Schedule a demo
Healthcare/HL7 v2/OM4
Segment

Observations that require specimens

Carries specimen-related requirements for an observation, including specimen type, collection volume, container description, additive, and specimen handling instructions. It follows OM1 for lab tests and is sent in MFN messages so that collection sites and ordering systems know what specimen is required for each test.

18fields
0required
v2.9HL7 version
om4.py
from zato.hl7v2.v2_9 import OM4
from zato.hl7v2.v2_9 import CWE

om4 = OM4()
om4.sequence_number_test_observation_master_file = '1'
om4.specimen = CWE(
    identifier='SER',
    text='Serum'
)
Python examples

Build OM4 segments in Python

How to construct and work with real-world OM4 segments.

1

Wellness serum separator tube

Lipid panel draw with gel additive, volumes, and cold transport note

from zato.hl7v2.v2_9 import OM4
from zato.hl7v2.v2_9 import CQ, CWE

om4 = OM4()
om4.sequence_number_test_observation_master_file = '1'
om4.derived_specimen = 'N'
om4.container_description = [
    'SST serum separator tube',
]
om4.container_volume = ['5']
om4.container_units = [
    CWE(
        identifier='mL',
        name_of_coding_system='UCUM',
    ),
]
om4.specimen = CWE(
    identifier='SER',
    text='Serum',
    name_of_coding_system='HL70660',
)
om4.additive = CWE(
    identifier='GEL',
    text='Gel separator',
    name_of_coding_system='HL70371',
)
om4.preparation = 'Let clot 30 min upright'
om4.special_handling_requirements = 'Ship at room temp'
om4.normal_collection_volume = CQ(
    cq_1='5',
    cq_2=CWE(
        identifier='mL',
        name_of_coding_system='UCUM',
    ),
)
om4.minimum_collection_volume = CQ(
    cq_1='3',
    cq_2=CWE(
        identifier='mL',
        name_of_coding_system='UCUM',
    ),
)
om4.specimen_requirements = 'Overnight fasting preferred'
om4.specimen_priorities = ['R']
om4.specimen_retention_time = CQ(
    cq_1='48',
    cq_2=CWE(
        identifier='h',
        name_of_coding_system='UCUM',
    ),
)
om4.specimen_handling_code = [
    CWE(
        identifier='CF',
        text='Cold transport',
        name_of_coding_system='HL70376',
    ),
]
om4.specimen_preference = 'P'
om4.preferred_specimen_attribture_sequence_id = '1'
om4.taxonomic_classification_code = [
    CWE(
        identifier='HOM',
        text='Homo sapiens',
        name_of_coding_system='LN',
    ),
]
2

Whole blood fitness panel

Venous draw for exercise physiology markers with routine priority

from zato.hl7v2.v2_9 import OM4
from zato.hl7v2.v2_9 import CQ, CWE

om4 = OM4()
om4.sequence_number_test_observation_master_file = '2'
om4.container_description = [
    'Lavender EDTA tube',
]
om4.specimen = CWE(
    identifier='BLD',
    text='Whole blood',
    name_of_coding_system='HL70660',
)
om4.additive = CWE(
    identifier='EDTA',
    text='K2 EDTA',
    name_of_coding_system='HL70371',
)
om4.preparation = 'Mix gently eight times'
om4.special_handling_requirements = 'Deliver within six hours'
om4.normal_collection_volume = CQ(
    cq_1='8',
    cq_2=CWE(
        identifier='mL',
        name_of_coding_system='UCUM',
    ),
)
om4.specimen_requirements = 'Well-hydrated draw'
om4.specimen_priorities = ['R']
om4.specimen_handling_code = [
    CWE(
        identifier='RT',
        text='Room temp',
        name_of_coding_system='HL70376',
    ),
]
om4.specimen_preference = 'R'
om4.preferred_specimen_attribture_sequence_id = '2'
3

Nutrition screening urine kit

First-morning collection cup with preservative and stability window

from zato.hl7v2.v2_9 import OM4
from zato.hl7v2.v2_9 import CQ, CWE

om4 = OM4()
om4.sequence_number_test_observation_master_file = '3'
om4.container_description = ['Sterile cup']
om4.specimen = CWE(
    identifier='URN',
    text='Urine',
    name_of_coding_system='HL70660',
)
om4.additive = CWE(
    identifier='BOR',
    text='Boric acid',
    name_of_coding_system='HL70371',
)
om4.preparation = 'Label before filling'
om4.special_handling_requirements = 'Keep cool after collection'
om4.normal_collection_volume = CQ(
    cq_1='120',
    cq_2=CWE(
        identifier='mL',
        name_of_coding_system='UCUM',
    ),
)
om4.specimen_requirements = 'Morning void preferred'
om4.specimen_retention_time = CQ(
    cq_1='72',
    cq_2=CWE(
        identifier='h',
        name_of_coding_system='UCUM',
    ),
)
om4.specimen_handling_code = [
    CWE(
        identifier='CF',
        text='Cold transport',
        name_of_coding_system='HL70376',
    ),
]
om4.specimen_preference = 'P'
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
Related segments

Commonly used with OM4

MFI Master file identification MFE Master file entry OM1 General segment OM2 Numeric observation SPM Specimen SAC Specimen container detail
FAQ

Frequently asked questions

OM4 belongs to the observation master file and states what a catalog test expects for collection. SPM appears on patient messages with the actual draw that occurred for a wellness encounter.

Fields 10, 11, and 14 use CQ: quantity in cq_1 and UCUM units in cq_2 as a CWE.

from zato.hl7v2.v2_9 import OM4
from zato.hl7v2.v2_9 import CQ, CWE

om4 = OM4()
om4.normal_collection_volume = CQ(
    cq_1='5',
    cq_2=CWE(
        identifier='mL',
        name_of_coding_system='UCUM',
    ),
)

Field 16 references table HL70920 so interfaces know whether the row describes the preferred tube, an acceptable alternate, or another site-specific ranking for preventive panels.

Field 15 repeats when multiple HL70376 instructions apply, such as room-temperature transport plus a short cold stabilization step before accessioning.

OM4 defines the ideal collection recipe while SAC can carry container level measurements on outbound specimen messages. Together they align master data with operational tracking for wellness programs.

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

OM4 field reference

Complete list of fields in the OM4 segment, HL7 v2.9.

#Python nameDatatypeUsageRepeatableTable
1sequence_number_test_observation_master_fileNMOptionalNo-
2derived_specimenIDOptionalNoHL70170
3container_descriptionTXOptionalYes-
4container_volumeNMOptionalYes-
5▶container_unitsCWEOptionalYesHL70658
6▶specimenCWEOptionalNoHL70660
7▶additiveCWEOptionalNoHL70371
8preparationTXOptionalNo-
9special_handling_requirementsTXOptionalNo-
10▶normal_collection_volumeCQOptionalNo-
11▶minimum_collection_volumeCQOptionalNo-
12specimen_requirementsTXOptionalNo-
13specimen_prioritiesIDOptionalYesHL70027
14▶specimen_retention_timeCQOptionalNo-
15▶specimen_handling_codeCWEOptionalYesHL70376
16specimen_preferenceIDOptionalNoHL70920
17preferred_specimen_attribture_sequence_idNMOptionalNo-
18▶taxonomic_classification_codeCWEOptionalYes-

Ready to build integrations?

Get started with Zato and connect your systems in minutes.

Get started ▶Read the docs
Open source In Python