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A source of error in phenylketonuria screening.

C C Mabry¹, M C Reid, R J Kuhn

¹Department of Pediatrics, University of Kentucky, Lexington 40536.

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.

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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.