Administrative OA was defined in two ways based on ICD-9 and ICD-10 codes, referred to as AOA1 and AOA2. AOA1 required at least one visit to a health professional or one hospital admission with the ICD-9 code of 715 or the ICD-10 codes from M15 to M19, and AOA2 required at least two visits to health professionals in two years separated by at least one day or one hospital admission with these codes.
The sensitivity of case definitions AOA1 and AOA2 varied from 47 to 57% and 21 to 26%, respectively.
Of the two administrative definitions, AOA1 had the higher sensitivity and NPV whereas AOA2 had the higher specificity and PPV.
On the basis of likelihood ratios, AOA2 might be useful in ruling in OA.