Performance evaluation of a smartphone-based home test for fecal calprotection.

Objectives: Fecal calprotectin (FC) serves as a non-invasive marker for the assessment of gut inflammation in patients with inflammatory bowel disease (IBD). Laboratory measurements are usually performed with immunologic methods like enzyme-linked immunosorbent assay. Recently, quantitative home tests based on the lateral flow technology with smartphones as read-out devices have been developed. We compared the quantitative and qualitative performance of the quantitative lateral flow home test Preventis SmarTest^® Calprotectin Home and the immunological test used in our laboratory (Eurospital Calprest^® Turbo).

Methods: Fourty-five routine samples were analyzed in parallel with both tests according to the manufacturer's instructions. The read-out of the home test was performed with two smartphones (Apple iPhone 14 Pro and Samsung Galaxy XCover 5). The qualitative interpretation (positive, negative, borderline) was conducted using the cut-offs provided by the manufacturers.

Results: Statistically significant correlations with the laboratory standard method were observed for both smartphones (Spearman's rho 0.703 and 0.715, all p<0.005). The home test showed systematically higher concentrations compared to the routine assay. We found minimal qualitative agreement between the two tests (Cohen's kappas (κ)=0.323 and 0.300; p=0.003 and 0.005) showing a lower rate of positives with the home test. Both used smartphones showed good quantitative and qualitative agreement.

Conclusions: The tests are quantitatively not interchangeable. However, the home test may be applicable for the serial follow-up management of patients with IBD. The higher rate of samples classified as negative with the home test may lead to an underestimation of affected patients.