Implementation guide for interoperable medicines

This guidance is under active development by NHS England and content may be added or updated on a regular basis.

Units of Measure

A unit of measure is required when describing a dosage and can be supplied via one of two code systems:

Preferred: Unified Code for Units of Measure (UCUM)

The Unified Code for Units of Measure (UCUM) is preferred and should be used where possible.

Examples of when a UCUM unit of measure would be used are:

  • gram (g)
  • milliliter (ml)
  • percent (%)

e.g.

<quantity>
    <value value="12.5" />
    <unit value="milliliter" />
    <system value="http://unitsofmeasure.org" />
    <code value="ml" />
</quantity>

Alternative: SNOMED-CT

In the instance where a UCUM unit of measure is not defined, use a SNOMED-CT unit of measure instead. All units of measure are descendants of concept 767524001 | Unit of measure (qualifier value) which includes both UCUM and non-UCUM codes.

Examples of where a SNOMED-CT unit of measure would typically be used include:

  • tablet
  • capsule
  • ampoule
  • patch

At this time, there is some overlap within SNOMED-CT for non-UCUM codes within descendants of 732935002 | Unit of presentation (unit of presentation) and 408103002 | Unit of drug administration (unit of presentation).

Both these hierarchies include units such as tablet therefore as a provider/sender system, either code can be used, and as a consumer/receiver system, either code can be received and accepted.

For example

<quantity>
    <value value="2" />
    <unit value="tablet" />
    <system value="http://snomed.info/sct" />
    <code value="428673006" /> <!-- from "Unit of drug administration" --> 
</quantity>

Or

<quantity>
    <value value="2" />
    <unit value="tablet" />
    <system value="http://snomed.info/sct" />
    <code value="732936001" /> <!-- from "Unit of presentation" -->
</quantity>
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