Pancreatic Function Tests

Written by Iris Levink

Faecal Elastase-1

Faecal elastase-1 is produced exclusively in the pancreas and unsusceptible to intestinal breakdown, making it reflect the pancreatic secretory capacity. Faecal elastase-1 concentration is assessed by stool sample analysis. Preferably mid- to solid samples are used, as diarrheal or watery stools dilute the faecal elastase-1 concentration, leading to less accurate results.^1-4 A faecal elastase-1 concentration of <200 mcg/g is deemed abnormal, levels <100 mcg/g suggest pancreatic exocrine insufficiency and levels between 100 and 200 mcg/g are indeterminate. While it is a reliable screening method for severe pancreatic exocrine insufficiency, it is less sensitive to diagnose mild pancreatic exocrine insufficiency.² The sensitivity of faecal elastase-1 in detecting mild, moderate and severe pancreatic exocrine insufficiency is reported to be 63%, 100% and 100%, respectively.⁵Given its widespread availability and non-invasive nature, faecal elastase-1 is the diagnostic test of choice in clinical settings.^4,6,7

Coefficient of fat absorption

Coefficient of fat absorption (CFA) evaluates fat maldigestion by measuring faecal fat excretion over a 72-hour period after a given fat intake. While it quantifies fat absorption, it does not specifically diagnose pancreatic exocrine insufficiency.^1,4 Instead, steatorrhea, defined as 24-hour fecal fat excretion of 7 grams or more, serves as an indicator of malabsorption, which may be caused by pancreatic exocrine insufficiency. Given this test is also cumbersome, it is not routinely used to diagnose pancreatic exocrine insufficiency.

Faecal Chymotrypsin

This enzymatic test measures chymotrypsin in faecal samples. Compared to faecal elastase-1, its specificity is considerably lower (49% for mild pancreatic exocrine insufficiency and 85% for severe pancreatic exocrine insufficiency), and accurate measurements require temporary enzyme discontinuation.⁵

Breath Tests

A 13C breath test offers a non-invasive method to assess fat malabsorption by measuring the intestinal breakdown of a labelled fatty substrate. It involves ingesting a 13C-marked meal, which undergoes hydrolysis in the intestinal lumen in proportion to pancreatic lipase activity.^2,4 The resulting hydrolysed products are absorbed, metabolised and released as 13-CO2 through the pulmonary endothelium. This process is quantified by exhalation of 13-CO2, using mass spectrometry or infrared analysis. The use of this test is limited by a lack of sensitivity and specificity, especially in mild pancreatic exocrine insufficiency.^2,4,5

Serum Trypsinogen

Serum trypsinogen levels provide insight into pancreatic acinar cell mass. Again, this test exhibits a high sensitivity for severe pancreatic exocrine insufficiency (levels below 20 ng/mL) but lower sensitivity in mild cases (ranging from 20 to 29 ng/mL). It is therefore not commonly used in clinical practice.¹

Direct measurement

Direct measurements provide the most accurate diagnosis of pancreatic exocrine insufficiency but are invasive, time-consuming and can cause patients discomfort. These methods involve inducing pancreatic secretion by administration of cholecystokinin (CCK) or secretin, followed by the collection of duodenal fluid for analysis. The assessment includes volume, enzyme concentration and bicarbonate output. A bicarbonate concentration of <80 m Eq/L in all samples is indicative of a pancreatic exocrine insufficiency diagnosis.Given the complexity of indirect testing, it is generally reserved for research settings.^1,2,5

References

Capurso G, et al. Clin Exp Gastroenterol. 2019;12:129-139.
Whitcomb DC, et al. Gastroenterology. 2023;165(5):1292-1301.
Barkin JA, et al. Pancreas. 2024;53(1):e16-e21.
Dominguez-Muños JE, et al. United European Gastroenterology Journal. 2024 Dec 5.
Löser C, et al. Gut. 1996 Oct;39(4):580–586.
Tyler Stevens, Darwin L Conwell. November 8th, 2023. Accessed March 2024. https://www.uptodate.com/contents/exocrine-pancreatic-insufficiency#H2482574495
Lan X, et al. Cancers (Basel). 2023 Feb 20;15(4).