Mitigating Case Mix Factors by Choice of Glycemic Control Performance Measure Threshold

  1. Kathleen E. Bainbridge, PHD1,
  2. Catherine C. Cowie, PHD2,
  3. Keith F. Rust, PHD3 and
  4. Judith E. Fradkin, MD2
  1. 1Social & Scientific Systems, Silver Spring, Maryland
  2. 2National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland
  3. 3Westat, Rockville, Maryland
  1. Corresponding author: Kathleen E. Bainbridge, kbainbridge{at}s-3.com

Abstract

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.

RESEARCH DESIGN AND 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.

Footnotes

  • Published ahead of print at http://care.diabetesjournals.org on 28 May 2008.

    Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details.

    The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C Section 1734 solely to indicate this fact.

    • Accepted May 18, 2008.
    • Received October 17, 2007.
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  1. Published online before print May 28, 2008, doi: 10.2337/dc07-2010 Diabetes Care September 2008 vol. 31 no. 9 1754-1760
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