UCUM composition

The Trauma registry project has a case for recording quantity of blood transfused.

In the source specification, the reporter may record quantity as mL or as “units.” If units, there is a separate question to clarify the volume of a “unit” in that context (which may vary by facility, age of recipient, blood product, etc.), in mL.

We suggested that if the reporter is recording both the number of units and the mL/unit, it would be a simpler matter to record one calculated measure in mL than to record two facts, one a measure in an idiosyncratic unit and one a definition of the unit. However, there may be some inflexibility on this point.

In case there is, we read UCUM to permit the prefix of a quantity, so that if a reporter records “5 units at 300 mL/unit,” one might record a PQ of 5 (unit = “1”) and a separate observation of the size of the unit, being a composition of magnitude and unit, e.g “300.mL” (with a period signifying multiplication). In this case, the second observation would presumably have a magnitude of 1 and a unit of “300.mL”.

Alternatives might be 3.102.mL (but I have not seen scientific notation examples with any values other than powers of 10) or 102.477121255.mL (but I don’t think the decimal of log(300) can be distinguished from the multiplicative operator “.”)

I have not seen this done, and would like confirmation I’m on the right path.