Purpose To validate two established questionnaires [Morisky and Medication Adherence Report Scale (MARS-5)] for the measurement of medical adherence of patients treated with antihypertensive drugs in primary care in Germany.
Setting General practitioners (GPs) and their patients in North Rhine-Westphalia, Germany.
Methods GPs were asked to recruit 12 consecutive patients using blood-pressure-lowering medication for at least 12 months. Patients were asked to fill out both the Morisky and MARS-5 questionnaires. The medication possession ratio (MPR) was calculated as reference standard for patients' medication adherence by using GPs' electronic patient records. The results of the questionnaires were then compared with the reference standard.
Results A total of 14 GPs recruited 163 patients of which 128 were included in the analysis. Of the 128 patients, 52% were females; the age ranged from 44 to 96 years (mean 71). The overall adherence rate measured by the MPR was 62.1%. Compared to the reference standard, the Morisky Scale had a sensitivity of 31.9%, a specificity of 72.8% and a positive likelihood ratio (+LR) of 1.18. The MARS-5 had a sensitivity of 8.5%, a specificity of 97.4% and a +LR of 3.28.
Conclusion The Morisky Scale and the MARS-5 cannot be recommended for measuring the adherence to antihypertensive drugs in a general practice setting in Germany at this point. These results emphasize the necessity to validate questionnaires in a specific setting before using them as instruments within a trial different from the original setting(s) of validation.