Message type

Tabular response - site defined

Returns a tabular query response. The QAK segment reports the query status, QPD echoes the parameters, and RDF/RDT segments carry the table definition and row data.

9segments

5required

0groups

v2.9HL7 version

# Zato
from zato.hl7v2 import HL7Message

# An incoming message ..
raw = 'MSH|^~\&|SENDER|FAC|RCV|DEST|20260701||' \
      'RTB^Knn^RTB_Knn|MSG001|P|2.9\r' \
      'QAK|QRY001|OK|Q22\r' \
      'QPD|Q22^FindCandidates|QRY001|SMITH^JOHN'

# .. parsed into a Python object ..
msg = HL7Message.parse(raw)

# .. whose fields we can now access.
query_tag = msg.qak.query_tag
status = msg.qak.query_response_status
query_name = msg.qpd.message_query_name
query_tag = msg.qpd.query_tag

Python examples

Build and parse RTB^Knn messages in Python

How to construct, send, receive, and extract fields from real-world RTB^Knn messages.

Parse an incoming RTB^Knn message

Demonstrates receiving and extracting key fields from a tabular response - site defined transaction

# Zato
from zato.hl7v2 import HL7Message

# An incoming message ..
raw = 'MSH|^~\&|SENDER|FAC|RCV|DEST|20260701||' \
      'RTB^Knn^RTB_Knn|MSG001|P|2.9\r' \
      'QAK|QRY001|OK|Q22\r' \
      'QPD|Q22^FindCandidates|QRY001|SMITH^JOHN'

# .. parsed into a Python object ..
msg = HL7Message.parse(raw)

# .. whose fields we can now access.
query_tag = msg.qak.query_tag
status = msg.qak.query_response_status
query_name = msg.qpd.message_query_name
query_tag = msg.qpd.query_tag

Tutorials

Learn by building

Step-by-step guides for working with HL7 v2 in Zato.

MLLP

Receive and parse HL7 v2 messages

Set up an MLLP channel, parse incoming messages, and respond with acknowledgments.

Start tutorial Build

Build and send HL7 v2 messages

Construct HL7 v2 messages from scratch using typed segment classes and send them over MLLP.

Start tutorial

FAQ

Frequently asked questions

Use the HL7v2 message parser to extract the typed structure. The parsed message gives you direct access to every segment and field by name.

from zato.hl7v2 import HL7Message

raw = 'MSH|^~\&|SENDER|FACILITY|RECEIVER|DEST|20260401120000||RTB^Knn^RTB_Knn|MSG00001|P|2.9\rMSA|AA|MSG00001\rERR|||0|I|\rQAK|QRY-2001|OK\rQPD|QRY-1001|QRY-2001|\ranyHL7Segment|\rDSC|CONT-001'
msg = HL7Message.parse(raw)

ack_code = msg.msa.acknowledgment_code
control_id = msg.msa.message_control_id

Beyond the mandatory MSH header, the required segments are: MSA, QAK, QPD, anyHL7Segment. Optional segments provide additional detail when available.

Zato connects to any system that speaks HL7v2 over MLLP or FHIR over REST. This includes Epic, Cerner, Meditech, Allscripts, and other EHR platforms.

Yes, Zato has built-in MLLP support for sending and receiving HL7v2 messages. MLLP channels handle the framing protocol automatically.

Zato supports HL7 v2.9, which is backward compatible with earlier versions including v2.3, v2.5, and v2.7. Standard segments and datatypes are available as typed Python classes.

Yes. Zato handles both HL7v2 and FHIR natively, so you can parse v2 messages and build FHIR resources with IG-specific extensions in the same service. Typed Python classes are available for both protocols, including extensions from US Core, UK Core, Da Vinci, and other Implementation Guides.

Reference

RTB^Knn segment composition

Segments that make up the RTB^Knn message, in order. Groups are shown with their child segments.

#	Segment	Usage	Repeats	Description	Group
1	`MSH`	Required	No	Message header	-
2	`SFT`	Optional	Yes	Software segment	-
3	`UAC`	Optional	No	User authentication credential	-
4	`MSA`	Required	No	Message acknowledgment	-
5	`ERR`	Optional	No	Error	-
6	`QAK`	Required	No	Query acknowledgment	-
7	`QPD`	Required	No	Query parameter definition	-
8	`anyHL7Segment`	Required	No	anyHL7Segment	-
9	`DSC`	Optional	No	Continuation pointer	-

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Open source In Python