The National Institute for Health and Clinical Excellence group divided known Track and Trigger systems into four categories
| Single parameter system | Periodic observation of selected vital signs that are compared with a simple set of criteria with predefined thresholds, with a response algorithm being activated when any criterion is met. |
| Multiple parameter system | Response algorithm requires more than one criterion to be met, or differs according to the number of criteria met. |
| Aggregate scoring system | Weighted scores are assigned to physiological values and compared with predefined trigger thresholds. |
| Combination system | Single or multiple parameter systems used in combination with aggregate weighted scoring systems. |
Source: NICE. Acutely ill patients in hospital: Recognition and response to acute illness in adults in hospitals.4