Mitigating case mix factors by choice of glycemic control performance measure threshold.
OBJECTIVE
Performance measures are tools for assessing quality of care but may be influenced by patient factors. We investigated how currently endorsed performance measures for glycemic control in diabetes may be influenced by case mix composition. We assessed differences in A1C performance measure threshold attainment by case mix factors for A1C >9% and examined how lowering the threshold to A1C >8% or >7% changed these differences.


METHODS
Using data from the 1999-2002 National Health and Nutrition Examination Survey for 843 adults self-reporting diabetes, we computed the mean difference in A1C threshold attainment of >9, >8, and >7% by various case mix factors. The mean difference is the average percentage point difference in threshold attainment for population groups compared with that for the overall population.


RESULTS
Diabetes medication was the only factor for which the difference in threshold attainment increased at lower thresholds, with mean differences of 5.7 percentage points at A1C >9% (reference), 10.1 percentage points at A1C >8% (P < 0.05), and 14.1 percentage points at A1C >7% (P < 0.001).


CONCLUSIONS
As 87% of U.S. adults have A1C <9%, a performance measure threshold of >9% will not drive major improvements in glycemic control. Lower thresholds do not exacerbate differences in threshold attainment for most factors. Reporting by diabetes medication use may compensate for heterogeneous case mix when a performance measure threshold of A1C >8% or lower is used.
Bainbridge
Kathleen E
KE
Social & Scientific Systems, Silver Spring, Maryland, USA. kbainbridge@s-3.com
Cowie
Catherine C
CC
Rust
Keith F
KF
Fradkin
Judith E
JE
D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000378:metabolism*; D015190:Blood Glucose Self-Monitoring / Q000592:standards* / Q000706:statistics & numerical data; D015992:Body Mass Index; D003920:Diabetes Mellitus / Q000097:blood*; D003940:Diagnostic Techniques, Endocrine / Q000592:standards* / Q000706:statistics & numerical data; D005006:Ethnicity; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D007182:Income; D007348:Insurance, Health / Q000706:statistics & numerical data; D008875:Middle Aged; D044469:Racial Groups
D001786:Blood Glucose; D006442:Glycated Hemoglobin