Ambulatory blood pressure monitoring (ABPM) is a diagnostic test used to measure blood pressure when isolated clinical blood pressure measurements are suspected to be inaccurate. These suspected inaccuracies in blood pressure measurement generally only occur in defined populations. ABPM is conducted under the supervision of a physician and does not entail patient intervention; it is not considered a self-monitoring device. HCFA must evaluate whether current literature supports the clinical use of ABPM and whether or not ABPM is a "reasonable and necessary" for the Medicare population.