Cut your QC Question: a 1-2s by the light of the moon

We got a lot of questions during our Cut Your QC webinar, too many to answer during the session. So here's one that we didn't get to

"In the evening I run one level of QC and it fails 1:2s. Do I need to rerun?"

This is a curious question. QC results are not different depending on the time of day. A 1:2s in the morning is the same as a 1:2s at night. Quite likely the staffing situation is different at those times of day, and the energy level of a night shift running QC is possibly lower than a day shift.

But ask yourself, if I encountered a rule violation, would it matter at what point in the earth's rotation you were currently in? Does a 1:2s look worse in the dark of night, but sunnier in the light of day? 

You will not find CLIA regulations, CAP checklists, or ISO 15189 recommendations that vary based on the time of day.
A rule violation is a rule violation, no matter the sun or moon, no matter the clouds or fog, for that matter.

In this particular situation, however, the specific rule discussed is worth noting. The 1:2s is notoriously error-prone, generating 9 to 14% false rejections depending on the number of control levels being run. Rather than focus on the time of day, it's more productive to determine which control rules are actually necessary. Through analytical Sigma metrics and Westgard Sigma Rules, you can get optimized QC rules, and those will not include a 1:2s rule, not for rejection and not even for warning. So possibly, the answer to this question will be, you won't even be worrying about 1:2s, no matter the time of day.