Liver and Thyroid Monitoring in Ambulatory Patients Prescribed Amiodarone in 10 HMOs

BACKGROUND: Amiodarone can cause liver and thyroid toxicity, but little is known about compliance with laboratory tests to evaluate liver and thyroid function among ambulatory patients who are dispensed amiodarone. OBJECTIVES: The primary objective of this study was to identify the proportion of ambulatory patients who had liver aminotransferase and thyroid function tests during amiodarone therapy. Secondary objectives were to (1) describe factors associated with receipt of laboratory tests and (2) determine the accuracy of administrative data for assessing aminotransferase and thyroid function monitoring. METHODS: This retrospective cohort study was conducted at 10 health maintenance organizations (HMOs) for the dates of service from January 1, 1999, through June 30, 2001. Participants included 1,055 patients dispensed amiodarone for at least 180 days within this date range; these patients were not necessarily new starts on amiodarone. Administrative claims data were analyzed to assess the percentage of patients with completed alanine/aspartate aminotransferase and thyroid function tests. Depending on the HMO site, electronic or paper medical records were reviewed to evaluate the validity of administrative claims data. Logistic regression models were used to explore factors associated with receipt of laboratory tests. RESULTS: Both aminotransferase and thyroid function tests were completed in 53.3% of patients within a 210-day follow-up period that included the 180-day period of amiodarone dispensings plus 30 days. Thyroid function, with or without liver function (aminotransferase tests), was assessed in 61.9% of patients, and aminotransferase tests, with or without thyroid function, were assessed in 68.2% of patients. After adjusting for patient characteristics and site, the factor most strongly associated with having both types of laboratory tests evaluated was concomitant therapy with a statin (adjusted odds ratio (OR) 1.55; 95% confidence interval (CI), 1.05-2.29). Other factors associated with having both types of laboratory tests evaluated included the number of outpatient visits in the 6 months before the period of amiodarone dispensings (adjusted OR 1.06; 95% CI, 1.00-1.13 for each additional 5 visits) and living in a neighborhood where a higher median percentage of people had a high school or higher education (adjusted OR 1.09; 95% CI, 1.00-1.18 for every 10% increase in educational level at the block level). There was no association between monitoring and patient illness severity as measured by the number of comorbid conditions. On the basis of an evaluation of a randomly selected subset of 104 patient records, the sensitivity and specificity of automated data were 94.2% and 85.7% for aminotransferase tests and 83.3% and 81.1% for thyroid function tests, respectively. CONCLUSIONS: Approximately half of ambulatory patients dispensed amiodarone received both recommended laboratory tests for liver and thyroid function. Improved rates of testing for liver aminotransferase and thyroid function are needed for patients who receive amiodarone.