A mother and her 3-week-old infant arrive at the well-baby clinic for a rescreening test for phenylketonuria (PKU). The nurse reviews the results of the serum phenylalanine levels and notes that the level is 1.0 mg/dl. The nurse interprets this level as?

1. A

   Normal

2. B

   Inconclusive

3. C

   Requiring a repeat study

4. D

   Elevated and indicating PKU

Appeared in: DHS 2018 shift 1st

Explanation

• Phenylketonuria (PKU) is an inborn error of metabolism where the essential amino acid phenylalanine cannot be properly broken down, leading to its accumulation.
• Newborn screening for PKU is a standard public health measure to prevent severe, irreversible intellectual disability through early detection and dietary intervention.
• The normal serum phenylalanine level in a newborn infant is less than 2 mg/dL.
• The infant's reported level of 1.0 mg/dL falls comfortably within this normal range, indicating no evidence of PKU.

Why Other Options Were Wrong

• Option B: A level of 1.0 mg/dL is a definitive normal value and is not ambiguous or borderline.
• Option C: A normal result at 3 weeks of age does not require a repeat study. The infant is past the initial screening window, and this result is reassuring.
• Option D: A level of 1.0 mg/dL is not elevated. Classic PKU is diagnosed with significantly higher levels, typically greater than 20 mg/dL.

Related Visual

Clinical Relevance

• Nursing practice connection: Use the key finding related to Interpretation of newborn screening results for Phenylketonuria (PKU) to guide bedside assessment, documentation, and the next nursing action.
• The nurse's primary role in newborn screening is to ensure the test is performed correctly and at the right time (after 24-48 hours of protein feeding) to ensure accuracy.
• Accurate interpretation of screening results is vital for early intervention. A missed or delayed diagnosis of PKU can lead to devastating and permanent neurological damage.
• Patient education is paramount. If a PKU diagnosis is confirmed, the nurse must educate the family on the strict dietary restrictions (low-phenylalanine diet) necessary to ensure normal development.

How to Approach the Question

• First, identify the key information in the question: the condition being tested for (PKU), the patient's age (3-week-old infant), and the specific lab value (serum phenylalanine 1.0 mg/dL).
• The core task is to interpret this lab value. This requires knowledge of the normal reference range for this test in newborns.
• Recall or look up the normal range for serum phenylalanine in an infant. The normal level is typically < 2 mg/dL.
• Compare the infant's result (1.0 mg/dL) to the normal range. Since 1.0 is less than 2.0, the result is normal.
• Evaluate each option based on this finding. 'Normal' is the only option that aligns with the data. The other options (Inconclusive, Repeat study, Elevated) are incorrect because the result is definitive and within the normal range.

Concept Tested & Keywords

• Concept Tested: Interpretation of newborn screening results for Phenylketonuria (PKU).
• Stem keywords: 3-week-old infant, rescreening test, phenylketonuria (PKU), serum phenylalanine levels, 1.0 mg/dl
• Lead-in keywords: interprets this level as
• Clinical cues: Lab value: 1.0 mg/dl - requires comparison to normal range
• Clinical cues: Condition: Phenylketonuria (PKU) - an inborn error of metabolism

Question ID

QtttMHTjsAXQd0DhFTFXDa

Copy ID

Reference Book

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 856-858