This is a recorded version of the AACC webinar "Delta Checks in Action: An Essential Quality Improvement Tool" which was originally held March 21, 2012. Delta checks play a pivotal role in the quality improvement process by comparing current laboratory results to previous results. If there is a discrepancy between the results it could be due to either sample error, analytical error or a change in the patient's condition. Many pre-analytical issues cannot be detected by traditional QC methods, which could lead to the reporting of erroneous results. And without the delta check a significant change in a patient's result would not be flagged. Our expert explains methods to customize delta check limits for your laboratory, how to identify sources of pre-analytical, analytical and biological variation and how they may affect laboratory results, methods to investigate discrepant laboratory results and the clinical implications of reporting discrepant results.