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False positive acetaminophen concentrations in icteric serum
L de Jong1, D G Knapen2, T H Oude Munnink3
1Department of Clinical Pharmacy, Hospitalgroup Twente, Almelo, The Netherlands.
Practical Laboratory Medicine
|September 1, 2017
Summary
Elevated bilirubin in icteric serum can cause falsely high acetaminophen levels when using enzymatic assays. Confirm questionable results with non-enzymatic methods to ensure accurate diagnosis and treatment.
Area of Science:
- Clinical Chemistry
- Toxicology
- Analytical Chemistry
Background:
- Acetaminophen levels are crucial for managing overdose and identifying unknown liver injury.
- N-acetyl cysteine is the antidote for acetaminophen poisoning, and its administration is guided by serum acetaminophen concentrations.
Observation:
- A patient with hepatic encephalopathy and high bilirubin presented with persistently elevated acetaminophen levels (11.5-12.3 mg/l) over 4 days using an enzymatic-colorimetric assay.
- High-performance liquid chromatography (HPLC), a non-enzymatic method, showed undetectable acetaminophen levels in the same patient.
Findings:
- Elevated bilirubin in icteric serum interfered with the enzymatic-colorimetric assay, leading to false-positive acetaminophen results.
- Bilirubin's absorbance properties in the UV-visible spectrum likely caused the assay interference.
Implications:
- Enzymatic-colorimetric assays for acetaminophen may yield inaccurate results in patients with jaundice.
- Questionable acetaminophen results in icteric serum necessitate confirmation using non-enzymatic methods, ultrafiltration, or dilution studies.
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