Adelaide was born weighing 6-lb, 7 oz and her 1-day newborn screening test result for phenylalanine was 3.7 mg/dl (222 mol/L). She was breastfed with no supplemental formula. A repeat sample was requested to further document the phenylalanine concentration in her blood. The result from this sample, collected on day 4 of life, was 6.2 mg/dl (372 mol/L). To confirm the diagnosis for this child, which was considered to be “presumptive positive,” a quantitative sample was obtained, and phenylalanine and tyrosine levels were both measured. On day of life 9 the serum phenylalanine concentration was 16.6 mg/dl (1328 mol/L), and the tyrosine level was 1.1 mg/dl (60.5 mol/L); the phenylalanine to tyrosine ratio was 22.0:1. Blood and urine were collected for biopterin screening; results were later found to be normal. To provide adequate protein and energy intake and at the same time decrease the serum phenylalanine concentration, a phenylalanine-free formula was introduced at standard dilution without a phenylalanine supplement. Within 24 hours Adelaide’s serum phenylalanine concentration had decreased to 8.3 mg/dl (498 mol/L) while she was being provided an intake of 12 to 14 oz of the Phe-free formula. Breastfeedings were reintroduced; she was offered 3 breastfeedings and Phe-free formula ad lib. Within 48 hours the level was 6.6 mg/dl (396 mol/L), with an intake of 4 oz of the formula. Adelaide’s phenylalanine concentrations were measured every 4 days, and the levels were 3.6 mg/dl (216 mol/L) and 2.2 mg/dl (132 mol/L). In subsequent weeks growth and serum phenylalanine concentrations continued to be monitored carefully, and energy and phenylalanine intakes were adjusted as necessary to maintain blood phenylalanine concentrations between 2 and 6 mg/dl (120 to 360 mol/L) and to maintain growth in appropriate channels. By age 2 months, Adelaide’s intake had increased to approximately 12 oz formula along with three breastfeedings daily (alternating breastmilk and formula feedings), and her feeding pattern was fairly consistent. Blood phenylalanine was measured at 8.7 mg/dl (522 mol/L), which is outside the desired range. Her Phe-free formula was increased to 14 oz/d to effectively decrease the amount of phenylalanine provided by breastmilk.
Nutrition Diagnostic Statement
Altered nutrition-related laboratory values (phenylalanine) related to phenylketonuria and dietary phe intake, as evidenced by blood phenylalanine outside desired range.
Nutrition Care Questions
1. What is the expected energy requirement for Adelaide?
2. What are the baseline expectations for intake for a 6-lb, 7-oz neonate? If breastmilk is expected to provide about half of this amount, how much phenylalanine-free formula would you use to provide protein and energy intakes at recommended levels?
3. What are the growth expectations for Adelaide?
4. What steps would you take if Adelaide’s plasma phenylalanine concentration exceeded 6 mg/dl (360 mol/L) on subsequent measurements?