Real-Life Application of a Point-of-Care Biosensor for Phenylalanine in Patients With Phenylketonuria.

Phenylketonuria (PKU) is a rare metabolic disorder causing elevated phenylalanine (PHE) levels requiring lifelong dietary or pharmacological management and regular monitoring. Current PHE monitoring methods, such as tandem mass spectrometry (FIA-MS/MS), are laboratory and sample transport-dependent, leading to delays in obtaining results. This highlights the need for accessible point-of-care (PoC) solutions. Building on a previously developed bioluminescence-based PHE quantification method, we created a PoC PHE sensor integrated with a smartphone app (phenyx app) for real-time monitoring and data sharing. In a clinical study with PKU patients, we evaluated the reliability of the sensor and the app by comparing at-home PHE measurements with dried blood samples (DBS) analyzed using the gold standard FIA-MS/MS. We also assessed time differences between sampling and results, sensor practicality, and user experience. Forty-seven PKU patients (median age 10.0 years, range 0.7-53.4) performed one supervised and four at-home measurements using the PHE sensor, alongside DBS sampling for FIA-MS/MS. The sensor showed higher PHE values than FIA-MS/MS, with a mean difference of 84.8 μmol/L (p = 0.0017). Variability was influenced by test supervision (clinic vs. home) and test kit age (greater difference in older batches, p = 0.001). Usability of the PHE sensor and phenyx app was rated favorably; all patients preferred the PHE sensor over laboratory testing. PoC measurement using the PHE sensor and phenyx app is feasible, reliable, and provides rapid results comparable to FIA-MS/MS, representing a key step toward patient self-testing. Trial Registration: NCT05998109, NCT06940193, DRKS00031972.