Searching for a needle in a haystack: use of ICD-9-CM codes in drug-induced liver injury.
OBJECTIVE
The aim of our study was to compare three search strategies using a computerized administrative database to identify cases of idiosyncratic drug-induced liver injury (DILI) due to amoxicillin/clavulanic acid, phenytoin, valproic acid, and isoniazid.


METHODS
In search 1, electronic medical records from patients seen between 1994 and 2004 with an ICD-9-CM code of acute liver injury were identified and cross-searched for the specific drug names in the dictation text. In search 2, all patients with an ICD-9-CM code of drug poisoning/overdose due to one of the four study drugs were identified. In search 3, patients with a poisoning code as well as an acute liver injury code were identified.


RESULTS
Review of the records from the 7,395 search 1 patients yielded 51 DILI cases (0.7%). In contrast, the 566 search 2 patients yielded only three DILI cases (0.5%). Finally, search 3 provided the greatest specificity but a low rate of detection with only two patients (3.9%) having DILI due to one of the four drugs.


CONCLUSIONS
Acute liver injury ICD-9-CM codes combined with a text search of the dictated medical record yielded the greatest number of DILI cases but was less specific than crossing acute liver injury and poisoning codes. Use of ICD-9-CM codes to identify rare adverse events like DILI remains problematic and highlights the need for prospective surveillance networks.
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor, Michigan, USA.
Kartik
K
Jinjuvadia
Wendy
W
Kwan
Robert J
RJ
Fontana
D000293:Adolescent; D000328:Adult; D000368:Aged; D019980:Amoxicillin-Potassium Clavulanate Combination / Q000009:adverse effects; D056486:Chemical and Drug Induced Liver Injury; D002648:Child; D002675:Child, Preschool; D064420:Drug-Related Side Effects and Adverse Reactions; D005260:Female; D006801:Humans; D007223:Infant; D038801:International Classification of Diseases; D007538:Isoniazid / Q000009:adverse effects; D008107:Liver Diseases / Q000453:epidemiology; D008297:Male; D016347:Medical Records Systems, Computerized; D008824:Michigan / Q000453:epidemiology; D008875:Middle Aged; D010672:Phenytoin / Q000009:adverse effects; D011159:Population Surveillance; D012680:Sensitivity and Specificity; D014481:United States / Q000453:epidemiology; D014635:Valproic Acid / Q000009:adverse effects
D014635:Valproic Acid; D010672:Phenytoin; D019980:Amoxicillin-Potassium Clavulanate Combination; D007538:Isoniazid