea) and may be suggestive of malabsorption. Dietary fat intake records may be required to assist in test interpretation. [back to top]
When should I order this test?
Due to the significant challenges regarding the collection and analysis of a timed stool sample, a 72 hour quantitative fecal fat should be used with caution in the evaluation of malabsorption, including in pediatric and/or adolescent patients who have frequent loose stools or if there is a clinical suspicion of eating disorders. [back to top]
When should I NOT order this test?
Do not order this test to screen for malabsorption, to diagnose the etiology of malabsorption, or to differentiate amongst pancreatic disease states (including chronic pancreatitis, cystic fibrosis, cancer). [back to top]
How should I interpret the result?
A 72 hour quantitative fecal fat result of greater than 7 grams of fat per day may be suggestive of malabsorption, but does not diagnosis the cause of aberrant absorption. Steatorrhea, or increased fat in the stool, may occur in the background of bacterial overgrowth, short bowel syndrome, small bowel mucosal diseases such as Crohn disease or celiac disease, or pancreatic exocrine insufficiency. Due to dietary and collection considerations, a 72 hour quantitative fecal fat result of less than 7 grams of fat per day does not exclude potential steatorrhea or malabsorption. [back to top]
Is the test result diagnostic/confirmatory of the condition? If not, is there a diagnostic/confirmatory test?
72 hour fecal fat quantitation is suggestive of malabsorption. This testing does not provide additional information on the source of malabsorption. Based on clinical presentation, more appropriate laboratory testing is indicated to identify the underlying disease state. For example, fecal elastase-1 has been utilized in the evaluation of pancreatic exocrine insufficiency in both adults, as well as children with cystic fibrosis. Fecal elastase-1 measurements (less than 15 micrograms/gram stool in cystic fibrosis patients and less than 200 microgams/gram stool in adults) are indicative of pancreatic exocrine insufficiency. Fecal elastase-1 is also associated with a high negative predictive value in ruling out pancreatic exocrine insufficiency. [back to top]
Are there factors that can affect the lab result?
There are a number of patient-specific factors that can affect laboratory results. Patients must be on a fat-controlled diet of greater than 100 grams of fat per day for several days prior to sample collection. Inadequate ingestion of sufficient fat in the diet or incomplete sample collection may result in falsely negative results. It is recommended that dietary intake records are provided to ensure appropriate dietary fat intake during sample collection.
The use of laxatives, synthetic fat substitutes, fat-blocking nutritional supplements, or mineral oils prior to and during collection of stool samples may lead to falsely elevated results. The use of suppositories, administration of barium contrast prior to sample collection, or sample contamination with diaper rash ointment can also invalidate test results. Lastly, fecal fat excretion may be increased in the background of diarrhea and the absence of malabsorption. [back to top]
Are there considerations for special populations?
In children with cystic fibrosis and on pancreatic enzyme replacement therapy, supplements must be discontinued prior to testing. This test should not be performed in individuals who are taking fat-blocking medications (i.e., Orlistat) or mineral oil supplementation. This test can also be impacted in individuals who have known gastrointestinal co-morbidities (i.e., gastric bypass, short bowel syndrome). Lastly, reference ranges for 72 hour fecal fat quantitative testing may differ between adult and pediatric populations. [back to top]
What other test(s) might be indicated?
There is limited use for 72 hour quantitative fecal fat testing in the evaluation of malabsorption, and it is not indicated in the differentiation of pancreatic disease states. Based on clinical presentation, more targeted laboratory testing may be performed to identify the underlying pathology associated with suspected malabsorption. [back to top]
Rifai N, Horvath AR, Witwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics, 6th ed. St Louis, MO: Saunders Elsevier; chapter 62. 2017.
Vanga RR, Tansel A, Sidiq S, El-Serag HB, Othman M. Diagnostic Performance of Measurement of Fecal Elastase-1 in Detection of Exocrine Pancreatic Insufficiency: Systematic Review and Meta-analysis. Clin Gastroenterol Hepatol. 2018 Jan 31. [Epub ahead of print]
Cystic Fibrosis Trust. Standards for the clinical care of children and adults with cystic fibrosis in the UK. Bromley 2001. (http://www.cysticfibrosis.org.uk/media/448939/ cd-standards-ofcare-dec-2011.pdf)
Hill PG. Faecal fat: time to give it up. Ann Clin Biochem. 2001; 38:164-167.
Last reviewed: June 2020. The content for Optimal Testing: AACC's Guide to Lab Test Utilization has been developed and approved by the AACC Academy and AACC's Science and Practice Core Committee.
As the fields of laboratory medicine and diagnostic testing continue to grow at an incredible rate, the knowledge and expertise of clinical laboratory professionals is essential to ensure that patients received the highest quality and most useful laboratory tests. AACC's Academy and Science and Practice Core Committee have developed a test utilization resource focusing on commonly misused tests in hospitals and clinics. Improper test utilization can result in poor patient outcomes and waste in the healthcare system. This important resource geared toward medical professionals recommends better tests and diagnostic practices. Always consult your laboratory director to make sure these recommendations are appropriate for your patient population.