Administrative codes combined with medical records based criteria accurately identified bacterial infections among rheumatoid arthritis patients.
OBJECTIVE
To evaluate diagnostic properties of International Classification of Diseases, Version 9 (ICD-9) diagnosis codes and infection criteria to identify bacterial infections among rheumatoid arthritis (RA) patients.


METHODS
We performed a cross-sectional study of RA patients with and without ICD-9 codes for bacterial infections. Sixteen bacterial infection criteria were developed. Diagnostic properties of comprehensive and restrictive sets of ICD-9 codes and the infection criteria were tested against an adjudicated review of medical records.


RESULTS
Records on 162 RA patients with and 50 without purported bacterial infections were reviewed. Positive and negative predictive values of ICD-9 codes ranged from 54%-85% and 84%-100%, respectively. Positive predictive values of the medical records based criteria were 84% and 89% for "definite" and "definite or empirically treated" infections, respectively. Positive predictive value of infection criteria increased by 50% as disease prevalence increased using ICD-9 codes to enhance infection likelihood.


CONCLUSIONS
ICD-9 codes alone may misclassify bacterial infections in hospitalized RA patients. Misclassification varies with the specificity of the codes used and strength of evidence required to confirm infections. Combining ICD-9 codes with infection criteria identified infections with greatest accuracy. Novel infection criteria may limit the requirement to review medical records.
Patkar
Nivedita M
NM
Center for Education and Research on Therapeutics of Musculoskeletal Disorders, University of Alabama at Birmingham, Birmingham, AL 35294-3408, USA.
Curtis
Jeffrey R
JR
Teng
Gim Gee
GG
Allison
Jeroan J
JJ
Saag
Michael
M
Martin
Carolyn
C
Saag
Kenneth G
KG
D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis*; D001424:Bacterial Infections / Q000175:diagnosis*; D003430:Cross-Sectional Studies; D005260:Female; D005568:Forms and Records Control / Q000592:standards; D006801:Humans; D038801:International Classification of Diseases / Q000592:standards*; D008297:Male; D008499:Medical Records / Q000592:standards; D008875:Middle Aged; D012680:Sensitivity and Specificity