Guidance on Mapping Source “Observation” Visits to visit_concept_id in OMOP CDM

Implementers
1

Hello OHDSI Community,

I’m new to OHDSI and the OMOP CDM, and I’m hoping to get some definitive guidance on a foundational mapping question related to visits.

Specifically, I’m looking for documentation and/or community consensus on how a source visit type of “Observation” should be mapped to visit_concept_id in the OMOP visit_occurrence table (v5.4).

The OMOP CDM Visit Occurrence User Guide defines:

  • Inpatient Visit: A person visiting a hospital, at a Care Site, occupying a bed for a duration of more than one day, with physicians and other providers permanently available to deliver services around the clock.
  • Outpatient Visit: A person visiting a dedicated ambulatory healthcare institution, at a Care Site, within one day, without a bed, with physicians or medical providers delivering services during the visit.

From a regulatory and operational perspective (e.g., CMS guidance), Observation stays are generally considered outpatient, even though the patient occupies a bed. Admission to an inpatient unit typically requires a formal admission order by a provider. Observation stays are usually limited to ≤24 hours, though they can occasionally extend to 48 hours.

I’ve searched the OHDSI forums and existing documentation for prior guidance on this topic, but I’ve found conflicting responses and no clear or definitive recommendation. (Very possible I just don’t know where to find it.)

Given how foundational visit mapping is for downstream analyses, I would really appreciate any insights, best practices, or references the community can share. This could include any documented OHDSI guidance or real-world implementation examples addressing this scenario.

Thank you very much for your time and for supporting those of us who are newer to OMOP and OHDSI. I truly appreciate the collective expertise of this community.

Kind regards,
Allison

2

Hello @foya and welcome to OHDSI and the OMOP CDM,

The OMOP CDM is a person centric, country agnostic common data model for health data. So, rules, conventions and guidance on how data are inserted into OMOP is focused on the patient’s experience and journey.

You have found the correct guidance for how to map encounter/visit data to OMOP:

If the encounter is < 24 hours, then it is considered an outpatient visit. The person came, received treatment and went back to their home. If the encounter is > 24 hours, then it is considered an inpatient visit.

Will you and/or your colleagues be joining us at the OHDSI Symposium October 20 - 22nd? If yes, I highly encourage you to join the “Mastering OMOP: Transforming EHR Data with Practical Strategies, Best Practices, and OHDSI Integration” tutorial on the morning of October 20th. This tutorial is taught by a handful of OHDSI and Observational research experts and is specifically designed for those with EHR data.

3

Thank you, @MPhilofsky, for your prompt response.

I have a follow-up question. My apologies if this is obvious—I’m new to OMOP.

To make sure I’m understanding correctly: are you suggesting that we implement logic in our ETL similar to the following when assigning visit_concept_id?

If visit_source_value = Observation AND LOS ≤ 24h → Outpatient (9202)
Else If visit_source_value = Observation AND LOS > 24h → Inpatient (9201)

Is that an appropriate interpretation of your guidance, or are there additional considerations we should account for when mapping observation visits?

Thanks again!

4

Yes, exactly this:

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