Do clinical practice guidelines improve processes or outcomes in primary care?

BACKGROUND: Clinical practice guidelines (CPGs) are common, but it is not clear whether they improve care. METHODS: Quality indicators for processes and outcomes of care were obtained from a computerized system-wide database by patient administration and utilization management personnel unaware of this study and without connection to or interests in guideline implementation. These indicators were compared before and after guideline implementation. RESULTS: After the asthma CPG, nebulizer treatments, emergency department visits, and admissions decreased significantly (p < 0.001 for all three) and education increased significantly (p < 0.001). Periodic measurements of lung function and controller medication prescriptions were unchanged. After the diabetes mellitus CPG, microalbumin screens and education increased significantly (p < 0.001). Angiotensin-converting enzyme inhibitor prescriptions and yearly foot examinations decreased significantly, along with the percentage of patients with blood pressure of < or = 130/85 mm Hg (p < 0.001). Mean hemoglobin A(1C) levels did not change significantly. After the tobacco cessation CPG, screening and education increased significantly (p < 0.001 and p = 0.04, respectively). CONCLUSIONS: The asthma CPG improved some processes and all outcomes. The diabetes CPG improved two of the eight measured processes but had no effect on outcomes. Education and screening, but not counseling, improved with the tobacco CPG. CPGs appear to improve diagnostic and educational processes more than provider-dependent treatment processes. Outcomes were improved after implementation of the asthma CPG but not after the diabetes CPG.