Timeliness of clinical laboratory services is customarily evaluated by monitoring test turnaround time (TAT). TAT is usually defined as the period of time between test order receipt and test reporting. However, this definition underestimates TAT, since non-analytical activities may have a much larger impact on timeliness than laboratory analytical activities. For example, in the emergency depatrment, delay in review of results by clinicians can greatly impact timeliness of patient treatment. Therefore, a more useful definition of TAT is the interval between when a test is ordered and the time a treatment decision is made.