Understanding our data elements

It can be confusing when people refer to the data and coding required to represent laboratory tests.

This is because they could be talking about:

• the name of the test
• the request for the test
• the result of the test
• the unit of measurement relating to a test
• the interpretation of the test
• the diagnosis made from an interpretation of the test
• associated data representing, for example, specimens, body sites or techniques relating to a test
• the entire pathology report

That's not to mention all the other data items included in pathology reporting, such as patient demographic information and laboratory site identifiers. These elements are already being shared across the estate and governed by other information standards.

In our interoperable design, some of the information about a laboratory test is carried inherently in the terminology - for example, SNOMED CT Observable entities carry defining coded attributes relating to measurable characteristic, substance, specimen, and technique. Other data elements are coded separately, using different information standards and data products.

Consequently, here are definitions of the crucial data elements that relate to our terminology and message specification for pathology reporting, referenced throughout our documentation. These are broad definitions to be used in the context of conformance with the DAPB 4101 Pathology and Laboratory Medicine Reporting Information Standard.

Laboratory test result value – a single data item contained in the report, often accompanied by a unit of measure, representing the information determined by making the observation (10 mmol/L for example). Represented by numerics or codes contained in FHIR UK Core value sets or text strings.

Unit of measure (UoM) - a single data item contained in the report accompanying a laboratory test result value. Represented by Unified Code for Units of Measure (UCUM) codes or text strings.

Laboratory test result interpretation - a single data item contained in the report, representing a categorical assessment of an observation value (high/low/normal for example). Represented by codes contained in FHIR UK Core value sets or text strings.

Laboratory test specimen – a single data item contained in the report identifying the specimen upon which the test was performed. Represented by SNOMED CT Specimen/Substance/Morphologic abnormality/Body structure/Physical object concepts or text strings.

Laboratory test request code - colloquially known as ‘requestables’, these identify the specific laboratory test(s) initially requested that led to the generation of results. Represented by SNOMED PaLM Requestables.

These data elements will be represented using text strings in the initial implementation of DAPB 4101. Use of codes will be mandated following updates to the Standard.

Quantitative result

The result is expressed as a number, usually with an associated unit of measure. Comparators may be used to indicate that the actual value is greater than or less than the stated value. A range of values may be reported instead of a single value.

Examples of quantitative test results include:

• Albumin: 47 g/L
• eGFR: >90 mL/min/1.73m2

Semi-quantitative result

The result is expressed using a descriptor to indicate the relative degree of positivity or negativity based on a scale. The scale is not always formally defined. Semi-quantitative results are widely used in microbiology, particularly for reporting microscopy and culture test results to indicate the amount or level of growth of organisms.

Examples of semi-quantitative test results include:

• Epithelial cells: +
• Organism susceptibility to nitrofurantoin: Resistant  

Qualitative result

The result is expressed using a descriptor to indicate positivity or negativity. The descriptors are usually defined as pairs, for example: positive/negative, detected/not detected, isolated/not isolated. In this respect, qualitive results can be seen as a subset of semi-quantitative results in that they contain only two scale points to indicate positivity or negativity.

Examples of qualitative test results include:

• Hepatitis B surface antigen: NEGATIVE
• MRSA screening test: NOT DETECTED

Quantitative result combined with an interpretation

In some cases, a result may contain a combination of quantitative and non-quantitative elements. The non-quantitative element is sometimes expressed separately as an interpretation to provide a categorical assessment of the quantitative value.

Examples include: 

• Lymphocyte count: 0.70 10*9/L  LOW
• Rubella IgG antibody: >10 IU/ml  DETECTED

Narrative result

The result is presented as text. For example:

• Aerobic culture: No growth detected after 5 days incubation

Detailed guidance on how result values are represented in DAPB4101 conformant pathology reports is available in the Pathology FHIR Implementation Guide.