ASCP DLM Practice Exam 2026 – Complete Prep Resource

The 1-3s rule specifies that a run is considered out of control when one result exceeds +/- 3 standard deviations (SD). This rule is a critical component of quality control in laboratory settings, establishing a clear threshold for determining when a control run may produce erroneous results. By focusing on the extremes represented by +/- 3 SD, the 1-3s rule aids in identifying when a process is significantly deviating from expected performance, thereby indicating potential issues that need investigation.

Utilizing this rule helps ensure the reliability of laboratory testing by prompting a review of procedures and equipment when an out-of-control situation is detected. In contrast, the other options do not align accurately with the definition of the 1-3s rule; for instance, accepting a run when both controls are within 2 SD or rejecting a run exceeding +/- 2 SD does not specifically address the out-of-control definition that the 1-3s rule encapsulates. Therefore, recognizing that an out-of-control condition is triggered by results falling outside the +/- 3 SD range is pivotal for maintaining accurate quality control in laboratory operations.