P374 Home or hospital-based analysis of stool calprotectin: assessing two methods for monitoring inflammatory bowel disease
Heida A.*1, Knol M.1, Muller Kobold A.2, Dijkstra G.3, van Rheenen P.1
1University Medical Center Groningen, Pediatric Gastroenterology, Groningen, Netherlands 2University Medical Center Groningen, Laboratory Medicine, Groningen, Netherlands 3University Medical Center Groningen, Department of Gastroenterology and Hepatology, Groningen, Netherlands
For 8 years we have been following patients with inflammatory bowel disease by periodically measuring calprotectin levels in their sent-in stool samples with an enzyme-linked immunosorbent assay (ELISA). Levels below 250 μg/g confirmed disease remission, levels above 500 μg/g indicated a disease flare, and indecisive values between 250 and 500 μg/g required retesting after 1 month. Physicians and patients found repeated testing of calprotectin helpful to guide therapy, but both wished to receive the results without delay. BÜHLMANN Laboratories recently developed a lateral flow-based calprotectin test and a software application (IBDoc®) that turns an ordinary smartphone camera into a reader for quantitative measurements at home. We compared this new method with the established ELISA method to see whether they agreed sufficiently for the new to replace the old, or to use the two interchangeably.
Eligible teenagers and adults, who had a smartphone validated for the IBDoc® app, received an instruction manual to perform the calprotectin stool test at home. The residual of the stool specimen was sent to the hospital for ELISA measurement of calprotectin. Agreement between methods was assessed, as well as critical misclassifications of disease activity (leading to over- or undertreatment). Predefined acceptable limits of agreement were ±100 μg/g in the lower ranges of calprotectin and ±200 μg/g in the higher ranges.
85 participants produced 152 paired calprotectin measurements. In the lower ranges (i.e., between 40 and 400 μg/g) 99 of 117 pairs (85%) were within acceptable limits of agreement, and in the higher ranges (>400 μg/g) 20 of 35 pairs (57%). Eighty percent of all paired measurements were concordant (Figure 1). Critical misclassification (disease remission with one method and disease flare with the other) was observed in 4% of pairs. Two critical misclassifications leading to undertreatment (low IBDoc®, high ELISA) were in fact invalid measurements by a single patient who continued the analytical step before the indicated incubation period.
We found acceptable agreement between IBDoc® home test and hospital-based ELISA in the critical lower ranges of calprotectin and therefore the new method can be used to monitor patients in remission. Results in the higher range need to be confirmed before therapy adjustment. Misclassification can probably be further reduced with a face-to-face training of the patients.