A New ERA of Blood Phenylalanine Monitoring

Background: In phenylketonuria (PKU) patients, dried blood spot (DBS) sampling remains the standard method for monitoring phenylalanine (Phe) levels. However, delays in reporting results can hinder timely dietary adjustments. Patients and caregivers have expressed a preference for point-of-care testing (POCT) devices that enable home-based monitoring. Objectives: Our aim was to compare blood Phe measurements in PKU patients and caregiver usability of a POCT system with DBS, which is the standard practice monitoring method. Methods: Twenty participants (eighteen children with PKU and two healthy controls) were recruited. Caregivers of children with PKU were asked to perform blood Phe measurements at home under the supervision of a researcher, using both the POCT device (Egoo Phe system) and DBS sampling. Healthy controls collected the same number of samples using both methods in a hospital setting. The POCT system required 40 µL of blood and used an enzymatic, bioluminescent detection system. DBS samples were analyzed by tandem mass spectrometry (TMS) and required two blood spots (approximately 100 µL of blood). The Egoo Connect App, linked via Bluetooth to the POCT device, displayed results after 29 min. Caregiver usability of the POCT system was assessed using questionnaires at each visit. Results: A total of 100 paired samples were collected. Median values were 274 μmol/L (range: 30–1039) for POCT and 270 μmol/L (range: 20–1190) for DBS. POCT readings were a mean of 4.6% higher than DBS with a noticeable strong correlation observed (y = 1.017x; R2 = 0.8450; p < 0.0001). The usability of the POCT system improved with caregiver practice, and all caregivers expressed a preference for POCT over DBS. Conclusions: The POCT system for blood Phe demonstrated strong concordance with DBS and high caregiver acceptance, highlighting its potential to transform PKU care through faster, patient-driven monitoring and more timely clinical decision-making.