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​False-positive paracetamol levels in a patient with hyperbilirubinaemia: clinical perspectives.
BMJ Case Rep. 2020 Jun 30; 13(6)BC

Abstract

​Serum concentrations of paracetamol are measured to investigate the cause of acute hepatitis, monitor the clearance of paracetamol from the body and to determine if supratherapeutic levels warrant treatment with N-acetylcysteine (NAC). ​A 49-year-old man treated for ischaemic colitis developed worsening renal and liver function tests. As part of the investigation of hepatorenal failure, paracetamol levels were requested, which were elevated at 14 mg/L (normal <4 mg/L) resulting in treatment with NAC. Despite treatment, levels of paracetamol remained elevated and the link between hyperbilirubinemia and false-positive paracetamol levels was identified. ​Bilirubin and its by-products have intense absorbance in the ultraviolet and visible regions of the electromagnetic spectrum, causing interference in the enzymatic colorimetric assay most commonly used to measure paracetamol concentration, resulting in false-positive paracetamol levels. Laboratories correct for this interference above a predetermined bilirubin concentration, termed the Icteric Index; however, in our case this interference occurred at a lower level of hyperbilirubinaemia than previously identified as significant. This interaction was found to be more significant at lower bilirubin levels when low or no paracetamol levels were present in the serum, resulting in a change to laboratory practice and development of a 'Sliding Scale' approach to analysis. ​Concurrent bilirubin or Icteric Index measurement is recommended for all laboratories that use the enzymatic colorimetric assay for paracetamol measurement. Lower Icteric Index or bilirubin thresholds are required when low or no paracetamol levels are present in the serum to prevent false-positive paracetamol results. We describe a new 'Sliding Scale' approach to analysis, and highlight an important interaction for clinicians to be aware of.

Authors+Show Affiliations

Royal Preston Hospital, Preston, UK j.james3@doctors.org.uk.Royal Preston Hospital, Preston, UK.Royal Preston Hospital, Preston, UK.Royal Preston Hospital, Preston, UK.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

32606118

Citation

James, Joel, et al. "​False-positive Paracetamol Levels in a Patient With Hyperbilirubinaemia: Clinical Perspectives." BMJ Case Reports, vol. 13, no. 6, 2020.
James J, Stauss M, Ponnusamy A, et al. ​False-positive paracetamol levels in a patient with hyperbilirubinaemia: clinical perspectives. BMJ Case Rep. 2020;13(6).
James, J., Stauss, M., Ponnusamy, A., & Myers, M. (2020). ​False-positive paracetamol levels in a patient with hyperbilirubinaemia: clinical perspectives. BMJ Case Reports, 13(6). https://doi.org/10.1136/bcr-2020-234702
James J, et al. ​False-positive Paracetamol Levels in a Patient With Hyperbilirubinaemia: Clinical Perspectives. BMJ Case Rep. 2020 Jun 30;13(6) PubMed PMID: 32606118.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - ​False-positive paracetamol levels in a patient with hyperbilirubinaemia: clinical perspectives. AU - James,Joel, AU - Stauss,Madelena, AU - Ponnusamy,Arvind, AU - Myers,Martin, Y1 - 2020/06/30/ PY - 2020/7/2/entrez KW - drugs: gastrointestinal system KW - hepatitis other KW - nonalcoholic steatosis JF - BMJ case reports JO - BMJ Case Rep VL - 13 IS - 6 N2 - ​Serum concentrations of paracetamol are measured to investigate the cause of acute hepatitis, monitor the clearance of paracetamol from the body and to determine if supratherapeutic levels warrant treatment with N-acetylcysteine (NAC). ​A 49-year-old man treated for ischaemic colitis developed worsening renal and liver function tests. As part of the investigation of hepatorenal failure, paracetamol levels were requested, which were elevated at 14 mg/L (normal <4 mg/L) resulting in treatment with NAC. Despite treatment, levels of paracetamol remained elevated and the link between hyperbilirubinemia and false-positive paracetamol levels was identified. ​Bilirubin and its by-products have intense absorbance in the ultraviolet and visible regions of the electromagnetic spectrum, causing interference in the enzymatic colorimetric assay most commonly used to measure paracetamol concentration, resulting in false-positive paracetamol levels. Laboratories correct for this interference above a predetermined bilirubin concentration, termed the Icteric Index; however, in our case this interference occurred at a lower level of hyperbilirubinaemia than previously identified as significant. This interaction was found to be more significant at lower bilirubin levels when low or no paracetamol levels were present in the serum, resulting in a change to laboratory practice and development of a 'Sliding Scale' approach to analysis. ​Concurrent bilirubin or Icteric Index measurement is recommended for all laboratories that use the enzymatic colorimetric assay for paracetamol measurement. Lower Icteric Index or bilirubin thresholds are required when low or no paracetamol levels are present in the serum to prevent false-positive paracetamol results. We describe a new 'Sliding Scale' approach to analysis, and highlight an important interaction for clinicians to be aware of. SN - 1757-790X UR - https://www.unboundmedicine.com/medline/citation/32606118/​False-positive_paracetamol_levels_in_a_patient_with_hyperbilirubinaemia:_clinical_perspectives L2 - https://casereports.bmj.com/cgi/pmidlookup?view=long&amp;pmid=32606118 DB - PRIME DP - Unbound Medicine ER -
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