BLQ Rule (blq)

Handles Below Limit of Quantification (BLQ) values in pharmacokinetic data.

Field	Description	Required
before	Value to use before TMAX	✅ Yes
at	Value to use at TMAX	✅ Yes
after	Value to use after TMAX	✅ Yes

Example:

{
    "type": "blq",
    "source_column": "concentration",
    "destination_column": "blq_flag",
    "before": 0,
    "at": 1,
    "after": 2
}

Behavior: Sets BLQ flags based on position relative to TMAX.