Custom healthcare platforms often ship billing as a finance integration — Xero, Sage, middleware — while clinical modules keep their own patient rows. The architecture tax arrives later: ASTM results validated on the bench never become ChargeItems; HL7 FT1 segments pile up in a queue; FHIR Claim facades pretend interoperability while engineers run nightly SQL to match invoices to encounters.
Design billing as encounter projections
Revenue in practice software is a read model over clinical facts — procedures completed, consumables applied, lab panels validated. Persist charges as encounter-scoped events, then materialize Invoice documents for patients and Claim payloads for payers. The FHIR Invoice resource models hospital-side bills from ChargeItems; Claim models insurer adjudication — keep those bounded contexts explicit in your domain layer.
ASTM and HL7 at the adapter boundary
Prolab-style adapters should translate ASTM E1394 and HL7 v2 ORU into validated result events — keyed by order, accession and patient UUID. Billing handlers subscribe with idempotent consumers; duplicate instrument transmissions must not duplicate charges.
HL7 FT1 segments in DFT messages map cleanly to internal ChargeItem events when visit identifiers resolve. If they do not resolve, dead-letter — never write orphan lines finance will dispute.
Tariff maps as versioned configuration
ChargeItemDefinition patterns from the Order Catalog IG are the right mental model: clinical orderables separate from billing codes and price components with effective dating. Hard-coding insurer rates in adapter code guarantees emergency deploys when Bupa updates a pack.
Promed HIS keeps clinical and billing on one tenant — platform evaluation: medical office accounting software; custom healthcare delivery: practice management software.
Platform review prompts
- Single patient UUID per tenant — billing events forbidden from minting parallel IDs?
- Encounter aggregate replays charges without cross-service joins?
- FHIR APIs expose Invoice/Claim — clinical writes still route through encounter services?
- ASTM/HL7 contract tests in CI with production-like fixtures?
- Finance exports include encounter UUID for accountant traceability?
Ask Competitor B whether middleware owns Patient merge — if yes, clinical safety and revenue integrity both depend on a bus you do not control.
Delete these patterns in sprint zero
Finance microservice with writable Patient table. Cron that bills “unmatched results” without encounter context. ClaimResponse handlers patching clinical encounters. Spreadsheet tariff imports in production config.
Medical office accounting on custom platforms is integration architecture done honestly — FHIR and ASTM at the edges, encounter spine in the middle, ledgers at the perimeter.
