HL7 v2 Reference

What Is HL7 v2 GT1-6? Guarantor Phone Number - Home, Explained for Testers

Jul 27, 2026 · 4 min read

GT1-6 is the number a billing office calls when a payment fails, and it is one of the easiest fields to get wrong because phone formatting varies wildly from system to system.

Quick answer

GT1-6 is the Guarantor Phone Number - Home field, holding a contact number used specifically for reaching the guarantor at home about billing matters, as distinct from work or mobile numbers carried in neighboring fields.

What this field contains

Format

Telecommunication field — typically digits with optional area code and extension components, though formatting conventions vary by sending system

Scope

Home contact only — distinct from business or mobile phone fields that may appear elsewhere in the same segment

Common variance

Punctuation and formatting — some systems send raw digits, others include dashes, parentheses, or extensions

Example

Synthetic example Generated by Synthibase

GT1|1||DOE^JOHN^R||482 OAK ST^^DENVER^CO^80202|3035550142|||||01|123-45-6789

GT1-6 (3035550142) is a synthetic ten-digit home phone number with no punctuation, one of several formats you should test against.

Where this trips people up

Test suites tend to standardize on one phone format — all digits, or all dashed — because that is what one upstream system happens to send. When a different feed arrives with parentheses, extensions, or international formatting, parsing logic that was never tested against that variation either throws an error or silently truncates the number, and the billing office ends up with an unreachable guarantor.

→

HL7 v2 GT1 Segment Guide: Fields, Format, and Testing Gotchas

→

How to Write EDI Test Cases That Actually Catch Go-Live Failures

→

How to Build a Synthetic Patient Registry for Healthcare Testing

Cover phone-format variation before it hits production

Synthibase generates guarantor phone numbers across multiple realistic formatting conventions, so parsing edge cases surface in testing instead of the billing office.

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This page is written independently by Synthibase for testing and informational purposes. It is not an official publication of HL7 International or X12/Washington Publishing Company, and is not a substitute for reviewing the official standard or your trading partner's companion guide. See our Terms of Service for full legal terms.