Two controls, same side, both past 2 SD

It is 11:02 on a weekday morning. The chemistry analyzer has just finished the second QC run of the shift. The low control reads 104.4 U/L against a target of 100.0 U/L, SD 2.0 U/L. The high control reads 104.6 U/L against the same target and SD. Both values sit beyond +2 SD, and both are on the same side of the mean. The analyzer software has not stopped reporting on its own. Patient results from this run are queued and ready to release.

At 07:00 the same two controls ran clean: 101.0 U/L and 99.0 U/L, both within one SD of target, no flag. Between 07:00 and 11:00 the analyzer processed three patient specimens. Nothing about those patient results looks unusual on its face. The question in front of you is not whether the controls are numerically off, they clearly are, but what to do next: is this a stop-the-line rejection or a routine warning, what kind of error does this pattern suggest, and what happens to the three patient results already released.

The locally defined classic rule set uses 1_2s as a warning, and 1_3s, 2_2s, R_4s, 4_1s, and 10x as rejection rules, with method-neutral control material expressed in arbitrary units. No analyzer, reagent, or patient reference range is implied. The pattern-reading skill and the corrective-action sequence transfer to any quantitative method once your laboratory's actual rule set, run boundaries, and control material are substituted in.

A control value outside its range is a starting observation, not by itself an answer. The rule it triggers, and whether that rule is a warning or a rejection under your local system, determines what you do next.