We agree that it is difficult to accurately capture disease severity and control with commonly used ICD-9 classifications. For this reason, we used ICD-9-CM codes, along with ambulatory blood pressure measurements, laboratory results, and prescriptions, to identify the presence of hypertension, dyslipidemia, and diabetes mellitus but not to grade their degree of severity or control. As described in our Appendix Table 2 and in our Methods section, we used actual ambulatory blood pressure measurements and laboratory results from the electronic records at Kaiser Permanente to define control and pharmacy records to identify medication intensification. Previous studies have documented the accuracy of the Kaiser Permanente clinical databases used in our study (1, 2). For example, diabetes diagnosis, myocardial infarction, and stroke were all confirmed at chart review in 98%, 99%, and 75% of cases, respectively, as described in our article. Although we cannot exclude some misclassifications in the identification of hypertension, dyslipidemia, and diabetes mellitus, our diagnostic criteria are certainly more accurate than relying on ICD-9 codes alone.

In our study, levels of control were determined by using actual measurements and current clinical guidelines. Because we found that measuring therapy modifications in response to poor control in a large population was feasible, future studies should examine whether giving physicians feedback on this process-of-care measure may increase levels of control. This kind of measurement also has limitations but may provide a more accurate index of the quality of clinical care than relying solely on measures examining the proportion of patients whose condition is under control.