title: Validity of diagnostic codes and laboratory measurements to identify patients with idiopathic acute liver injury in a hospital database.
abstract: OBJECTIVE
  The development and validation of algorithms to identify cases of idiopathic acute liver injury (ALI) are essential to facilitate epidemiologic studies on drug-induced liver injury. The aim of this study is to determine the ability of diagnostic codes and laboratory measurements to identify idiopathic ALI cases.
  
  
  METHODS
  In this cross-sectional validation study, patients were selected from the hospital-based Utrecht Patient Oriented Database between 2008 and 2010. Patients were identified using (I) algorithms based on ICD-9-CM codes indicative of idiopathic ALI combined with sets of liver enzyme values (ALT > 2× upper limit of normal (ULN); AST > 1ULN + AP > 1ULN + bilirubin > 1ULN; ALT > 3ULN; ALT > 3ULN + bilirubin > 2ULN; ALT > 10ULN) and (II) algorithms based on solely liver enzyme values (ALT > 3ULN + bilirubin > 2ULN; ALT > 10ULN). Hospital medical records were reviewed to confirm final diagnosis. The positive predictive value (PPV) of each algorithm was calculated.
  
  
  RESULTS
  A total of 707 cases of ALI were identified. After medical review 194 (27%) patients had confirmed idiopathic ALI. The PPV for (I) algorithms with an ICD-9-CM code as well as abnormal tests ranged from 32% (13/41) to 48% (43/90) with the highest PPV found with ALT > 2ULN. The PPV for (II) algorithms with liver test abnormalities was maximally 26% (150/571).
  
  
  CONCLUSIONS
  The algorithm based on ICD-9-CM codes indicative of ALI combined with abnormal liver-related laboratory tests is the most efficient algorithm for identifying idiopathic ALI cases. However, cases were missed using this algorithm, because not all ALI cases had been assigned the relevant diagnostic codes in daily practice.
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.|Medicines Evaluation Board, Utrecht, The Netherlands.
authors.forename: Renate
authors.initials: R
authors.lastname: Udo
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.
authors.forename: Anke H
authors.initials: AH
authors.lastname: Maitland-van der Zee
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.|Department of Clinical Pharmacy, University Medical Center Utrecht, The Netherlands.
authors.forename: Toine C G
authors.initials: TC
authors.lastname: Egberts
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.|Department of Clinical Pharmacy, University Medical Center Utrecht, The Netherlands.
authors.forename: Johanna H
authors.initials: JH
authors.lastname: den Breeijen
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.|Medicines Evaluation Board, Utrecht, The Netherlands.
authors.forename: Hubert G M
authors.initials: HG
authors.lastname: Leufkens
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.|Department of Clinical Chemistry and Haematology, University Medical Center Utrecht, Utrecht, The Netherlands.
authors.forename: Wouter W
authors.initials: WW
authors.lastname: van Solinge
authors.affiliation: Division of Pharmacoepidemiology and Clinical Pharmacology, Utrecht Institute for Pharmaceutical Sciences, Utrecht University, The Netherlands.|Medicines Evaluation Board, Utrecht, The Netherlands.
authors.forename: Marie L
authors.initials: ML
authors.lastname: De Bruin
mesh_terms: D000465:Algorithms; D056486:Chemical and Drug Induced Liver Injury / Q000175:diagnosis*; D016208:Databases, Factual; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D038801:International Classification of Diseases / Q000592:standards; D008499:Medical Records
keywords: ICD-9-CM codes; acute liver injury; laboratory measurements; pharmacoepidemiology; validity