Searching for FHIR Resources

In the previous lesson, we saw how to list all patients from a FHIR server. But that’s just scratching the surface, FHIR’s search functionality lets you filter, sort, and combine queries to find exactly the patients you’re looking for.

Let’s go through some key search techniques using the Patient resource.

Where to Find Search Parameters

Every FHIR resource has its own set of supported search parameters. If you open the Patient resource page in the FHIR specification and scroll down, you’ll find a full list of search parameters.

These parameters allow you to filter patients by attributes such as name, birth date, gender, address, and more.

Basic Search Examples

Search by Name

GET [base]/Patient?name=Sidharth

This returns only patients with the name “Sidharth.”

Search by Birth Date

GET [base]/Patient?birthdate=1997

This gives you all patients born in 1997.

Note: The parameter is birthdate (all lowercase), even though the field in the resource is birthDate with a capital “D”. Search parameters don’t always match the field names exactly.

Using Comparators with Dates

Since birthdate is a date type, you can use comparison operators:

eq → equal to
ne → not equal to
lt → less than
gt → greater than

Example:

GET [base]/Patient?birthdate=lt1997

This returns all patients born before 1997.

Filtering by Gender

GET [base]/Patient?gender=female

This query fetches all female patients on the FHIR server.

Sorting Results

FHIR also allows sorting using the _sort parameter.

Example:

GET [base]/Patient?gender=female&_sort=birthdate

This gives you all female patients, sorted by their birth date. The first result will be the oldest female patient on the server.

You can also sort by metadata fields such as _lastUpdated:

GET [base]/Patient?gender=female&_sort=-_lastUpdated

Adding a minus sign (-) sorts in descending order, so you’ll get the most recently updated patient record first.

Combining Multiple Parameters

You can combine search parameters using &. Example:

GET [base]/Patient?gender=female&name=jane

This fetches all female patients named Jane.

Common Search Parameters

In addition to resource-specific parameters, FHIR defines common parameters available across all resources, such as:

_id → search by resource ID
_lastUpdated → filter by last update timestamp
_tag, _profile, _security → search based on metadata

These parameters provide consistency across different FHIR resources.

This is just the tip of the iceberg. The FHIR search specification is extensive and worth exploring if you want to go deeper.