title: Ranitidine interference with standard amphetamine immunoassay.
abstract: BACKGROUND
  We recently encountered several cases of possible false positive results of amphetamine on the Beckman Coulter AMPH assay, but not on the Siemens EMIT II Plus assay. Our clinical chart review suggested that ranitidine interference may be responsible for the false positive results of the AMPH assays.
  
  
  METHODS
  Blank urine specimens spiked with ranitidine concentrations ranging from 5μg/ml to 5mg/ml were analyzed on both the AMPH and EMIT II Plus assays. To examine if the false positive results were due to assay specific reagent/sample ratios, we prepared 3 different sample to reagent ratios and analyzed them for amphetamine reaction rates on both assays.
  
  
  RESULTS
  Ranitidine at 160μg/ml caused a positive interference on the AMPH assay. No interference was observed by ranitidine on the EMIT II Plus assay. Specifically, the sample to reagent ratios tested neither eliminated the positive inference on the AMP assay nor introduced an interference on the EMIT II Plus assay.
  
  
  CONCLUSIONS
  Unlike the EMIT II Plus assay, the AMPH assay has cross-activity with ranitidine, which is independent of sample to reagent ratio.
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States.
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Wheeler
authors.affiliation: Clinical Laboratories, University of Pittsburgh Medical Center Presbyterian and Shadyside Hospitals, Pittsburgh, PA, United States.
authors.forename: Jacqueline A
authors.initials: JA
authors.lastname: Rymer
authors.affiliation: Clinical Laboratories, University of Pittsburgh Medical Center Presbyterian and Shadyside Hospitals, Pittsburgh, PA, United States.
authors.forename: Darla
authors.initials: D
authors.lastname: Lower
authors.affiliation: Clinical Laboratory, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA, United States.
authors.forename: Jayne
authors.initials: J
authors.lastname: Zona
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States; Clinical Laboratories, University of Pittsburgh Medical Center Presbyterian and Shadyside Hospitals, Pittsburgh, PA, United States; Clinical Laboratory, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA, United States.
authors.forename: Octavia M
authors.initials: OM
authors.lastname: Peck Palmer
authors.affiliation: Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States; Clinical Laboratories, University of Pittsburgh Medical Center Presbyterian and Shadyside Hospitals, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States; Clinical Laboratory, Children's Hospital of Pittsburgh of UPMC, Pittsburgh, PA, United States. Electronic address: tamamakj@upmc.edu.
authors.forename: Kenichi
authors.initials: K
authors.lastname: Tamama
mesh_terms: D000661:Amphetamine / Q000652:urine*; D000911:Antibodies, Monoclonal / Q000737:chemistry; D000697:Central Nervous System Stimulants / Q000652:urine*; D003429:Cross Reactions; D004347:Drug Interactions; D005189:False Positive Reactions; D008401:Gas Chromatography-Mass Spectrometry; D006635:Histamine H2 Antagonists / Q000652:urine*; D006801:Humans; D007118:Immunoassay / Q000295:instrumentation*; D011899:Ranitidine / Q000652:urine*; D011933:Reagent Kits, Diagnostic / Q000592:standards; D015813:Substance Abuse Detection / Q000592:standards*
chemical_list: D000911:Antibodies, Monoclonal; D000697:Central Nervous System Stimulants; D006635:Histamine H2 Antagonists; D011933:Reagent Kits, Diagnostic; D011899:Ranitidine; D000661:Amphetamine