Log in Register

The LOINC Part XXX: Going PG

The letter “X” can stand for so many things. “X” marks the spot on a map! “X” in Xmas is sometimes used as an abbreviation for Christ. X’s and O’s mean kisses and hugs in letters of admiration. Three X’s in baseball expresses a “Strike! You’re OUT!” X as a roman numeral stands for 10. One specific significance of the letter X is that it symbolizes the unknown, something vague, or a variable.

How do coding systems deal with an unspecified situation/condition? SNOMED CT has several “unspecified” qualifiers. CPT and ICD-10-PCS code systems, which are primarily used for billing, have terms that do not identify a specific specimen or use the word “other”, “not otherwise specified”, or “unspecified” in the phrase to denote the specimen’s anonymity. These billing codes act as bigger buckets for less commonly named specimens. Early in the development of LOINC, the committee thought they’d use a placeholder of XXX for the attribute that wasn’t specified. Thus, “XXX” is used as a LOINC part in different axes of the LOINC name. It can be used in the Time Axis or the System Axis. Here are some examples: PuzzleQuesMark400

  • Time axis: 35663-4 Protein:MCnc:XXX:Urine:Qn:
    Most lab tests are PT (point in time). This means that they are measuring the amount of analyte present in a given sample at the time of collection. XXX is used when your IMPLEMENTATION uses the same result field for random urine and timed urine collections.
  • Specimen/System axis: 43714-5 Adenovirus Ab:PrThr:Pt:XXX:Ord:
    LOINC uses a System of XXX for terms where either the specimen is truly unknown (e.g. a solid or liquid that is not otherwise identified) or is expected to be specified in a field other than the LOINC name.
    Although XXX has been around for a while, new adopters of LOINC have found it difficult to decide when it could be used. This issue was brought up in LOINC’s April 2020 call and again during the LOINC virtual conference in October during a LOINC Committee meeting:
  • Reference ranges for measures on a contiguous scale change with specimen differences (most systems depend on the test code to get the reference ranges)
  • The nature of the specimen can affect the clinical implications for some organisms (for example: natural inhabitants of skin/digestive system versus a transient species/invader)
  • A generic specimen in the test name may make it harder to order common microbiology tests (no one click solution)
  • Labs tend to define tests for class of specimens approved for use on the instruments/test kits they employ, so “XXX” may not be approved

So, what does XXX really mean? Here are some points to keep in mind:

  1. Myth: The test can be run on anything.
    Truth: Laboratories have to validate different specimens against other methodologies and equipment to assure an assay can be run on a particular specimen type.
  2. Myth: No one (including the lab reporting the result) knows what the sample was.
    Truth: Laboratories certified to run in the US do not run a specimen without finding out the source. In toxicology, where unknown residue may be submitted, there is a LOINC term for ‘Unknown substance.’
  3. The test can be run on a specified set of samples that are not currently a defined LOINC system (for example: Ser/Plas/Synovial Fluid)
  4. The LOINC code doesn’t specify what sample the test was run on, but it will be specified elsewhere. In fact, the most commonly used LOINC term is Specimen Source, so they are tying another result field to the XXX assay field.

To help reduce the confusion, LOINC is taking XXX out of the Long Common Name, Short Name and Display Name fields of the LOINC database. When you see an XXX attribute, you’ll find a display of “in Specimen”. Example:

LOINC Code: 47121-9
Long Common Name: Mercury [Moles/mass] in Specimen
Short Name: Mercury Spec-sCnt
Display Name: Mercury (Specimen) [Moles/Mass]
Consumer Name: Mercury, Specimen

To figure out if you should use XXX in a LOINC term, think of assays offered where the same kit/reagent is used for different specimen types; you may have a prompt field at order entry of Specimen; you may have a different kind of label print out. The Mercury example above would cover hair/skin/nail clippings. If your lab only accepts nail clippings for the heavy metals, you would be using the nail specific LOINC terms instead.

 

Please contact us if you have questions or suggestions for future topics of discussion, or for help implementing or mapping to standard terminologies.