Interpretation of hemoglobin A(1c) (HbA(1c)) values among diabetic patients: implications for quality specifications for HbA(1c).

BACKGROUND Few studies have examined patients' views, knowledge, and understanding of glycohemoglobin A(1c) (HbA(1c)) testing. We explored such issues in patients with type 1 diabetes and used their statements to estimate analytical quality specifications for HbA(1c) testing. METHODS We recruited 201 patients from a hospital outpatient clinic. A questionnaire was used to collect information on diabetes characteristics, perceived knowledge of HbA(1c), last HbA(1c) value, HbA(1c) target value, and thresholds for action. Patients were asked to indicate the magnitude of change in HbA(1c) from 9.4% that they would consider to be a true (real) change; from their responses, we calculated patient-derived quality specifications for HbA(1c). RESULTS Fifty-eight percent of the patients felt they had "high" knowledge about HbA(1c), and >80% of responders knew their last HbA(1c) value, their target HbA(1c), and the threshold value of HbA(1c) for treatment intensification. The mean acceptable HbA(1c) value was 7.5%. Patients with lower values on their most recent tests reported lower target values for HbA(1c) and lower values for the upper HbA(1c) threshold for treatment intensification. An analytical CV (CV(a)) of 3.1% would be satisfactory for 75% of patients when HbA(1c) is increasing (80% confidence), and a CV(a) of 3.2% would be satisfactory for 75% when HbA(1c) is decreasing (95% confidence). CONCLUSIONS Type 1 patients' perceived knowledge about HbA(1c) testing is high. They are well informed about their own personal results and about target values and the upper HbA(1c) threshold for action. The patient-derived analytical quality specification for imprecision (CV) is 3.1%.