Medical Decision Limits are described as a "second set of limits set for control values ...meant to be a wider set of limits indicating the range of medically acceptable results." The idea is that these medical decision limits embody the medical usefulness requirement for a test and by drawing these limits on our control charts, we will detect medically significant errors. Using CLIA QC requirements and practical examples, Dr. Westgard evaluates these MDLs and reveals their true nature.