FIGURE 1.

Phenylalanine loading test. A total of 6.5 gm (100 mg/kg, based on weight of 65 kg) of phenylalanine was mixed with apple juice. Fingerstick blood spots were collected at baseline, 1 hour, 2 hours, 4 hours, and 6 hours after drinking the mixture. This revealed an exaggerated increase in plasma phenylalanine levels and persistent elevation of the phenylalanine to tyrosine ratio over the 6 hours above published cutoffs in both pediatric and adult populations at 2 hours, 4 hours, and 6 hours.