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Chronic Disease

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Patient factors, not physician or clinic factors, account for most of the variance in blood sugar levels among adults with diabetes

Many adult patients with type 2 diabetes have blood sugar levels above those recommended by evidence-based diabetes care. If more patients achieved the recommended levels, the incidence of heart attacks, strokes, amputations, end-stage renal disease, and blindness may be lowered. Many factors, patient and provider-related, can affect blood sugar levels. However, a new study finds that more than 95 percent of variance in HbA1c values is related to patient factors.

The researchers examined the effects of patient, physician, and clinic factors on HbA1c levels of 2,589 adult patients with diabetes. The HbA1c test measures how well the patient's blood sugar level has been managed over the previous several months. Lower HbA1c levels correlate with lower blood sugar levels. Patients were treated over a 3-year period at 18 clinics (parts of a multispecialty group practice) by 120 primary care physicians. Patient variables included in the study were age, sex, coexisting medical conditions, whether the doctor was a family physician or internist, and medication intensification. Medication intensification was measured by the number of glucose-lowering classes of drugs the patient was prescribed in each year. At the time of the study (1995-1997), there were three classes of drugs for diabetes: insulin, sulfonylurea, and metformin. Physician variables included age, sex, specialty, and number of diabetes patients per physician.

The research team found that more than 95 percent of variance in HbA1c values was attributable to the patient. However, the overall model explained only 11.8 percent of the change in HbA1c values over time. Intensification of medication (a patient factor in which physicians play a major role) was related to favorable change in HbA1c. Neither clinic assignment nor other specific patient and physician factors predicted changes in HbA1c levels.

The study supports the hypothesis that medication intensification may be the final common pathway that leads to better glycemic control. This study was supported by the Agency for Healthcare Research and Quality (HS09946).

See "Variation in quality of diabetes care at the levels of patient, physician, and clinic," by Patrick J. O'Connor, M.D.,M.P.H., William A. Rush, Ph.D., Gestur Davidson, Ph.D., and others in Preventing Chronic Disease 5(1), pp. 1-9, 2008.

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