Example 5 - Screening for MRSA

Screening tests differ particularly in their approach of pathogen detection, and involve a targeted search for pathogens. For example, molecular diagnostics are specifically performed to detect MRSA by detecting resistance genes or proteins.

Accordingly, for MRSA screening, a LOINC code is selected according to the research questions of the test kits used, which specifically asks for the presence of a mecA or mecC gene or the PBP2a protein.

• In the first example, a PCR is performed that tests for the presence of Staphylococcus aureus DNA and the resistance genes mecA and mecC in one step. It must be possible to represent the results for the detection of Staphylococcus aureus DNA and the detection of the mecA or mecC genes independently of each other in the illustration of this diagnostic test. With the profile for the "observation" for ARS presented in this pilot phase, it is necessary to represent the test result in two "observations": one "observation" to describe the pathogen detection and one or more "observations" to describe the resistance gene detection.
  • To determine whether Staphylococcus aureus DNA is detectable, a LOINC code with the "property" [PrThr] is used, which is answered with "detected" or "not detected." This observation refers to the "specimen".
  • At the same time, a second "observation" asks about the detection of an MRSA resistance gene. In accordance with the rules for handling semantics, a LOINC code is used, which asks about the presence and type of the resistance gene.
• In the second example, the detection of "PBP2a" protein using latex agglutination is presented as another method used in MRSA screening. In this method, "PBP2a" protein is either detected or not; accordingly, a LOINC code with the "property" [PrThr] was chosen, to which the answer can be "positive" or "negative".

The starting specimen in both examples is a groin swab. The specimen arriving at the laboratory should be described  in the "Specimen" resource under Specimen.type. The specimen can be used either as a groin swab with the code "445444005 Swab of inguinal region (specimen)" as shown in the first part of this example, or as a swab with the code "257261003 | Swab (specimen)" under Specimen.type and, additionally, the groin as the collection site with the code "26893007 | Inguinal region structure (body structure)" under "Specimen.collection.bodySite", as shown in the second part of this example. Both representations are equally valid for ARS.

The LOINC code used in the example for the detection of PBP2a must be requested.