We agree that severe renal insufficiency is not a contraindication to using an ACE inhibitor or ARB for patients with heart failure. However, some of these patients will have a severe decline in renal function after starting ACE inhibitor or ARB therapy, requiring discontinuation of treatment. Note that if a patient with severe renal insufficiency tolerates ACE inhibitor or ARB treatment, the patient is represented in both the numerator and the denominator. A physician can "get credit" for treating such a patient successfully but does not "fail" the measure if a patient does not tolerate the treatment.

How should performance measures account for comorbid conditions, such as renal insufficiency? Performance measures frequently allow patients who are not receiving guideline-concordant care to be excluded when certain comorbid conditions are present, even if these conditions are not absolute contraindications. Thus, in the case cited above, any patient not prescribed an ACE inhibitor or ARB with certain renal failure diagnosis codes would be excluded from the denominator of the quality measure, although only a subgroup might have sufficient medical justification for withholding treatment. Similarly, patients with heart failure who are not given a ß-blocker would be excluded if asthma or chronic obstructive pulmonary disease were present even though only few patients may have bronchospasm severe enough to outweigh the benefits of treatment. This approach is also problematic because listing a condition as an exclusion may be taken to imply that physicians should not even try to initiate therapy.

Quality measures that rely on these kinds of simplifications are helpful up to a point. When care is only fair, there is room for improvement even among the simple cases. But as care improves, the utility of this kind of measure becomes more limited. To improve quality to very high levels, quality measurement needs to be able to determine whether good care is given to more complex patients. In recognition of the problems of using comorbid conditions as absolute exclusion criteria, the Physician Consortium for Performance Improvement currently recommends using a general "medical reason" exclusion, rather than a comprehensive list of relative contraindications or conditions requiring cautious prescribing. When reporting exclusions, physicians are encouraged to explicitly record in the medical record the reason why a therapy is not given. Electronic health record vendors should create standard methods for physicians to easily record justifications for their clinical decisions to improve the accuracy of quality measurement and minimize time burdens.