Getting Started with VSAC Value Sets

Introduction

VSAC hosts a wide range of value sets created for differing purposes. For example a value set may be created that is intended to define a population such as “homeless”. An other value set relating to homeless might be a set of codes that could be used to determine a probability of homeless (i.e. a patient that has many of the codes in the value set has a higher probability of being homeless). Also, value sets come from a number of different organizations and are created by individuals with differing expertise (e.g. clinical background v. non-clinical contributors).

Therefore, it is critical to evaluate a value set before selecting it for use. Some of the criteria for this evaluation include

The purpose of the value set
The source organization of the value set
The expertises of the creator(s) of the value set
The type of the value set (e.g. Grouping, Extensional, Intensional, etc.)
Before selecting a value set for production use it should be reviewed by both clinicians and informaticists.

There currently is not a repository of VSAC value sets that have been evaluated for fitness for use in the definition of OHDSI phenotypes.

Finding a Value Set (COVID)

In our first example, we will find and evaluate a value set for covid vaccinations.

Search

The VSAC web site provides a search tool that can be used to find candidates for a value set that can be used to define a list of codes that represent covid vaccinations as medication/vaccination codes. To search for this list of value sets go to the VSAC Search Page. Select the “Search Value Sets” tab. Enter “covid vaccination” in the Query text box. Select Search. We can further refine our search results by entering “Active” as the expansion status. Enter CVX as the code system (we know that there should be some CVX codes in the value set we are looking for). Enter “Grouping” as the definition type. VSAC value sets generally include codes from a single code system, Value sets with a definition type of “Grouping” include codes from multiple systems. This should give a list similar to the one shown below. We will be using the “COVID19Vaccine_CVX” value set for this example. Click on the OID for this value set to view the details we will need for the initial assessment of this value set.

View Details

To view the details of the value set select the “Value Set Details” tab in the middle of the page. Select the “Description” tab on the left to see the details for this result set as shown below. Click to see full size.

From the purpose section of this page we can see that this value set might be fit for our purpose of using this value set to define an OHDSI code set for a cohort. However, we also notice that this value set is attributed to a business analyst and we have no indication that this value set was reviewed by a clinician. We next consult the clinician on our team to review this value set. Upon review the clinician indicates that there is a large number of codes that are not included that should be.

Fortunately, our clinician has created a more comprehensive value set. This set will be uploaded to VSAC by our clinician. Once this is done we will be able to use the new value set.

Discussion

VSAC is a powerful resource for the curation and distribution of value sets, both with in OHDSI as well as outside of OHDSI. However, value sets in VSAC serve differing purposes. When selecting a value set from VSAC it is critical to review the value set and to have the value set reviewed by both informatics specialists and clinical experts. The use of VSAC value sets in OHDSI would be greatly enhanced by the creation of a mechanism to identify validated and prefered value sets and associate these value sets with well defined descriptions of how they should be used in an OHDSI context.