Validation of an International Classification of Diseases, Ninth Revision Code Algorithm for Identifying Chiari Malformation Type 1 Surgery in Adults.
BACKGROUND
The use of administrative billing data may enable large-scale assessments of treatment outcomes for Chiari Malformation type I (CM-1). However, to utilize such data sets, validated International Classification of Diseases, Ninth Revision (ICD-9-CM) code algorithms for identifying CM-1 surgery are needed.


OBJECTIVE
To validate 2 ICD-9-CM code algorithms identifying patients undergoing CM-1 decompression surgery.


METHODS
We retrospectively analyzed the validity of 2 ICD-9-CM code algorithms for identifying adult CM-1 decompression surgery performed at 2 academic medical centers between 2001 and 2013. Algorithm 1 included any discharge diagnosis code of 348.4 (CM-1), as well as a procedure code of 01.24 (cranial decompression) or 03.09 (spinal decompression, or laminectomy). Algorithm 2 restricted this group to patients with a primary diagnosis of 348.4. The positive predictive value (PPV) and sensitivity of each algorithm were calculated.


RESULTS
Among 340 first-time admissions identified by Algorithm 1, the overall PPV for CM-1 decompression was 65%. Among the 214 admissions identified by Algorithm 2, the overall PPV was 99.5%. The PPV for Algorithm 1 was lower in the Vanderbilt (59%) cohort, males (40%), and patients treated between 2009 and 2013 (57%), whereas the PPV of Algorithm 2 remained high (≥99%) across subgroups. The sensitivity of Algorithms 1 (86%) and 2 (83%) were above 75% in all subgroups.


CONCLUSIONS
ICD-9-CM code Algorithm 2 has excellent PPV and good sensitivity to identify adult CM-1 decompression surgery. These results lay the foundation for studying CM-1 treatment outcomes by using large administrative databases.
Departments of *Neurological Surgery and #Otolaryngology and Divisions of ‖Biostatistics, §Infectious Diseases, and ¶Public Health Sciences, Washington University School of Medicine in St. Louis, St. Louis, Missouri; ‡Department of Neurological Surgery, Vanderbilt University Medical Center, Nashville, Tennessee.
Jacob K
JK
Greenberg
Travis R
TR
Ladner
Margaret A
MA
Olsen
Chevis N
CN
Shannon
Jingxia
J
Liu
Chester K
CK
Yarbrough
Jay F
JF
Piccirillo
John C
JC
Wellons
Matthew D
MD
Smyth
Tae Sung
TS
Park
David D
DD
Limbrick
D000328:Adult; D000465:Algorithms; D001139:Arnold-Chiari Malformation / Q000145:classification / Q000175:diagnosis* / Q000601:surgery*; D015331:Cohort Studies; D019299:Decompression, Surgical; D004621:Embolization, Therapeutic; D005188:False Negative Reactions; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D038801:International Classification of Diseases; D007796:Laminectomy; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012737:Sex Factors