HL7 Table HL70136: Y/N Indicator

HL70136 is the simplest possible HL7 code table: two values, Y and N. It is used everywhere v2 needs to carry a boolean — donor eligibility flags, pregnancy indicators, medication-component overrides, insurance assignment-of-benefits, and dozens of other fields across nearly every segment. The table has been HL7-defined since v2.1 and has never changed.

Purpose

HL70136 carries a yes/no decision that cannot meaningfully be represented as unknown. It is intentionally distinct from richer boolean-like tables (HL70532 Expanded Yes/No Indicator, which adds U/NA/NASK) — when HL70136 is the bound vocabulary, "unknown" is not a valid response and the sender must commit to one of two values.

The simplicity is the point. Engines that try to overload HL70136 with U, ?, or empty-string semantics break receivers that follow the v2 standard literally. If unknown is a real possibility, the bound vocabulary should be HL70532, not HL70136.

Where it's used

A non-exhaustive list of fields bound to HL70136 in v2.8.1:

DON-9 Donor Eligibility Flag
DON-15 Intended Recipient Blood Relative
DON-27 Donor Reaction
DON-29 Final Review Staff ID exists
PID-32 Identity Reliability Code
RXC-7 RX Component Override
IN1-20 Coordination of Benefits Indicator
IN1-32 Patient Signature Source
PV2-12 Visit Publicity Code
OM1-12 Confidentiality Code
ROL-9 Provider Organization Unit Type
ACC-9 Auto Accident State (yes/no jurisdiction flag)

The table is referenced from many more fields; the binding is recognizable by the field's data type (ID length 1) and the table reference in the v2 specification.

Code list

Code	Display	Comment/Description
Y	Yes	The condition or attribute applies.
N	No	The condition or attribute does not apply.

Code system OID

OID: 2.16.840.1.113883.18.66
Canonical URI: http://terminology.hl7.org/CodeSystem/v2-0136

The OID is rarely emitted because HL70136-bound fields are almost always ID rather than CWE; CWE-bound variants (HL70532) carry the OID for the expanded set, not for HL70136 itself.

HL7-defined vs user-defined

HL70136 is HL7-defined and not extensible. Sites that need a third value (Unknown, Refused, Not Applicable) should use HL70532 Expanded Yes/No Indicator on a CWE field rather than adding codes to HL70136.

Version differences

v2.1 – v2.8.1 — Two values, no changes.
v2.5 — HL70532 introduced as the richer alternative for fields where Unknown is a meaningful answer. HL70136 retained where binary semantics are sufficient.

Common mistakes

Sending 1/0 or T/F instead of Y/N. The codes are letters, case-sensitive uppercase.
Sending an empty string when the intent is N. Empty means "not stated"; explicit N means "no, this is not the case". Many receivers treat the two differently.
Confusing HL70136 with HL70532. The two-value table is for fields where unknown is genuinely not a meaningful answer; the three-value expanded table is for everything else.
Defaulting unknown values to N to avoid a null. If the answer is unknown, the field should be left empty (or use HL70532 where bound), not falsely populated as N.

Examples

A donor segment indicating eligibility and a positive blood-relative flag:

DON|1||20260610|||||||Y^Yes^HL70136|||||Y^Yes^HL70136

An insurance segment with assignment of benefits:

IN1|1|BCBS001|...|||||||||||||||||Y^Yes^HL70136

Same Y value translated to a FHIR boolean:

{
  "resourceType": "Coverage",
  "id": "cov-10456",
  "subrogation": true
}

Mapping failure example — vendor sends an unknown-style value:

DON|1||20260610|||||||U

U is not in HL70136. A conformant engine should route to curation. If the field is genuinely intended to carry unknown semantics, the channel should be upgraded to HL70532, where U is a valid value.

FHIR mapping

The v2-to-FHIR IG does not publish a ConceptMap for this table; the mapping below follows the obvious correspondence:

HL7 v2 (HL70136)	FHIR (boolean)
Y	true
N	false

Absent/empty HL70136 fields map to absent FHIR elements, not to false. Round-trip is lossless.

Engine considerations

Case sensitivity — Both codes are uppercase. Normalize lowercase variants on ingest.
Empty vs explicit N — Preserve the distinction between empty and N when mapping to FHIR; emit false only for explicit N, leave the element absent otherwise.
HL70532 upgrade path — If a receiver needs unknown semantics, route through an HL70532-bound CWE field rather than overloading HL70136.
No display string — Y^Yes^HL70136 and bare Y are equivalent on ingest; engines should accept both.

How Vorro handles HL70136

Vorro validates HL70136-bound fields against the two-value set on ingest and normalizes lowercase variants to uppercase. Empty values pass through as null; explicit N is preserved as N so downstream systems can distinguish "no" from "not stated".

On outbound FHIR, Vorro emits true for Y and false for N, and leaves the boolean element absent when the source field was empty. The original HL70136 code is not preserved as an extension because the round-trip is information-preserving without one.

Sources

← Back to HL7 v2 Guide