Specimen Type 66746-9 vs Specimen Source 31208-2?

What is the difference between these two LOINCs, and why should I choose one over the other?

66746-9 Specimen type:Type:Pt:Specimen:Nom

31208-2 Specimen source:Prid:Pt:XXX:Nom


Hi Doug,

Excellent question. You’ll see 31208-2 has the highest usage noted from the Common US Lab Results ranking (note the ranking hasn’t been updated for close to a decade). It’s been around since v2.07 (a long time). A Presence or Identity property tied to a Specimen Source component indicates the result value is the name of where the specimen came from. There’s not an example answer list with this term. It might denote the location a sterile swab was procured for a culture or antigen detection.

66746-9 on the other hand has information on the details page; there’s a term description and an example answer list. While they may seem identical, I’ll suggest examples to segregate the nuances…

A specimen type may be a wound, while the specimen source may be left upper shoulder.

A specimen type may be synovial fluid, while the specimen source may be right knee.

Hope this helps!


Thanks Pam for the quick reply. This has been bugging me for some time now. The type vs source terminology isn’t necessarily standard - at least in my brain. 66746-9 has some nice documentation on the LOINC search details page, but 31208-2 not so much.

To map this to OBR-15 or SPM then:

66746-9 would go in OBR-15.1 and SPM-4

31208-2 would go in OBR-15.4 and SPM-8

Or put another way, 66746-9 is what you’d send if this is the only specimen information you wish to send. It’s the main specimen observation.

31208-2 is additional (body site?) information you’d send about a specimen, but it should really be a qualifier for 66746-9 (or its proper HL7 field equivalent).



Good questions. Specimen Types and Sources are often confused.

A Specimen Type is “what is collected, often transported to teh lab in a specimen container”. It is mapped to SNOMED CT Specimen hierarchy codes for use in US lab messages in the SPM 4 segment for HL7 LOI, LRI, ELR, and HAI implementation guides (and also used in FHIR). It may have a modifier in SPM 5 mapped to a qualifier value SNOMED CT code. These modifiers may be for a post convalescent specimen, or post transfusion reaction specimen.

Specimen Source on the other hand, is the Anatomic Site from which a specimen is collected (where on the body such as for a swab specimen for a wound culture). It is messaged in the SPM 8 field and mapped to a SNOMED CT anatomic body site code (per the LOI, LRI, ELR, HAI guides). It may have a modifier (i.e. Left with a source of Arm) in the SPM 9 field mapped to a SCT qualifier code. FHIR also supports body site.

From your ask, suspect you may have a lab order and results built (such as for many pathology, microbiology, genetics tests) where the order doesn’t specify the specimen or it’s a bit more generic like body fluid, tissue, or any/multiple specimens can be analyzed such as represented in XXX LOINCs. In that case, you may have an Ask at Order Entry (AOE) Question where the person collecting the specimen is required to indicate what the specimen type is or where it was collected from (specimen source). In this case “Specimen Source?” would be mapped to LOINC <span style=“background-color: #fbfbfb; font-family: Lato, Helvetica, Arial, Lucida, sans-serif; font-size: 15.6px;”>31208-2 as you indicate. The value/response sent to the lab and usually reported back as it’s own lab result would be mapped to teh SNOMED CT code(s) as applicable. In some cases, the specimen collection procedure is warranted and messaged in SPM 7 (such as biopsy, venipuncture, etc) and mapped to a Specimen procedure code.</span>

To answer your question on choosing between them, it depends which of the two definitions/contexts apply. Consider the following. For the Wound Culture, a swab is taken of the left ear from an infected piercing. “Ear” is the source. However, if the patient was in a sword fight and lost their ear and it was submitted to pathology as specimen type for analysis, then “Ear” is a specimen. For human and computer usability the different SNOMED CT codes provides the different contexts. Many LISs and EHRs also represent these terms in different dictionaries supporting one of the SCT hierarchy maps or the other so they are distinct. Also the terms are used to populate the appropriate HL7 message fields appropriately. I have seen labs mix the two up so “head,” “neck,” or “back” terms are listed as specimen types. However, they can only be submitted once on a patient and it’s likely from an autopsy procedure. It would be more common to see these as specimen sources (for micro/cultures, genetics, etc.)

Some of the newer LOINC User Guides such as micro also discuss these codes/terms.