Abstract
BACKGROUND: Accurate measurement of phenylalanine (Phe) is a requirement for the diagnosis and management of individuals with Phenylketonuria (PKU). The current methods for quantifying Phe, plasma amino acids, and dried blood spots (DBS) have several analytical limitations and are not suitable for self-monitoring. This study evaluated the validity of a point-of-care testing (POCT) device, the Egoo Phe Test, in a sample of females with PKU who participated in a five-day camp intervention. METHODS: Blood samples were collected from 20 participants (median age: 18 years; IQR: 16, 28.3) on the first (day 1) and/or final (day 5) day of camp for Phe quantification by plasma amino acids, DBS, and the Egoo Phe Test. Phe concentrations determined by these three methods were compared to assess agreement. RESULTS: On both days of camp, strong positive agreement based on Lin's concordance correlation coefficient (p(c)) was found between Egoo and DBS (day 1: p(c) = 0.91 [95% CI: 0.78, 0.96]; day 5: p(c) = 0.91 [95% CI: 0.79, 0.96]) and moderate positive agreement was identified between Egoo and plasma amino acids (day 1 p(c) = 0.80 [95% CI: 0.63, 0.89]; day 5 p(c) = 0.83 [95% CI: 0.68, 0.91]). Phe concentrations measured by the Egoo were lower than Phe concentrations determined by plasma amino acids (day 1 average difference: -31.2% [95% CI: - 40.2, - 25.8]; day 5 average difference: -12.4% [95% CI: -30.4, - 4.2]) and higher than DBS (day 1 average difference: 16.2% [95% CI: 4.6, 25.3]; day 5 average difference: 12.2% [95% CI: - 1.4, 20.5]). When assessing pairwise differences between the methods for each sample, > 66.7% of the Egoo Phe results were within ± 20% difference of the DBS values on day 5 of camp. However, this criterion was not met when comparing Egoo with DBS on day 1 of camp or with plasma amino acids on either day of camp. CONCLUSIONS: The Egoo Phe Test demonstrated potential as a substitute for DBS, but additional research in larger and more diverse clinical cohorts is required. Future research should focus on improving accuracy and defining analytical targets that consider the clinical impact of Phe test performance on management of patients with PKU. CLINICAL TRIAL NUMBER: not applicable.