Comparison of patient questionnaires, medical records, and plasma assays in assessing exposure to benzodiazepines in elderly subjects

Objective: Exposure in pharmacoepidemiologic studies can rely on various so urces such as medical records, patient questionnaires, or plasma samples, w hich do not always concur. This study endeavored to compare sources of info rmation on current exposure to benzodiazepines in elderly subjects. Methods: In a study in a hospital admissions department, 1136 elderly subje cts included in a case-control study each completed a structured questionna ire. In addition, an inspection of the medical records of each subject was performed, as well as screening of a plasma sample thigh-pressure liquid ch romatography-diode array detector) for current exposure to benzodiazepines. Results: Benzodiazepines were found in the plasma of 33% of 1013 patients, in the records of 31% of patients, and in the questionnaires of 36% of 797 respondents. With use of the plasma results as a standard, questionnaires h ad 11% false positives and 28% false negatives; medical records had 14% fal se positives and 23% false negatives. The Ic for concordance between questi onnaires and records was 0.63. Most of the errors were related to the unexp ected presence in plasma of clorazepate, commonly used as a hypnotic agent. Conclusions: Patient recall and medical records are not reliable measures o f current exposure to benzodiazepines in elderly persons, although this unr eliability may be more marked with certain drugs used as hypnotic agents.