A nurse is assessing a 3-month-old infant who was recently diagnosed with phenylketonuria (PKU). Which assessment finding would be most characteristic of this condition?
1Excessive weight gain and macrosomia
2Musty or mousy odor to the urine and skin✓ 정답
3Jaundice and hepatomegaly
4Hypoglycemic episodes and lethargy
해설
The musty or mousy odor is the most characteristic early finding in PKU due to accumulation of phenylalanine metabolites. Other options are not typical for PKU; excessive weight gain, jaundice/hepatomegaly, and hypoglycemia are associated with other conditions.
Clinical Judgment
This question assesses the ability to identify the most urgent danger signal in the evaluation of a child with phenylketonuria (PKU). The key is to establish clinical priorities. While all options can be associated with PKU, a musty/mousy odor is a Notify HCP! sign that directly indicates active, ongoing metabolic toxicity and the risk of immediate neurological damage. It signifies that dietary control is insufficient or has not been initiated, requiring immediate intervention to prevent intellectual disability. The other options may be characteristics of PKU or long-term consequences, but this specific odor represents a current biochemical crisis.
Memory Tip: Mousy odor = Metabolic emergency. The "M" smell in PKU means "Must Act Now."
KR vs US: Both Korea and the US diagnose PKU early through newborn screening. The core management principle (low-phenylalanine diet) is the same, but in the US, there may be differences in insurance coverage and access to special formulas and low-protein foods. The nurse's role in education and monitoring is equally important.
Clinical Guide: Phenylketonuria (PKU) Assessment
When assessing an infant with suspected or diagnosed PKU, the nurse must recognize the hallmark clinical sign that may be present before the onset of irreversible neurological damage.
Key Assessment Finding
Musty or Mousy Odor: A distinctive odor to the urine, sweat, and skin is the most characteristic finding. This results from the accumulation and excretion of phenylacetic acid.
Timing: The odor typically becomes noticeable within the first few weeks of life as phenylalanine levels rise, often prompting evaluation if newborn screening was missed.
Nursing Actions
Document the presence and description of any unusual odors immediately.
Monitor for signs of neurological involvement, such as irritability, vomiting, or developmental regression, which can appear by 3-6 months if untreated.
Initiate dietary education for the family regarding a phenylalanine-restricted diet, emphasizing the critical role of medical formula.
Differential Considerations
Galactosemia: Presents with jaundice, hepatomegaly, vomiting, and cataracts after milk feeding begins, not a musty odor.
MCAD Deficiency: Characterized by hypoketotic hypoglycemia, lethargy, and vomiting during periods of fasting or illness.
Maple Syrup Urine Disease (MSUD): Associated with a sweet, maple syrup odor to the urine and cerumen, not a musty odor.
Phenylketonuria (PKU) — An autosomal recessive inborn error of metabolism caused by a deficiency of phenylalanine hydroxylase, leading to accumulation of phenylalanine.
Phenylalanine hydroxylase (PAH) — The liver enzyme that converts the essential amino acid phenylalanine into tyrosine; deficient in PKU.
Phenylacetic acid — A phenylketone produced from the alternative metabolism of excess phenylalanine, responsible for the musty odor in PKU.
Autosomal recessive — A pattern of inheritance where two copies of an abnormal gene must be present for the disease to develop.
Newborn screening — A public health program that tests infants shortly after birth for certain serious genetic, metabolic, or functional disorders, including PKU.