US health systems running on the major EHRs in 2026 still have a lot of legacy form infrastructure. Some are HL7 v2 message-driven, some are PDF-with-overlay, some are vendor-specific scripting languages built into the EHR. The question of whether to move that infrastructure to FHIR Questionnaire is no longer an academic one; CMS and ONC pressure on interoperability has made it a procurement-cycle question. The honest comparison is that FHIR Questionnaire wins on most criteria, but the migration is not free.
Here is the head-to-head, with attention to what the migration actually costs and where the legacy engines still hold ground. The complete guide to SDC form builders for US healthcare in 2026 is a useful primer, and more on healthcare data exchange in the USA holds the broader context.
What the Legacy Engines Still Do Well
The legacy form engines built into the dominant US EHRs have one major advantage: they are already deployed and the clinical workforce is trained on them. A form built in the EHR vendor's scripting language has zero integration friction because the EHR runs it natively. The screens hang off the same login, the data lands in the same database, and the support pathway flows to the EHR vendor's help desk.
For US health systems with deep investment in a single EHR vendor, this incumbency is not nothing. The cost of disturbing the existing form workflow has to be weighed against the benefits of switching.
Where FHIR Questionnaire Beats the Legacy Approach
FHIR Questionnaire wins on portability, vendor neutrality, and structured data extraction. A Questionnaire authored once renders the same in the EHR portal, a stand-alone patient app, and a vendor-neutral kiosk. The QuestionnaireResponse can be extracted into Observations, Conditions, or Procedures using SDC-defined extraction rules, which means the data shows up in the clinical data warehouse with the right semantics rather than as a free-text blob.
The CMS Interoperability rule and the Da Vinci implementation guides assume FHIR resources flow through the system. Legacy form engines do not natively produce those resources; they require a downstream conversion step that is brittle and lossy.
The Migration Cost That Is Real
Migrating from a legacy form engine to FHIR Questionnaire is not free. Every form in the legacy library has to be re-authored, every calculatedExpression has to be re-implemented, every site-specific tweak has to be documented and ported. The clinical training cost is non-trivial because the new form looks different to the nurse at the front desk.
For a US health system with hundreds of legacy forms, the migration is a multi-quarter program, not a sprint. Many systems start with a single high-value form - the intake screening, the social-determinants assessment, the consent form - and expand from there. The piecemeal approach lets the system learn what works before committing to the full library.
Hybrid Patterns That Work
Several US health systems run a hybrid pattern: the high-value patient-facing forms move to FHIR Questionnaire, while the deeply EHR-integrated provider-facing workflows stay on the legacy engine. The FHIR forms feed the patient portal and the population-health analytics; the legacy forms keep the bedside experience intact. The hybrid avoids the all-or-nothing migration trap.
This pattern works because the two systems do not have to share the same authoring layer. The QuestionnaireResponse data lands in the same warehouse via different pipes.
When to Move and When to Wait
A US health system facing a CMS reporting deadline that depends on USCDI-aligned data should move the affected forms to FHIR Questionnaire promptly. A system without that pressure can stage the migration around natural EHR upgrade cycles. The Top 7 FHIR form builders for US EHR development in 2026 covers the tools that make the migration tractable; the harder work is the operational planning around the change. The honest stance for 2026 is that FHIR Questionnaire is where the puck is going, and the migration is worth starting even if completing it will take years.
Sources
- Questionnaire resource canonical - HTML spec, HL7 FHIR R5, evergreen
- SDC Implementation Guide intro - HTML spec, HL7, evergreen
- Interoperability and Patient Access fact sheet - HTML fact sheet, CMS, 2020
