Prognosis supports grouping (combines) in a display, but same feature is not available in thresholds.
For thresholds, it needs summarized data in a record. So if we need to get summary data based on custom groups you mentioned, we can create a custom solution that reads in data from prognosis, summarizes and produces a new record. This new record can then be used in threshold.
Let me know if you want to discuss it further.
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