Alison Jones, Consultant Clinical Biochemist, York and Scarborough NHS Foundation Trust
It is well documented that liquid/watery stool samples should not be tested for faecal elastase due to the risk of a false low result suggesting pancreatic insufficiency (a false positive). This is not a failure of the assay – it works in exactly the same way whether the sample is formed or liquid. The challenge is more in the interpretation of the result. Is the low result due to a poorly pancreas, or is it the body’s reaction to some other pathology causing dilution of the elastase in an individual with an otherwise functioning pancreas?
Although I understand the reasons, taking a hard line on samples and rejecting liquid ones isn’t overly helpful. In the main I would suggest that elastase testing comes from secondary care settings where patients are more likely to have longer term gastric issues who might never produce a more formed sample. Even if the patient does have pancreatic insufficiency, it is often associated with diarrhoea!
So, is there an alternative?
Alison Jones (Consultant Clinical Biochemist) from York and Scarborough NHS Foundation Trust discuss a recent audit conducted, and the recommendations that have been implemented.
The reason we started the project was based on an anecdotal feeling that we were getting a lot of watery samples that weren’t being repeated despite reporting the results with comments suggesting the result may be unreliable.
We retrospectively reviewed three years (2018 – 2020) of elastase results, which comprised just over 5000 tests, and 5.7% of these (288 samples) were identified as watery1. We then identified if we had received a formed sample from the same patient to try and validate the result from the liquid sample – not a technically accurate method, but the only basis we had to compare.
