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A source of error in phenylketonuria screening.
American Journal of Clinical Pathology
|September 1, 1988
Summary
Newborn screening for phenylketonuria (PKU) can be complicated by ampicillin interference. Autoclaving blood specimens with ampicillin causes falsely high phenylalanine levels, risking misdiagnosis.
Area of Science:
- Clinical Chemistry
- Neonatal Screening
- Medical Diagnostics
Background:
- Newborn screening for phenylketonuria (PKU) is crucial for early diagnosis and treatment.
- Traditional Guthrie bacteriologic inhibition assay (BIA) results can be uninterpretable in infants receiving antibiotics.
- The McCaman-Robins chemical-fluorescent assay (CFA) is used to re-evaluate ambiguous BIA results.
Observation:
- Spurious elevations in blood phenylalanine levels were observed in four infants receiving ampicillin.
- These elevated levels occurred when blood specimens collected on filter paper were autoclaved prior to analysis.
- The interference was linked to ampicillin and the heat from the autoclaving process.
Findings:
- Ampicillin causes fluorescent interference when specimens are autoclaved, leading to falsely high phenylalanine readings.
- This interference mimics high phenylalanine levels, potentially leading to misdiagnosis of PKU.
- None of the affected infants actually had PKU.
Implications:
- Autoclaving blood specimens prior to analysis can compromise diagnostic accuracy for PKU.
- Healthcare providers should avoid autoclaving blood specimens intended for BIA or CFA analysis.
- This finding is critical for accurate neonatal screening and timely PKU diagnosis.
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