Missing required child OML_O21_ORDER_PRIOR.OML_O21_OBSERVATION_PRIOR

[mungra]

Hi,

How can i parse OML message strings with multiple ORC group without prior obx using strict validation (required).
exception : Missing required child OML_O21_ORDER_PRIOR.OML_O21_OBSERVATION_PRIOR

setting find_groups=False gives me different exception : PID is not a valid child for which doesnt make sense.

MSH|^~&|ClinicSystem|MainClinic|LaboratorySystem|MainHospital|20250709160000||OML^O21^OML_O21|MSG00028|P|2.7||||||||||
PID|1||GP-000001^^^^MR||Doe^John||19801029|446151000124109^Male^SCT||||||||U^Unknown||||||||N||||||||||||||||
ORC|NW|LAB123456|ORD987654|||||||98765^Doe^John
OBR|1|LAB123456|ORD987654|1234^Complete Blood Count^L|||20250709160000|||||||||98765^Doe^John
NTE|1|L|Sample collected in the morning.
ORC|NW|IMG123456|ORD987655|||||||98765^Doe^John
OBR|2|IMG123456|ORD987655|5678^Chest X-Ray^L|||20250709160000|||||||||98765^Doe^John
NTE|2|L|Patient has a history of asthma.

using hl7 v2.7

try:
    cleaned_message = message.replace('\r\n', '\r').replace('\n', '\r')
    return parse_message(cleaned_message, version="2.7", validation_level=VALIDATION_LEVEL.STRICT, force_validation=True, find_groups=True)
except HL7apyException as e:
    raise Exception(f"Invalid HL7 message: {e}")

Regards,
Mungra

[asulis]

Dear Mungra,

this error is due to an ambigous structure that the specfic OML_O21 message has, in terms of message blocks. Looking at the sequence of segments in the message, the second ORC-NTE-OBR group of segments in the message could either be enterpreted as a second ORDER group (as it is in this specific use case) or as the beginning of a PRIOR_RESULT block. This second interpretation is exactely the one made by the parser. Now, the problem is that OML_O21_ORDER_PRIOR.OML_O21_OBSERVATION_PRIOR is effecly mandatory, so this is why the validation fails.
Unfortunately there is no way to distinguish the two different structures (multiple ORDER groups or one ORDER group followed by a PRIOR_RESULT), so the only thing you can do here is disable validation and put find_groups to false, in a way to parse the message properly.

Hope this helps, best regards
Alessandro

[mungra]

Thank you Alessandro for your reply. Yes this helps. quick question, would another workaround be the use of custom message profiles? We haven't used it yet but did see the option in hl7apy.

thanks and regards,
Mungra