Construct an E1 Eligibility Verification request: Header segment with transaction code E1, BIN and PCN for the target payer; Patient segment with cardholder ID (Field ID 302) or patient name and date of birth if card not available
Include the product/service ID (NDC or drug qualifier) if verifying drug-specific coverage; set Date of Service to today's date
Transmit through the pharmacy switch to the PBM; receive E1 response with eligibility status and coverage details: Group ID confirmation, co-pay tiers, formulary status if returned by the payer, and coordination of benefits order
Parse response Plan fields to identify primary vs. secondary coverage; if the patient has Medicare Part D, confirm BIN/PCN/Group matches the Part D plan sponsor's current formulary year data
Cache eligibility results for the patient visit only (same-day); do not cache across days as benefit eligibility can change (new plan year, loss of coverage, mid-year plan changes)
If E1 returns a rejection indicating no coverage found, attempt secondary payer if available, or prompt staff to collect updated insurance information from the patient
Known gotchas
The E1 transaction returns benefit eligibility, not a guarantee of claim payment; a drug that appears covered in E1 may still reject at B1 claim submission due to formulary restrictions, step therapy requirements, or quantity limits
Not all PBMs support real-time E1 eligibility; some older Medicaid fee-for-service programs use batch eligibility files rather than real-time E1 transactions—check each payer's companion guide
Eligibility responses may not reflect recent enrollment changes (e.g., a patient who just enrolled in Medicare Part D today may not be visible in real-time until the next eligibility file exchange between CMS and the PBM)
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp