BioSense Platform Creates an Identifier Unique to Each Visit


Learn more about how the BioSense Platform collapses all data associated with a patient’s visit into a single record by creating a unique patient visit identifier.

Patient in hospital bed, with doctor charting at the bedside

How it's done

The BioSense Platform identifies a unique patient visit by using a calculated field called C_BioSense_ID. This ID is a concatenation of three other calculated fields:

  • C_Visit_Date
  • C_Biosense_Facility_ID
  • C_Unique_Patient_ID

Each field is calculated in a way that ensures it will never be null. Consequently, the visit identifier is always unique to a visit, provided the underlying data are populated as expected based on the current standard, PHIN Messaging Guide for Syndromic Surveillance 2.0. The C_BioSense_ID is the key field used to collapse all messages received for a visit into a single record in ESSENCE.

C_Visit_Date is derived from the calculated field C_Visit_Date_Time, which is populated using the first non-null value from:

  1. Admit Date/Time (PV1-44.1) (PREFERRED)
  2. Earliest Date/Time from:
    1. Discharge Date/Time (PV1-45.1)
    2. Procedure Date/Time (PR1-5.1)
    3. Patient Death Date/Time (PID-29.1)
    4. Recorded Date/Time of Message (EVN-2.1)
    5. Date/Time of Message (MSH-7.1)

Admit_Date_Time is the preferred value, as all others can cause a single visit to appear to have occurred on several dates. Per the current standard, this field is expected to remain unchanged during a patient visit except upon admission to inpatient.

The C_Biosense_Facility_ID field uniquely identifies the facility across the BioSense Platform and in ESSENCE, regardless of identifiers received in messages. During data processing, the BioSense Platform uses the Operational Crosswalk table to ensure that the treating and sending facility IDs are valid for processing and to assign C_BioSense_Facility_ID and other calculated field values as specified by BioSense Platform data processing rules. Refer to the BioSense Platform Quick Start Guide to Using the Master Facility Table for more information on the Operational Crosswalk.

C_Unique_Patient_ID is calculated by scanning the following fields/HL7® segments in this order. It uses the Medical Record number, or if it is not provided, the first non-null value.

  1. Medical_Record_Number (PID-3)
  2. Patient ID (PID-2.1) [Legacy]
  3. First_Patient_ID (PID-3)
  4. Visit_Number (PV1-19)
  5. Patient_Account_Number (PID-18)

Discussions with NSSP Community of Practice subject experts concluded the best practice would be to rely on Medical Record Number and fall back on other segments. Per the current standard, PID-3 and PID-19 are required to be populated in every message and should not be updated during a patient visit. The current standard recommends that the Medical Record Number be provided in PID-3.

Each of these three fields is instrumental in creating the unique visit identifier for ESSENCE ingestion, as the patient identifier may not be unique across facilities. The preferred patient identifier, Medical_Record_Number, may even be reused within data from a single facility.

Reach out with questions‎

If you have questions about how patient visits are collapsed into a single record in ESSENCE or how the C_BioSense_ID field is populated, please contact the NSSP Onboarding Team by creating an NSSP Service Desk ticket or emailing

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