Abstract Background Our hospital system recently reorganized its lab services so as to restrict in-house testing almost exclusively to inpatient testing. This disruption in patient mix caused us to reassess properties of running averages for our most common analytes, for potential use of such data in real-time patient-based quality control (PBQC). In particular, we examined whether there were analytes for which there was significant dependence of running averages on 24-h clock time (time-of-day, TOD). Methods We performed a retrospective analysis of 3-months' data (FY24, Q2) for patient results of 13 components of the Basic Metabolic Panel (BMP) and Comprehensive Metabolic Panel: Albumin*, Alkaline phosphatase, Alanine amino transferase, Aspartate aminotransferase*, Calcium*, Chloride*, CO2*, Creatinine, Potassium*, Total Protein*, Sodium, Total Bilirubin, and Urea. Running averages for 20 consecutive results (20-mers) were computed for data restricted to results within reference intervals. This produced an overall mean (X) and standard-deviation (SD) of 20-mers for each analyte. We then computed the average 20-mer result (Y) reported within 1-h bins across 24-hour clock time (t). Y(t) was regarded as having TOD-dependence if: (a) there was an 8-h interval of contiguous results for Y that were strictly either below or above X; and (b) either nadir or apex values for |Y-X| exceeded 0.5 SD. Results Seven analytes (*, above) demonstrated TOD-dependence of running means for 20-mers according to criteria given above. An example of TOD-dependent Y(t) is shown in Figure (Albumin). Conclusions For our hospital, TOD-dependence of running means was identified for 7 of 13 metabolic panel analytes. TOD-dependence of running means is a circumstance in which use of only a fixed target for running means in PBQC would lead to inherent TOD-dependent variation in capability for systematic error detection. Use of TOD-dependent targets for PBQC would be appropriate in these cases.