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.