General rules on measurement unit
Purpose 
A quantitative estimation of a clinical laboratory analyte must be expressed together with an appropriate unit of measurement. Without units, the result is at best useless, at worst dangerously misleading and a great risk to patient care. Many potential forms of measurement unit are available for a given estimation, however the result will be of most benefit to the patient and clinician if the unit is scientifically relevant and commonly employed by local laboratories.  

Recommendation

The International Union of Pure and Applied Chemistry (IUPAC) publishes recommendations for terminology and nomenclature in clinical laboratory medicine in the “Silver Book” (ref. 1). The International System of Units (“SI units” – Systeme Internationale) offers measurement units based on physical quantities and are normally preferable for laboratory estimations in most parts of the world.  
Patient safety

Estimations expressed with no unit create risks for patient management. The recipient of the estimation may assume an incorrect unit, with consequent misinterpretation of the result against a reference or therapeutic interval. Therapeutic drug estimations are an example of how dangerous such misinterpretations may be. A digoxin result of 1.0 nmol/L communicated without units might be assumed to represent a value of 1.0 in mass concentration units (e.g. µg/L). In fact a digoxin value of 1.0 nmol/L is equivalent to a value of 0.8 µg/L. A 20% difference is small enough to increase the risk of error of interpretation not being detected but large enough to risk patient health (e.g. if clinician elected to increase the patient’s drug dosage based on the misinterpreted “low” result). All laboratory estimations, whether communicated verbally, printed report or electronically, must therefore include an appropriate unit of measurement records with the result. 

Reference 

Synonym to measurement unit

Unit, unit of measurement, reference  

Definition of measurement unit

Real scalar quantity, defined and adopted by convention, with which any other quantity of the same kind can be compared to express the ratio of the two quantities as a number (reference 1)  
Scope

Measurement unit is a generic concept of a quantity of any dimension, including nonSI unit and SI unit  
Description 
The specific kindofquantity specifies the type of the corresponding measurement unit, e.g. mmol/L is the corresponding measurement to the kindofquantity, substance concentration. Note: There can be a manytomany relation between the kindofquantity and the type of meaurement unit. Hence, a kindofquantity should be stated in the description of the measurement. Examples The corresponding measurement unit to mass concentration and density can be µg/L or mg/L The corresponding measurement unit to mass fraction or volume fraction can be per mille or one out of thousand (symbol: ‰) 

Reference 

Rule 
Reason 
Example 
One expression per unit 
To ensure unambiguity in reporting values, only one expression for a unit of a given magnitude should be used. Various expressions may cause errors in communication between health personnel and organisations with potential patient mistreatments as consequences  Millimole per liter 
Use multiples and submultiples 
To present numerical values in the interval of 0.1–999 and to make values with very large or very small numerical values readable, the units can be combined with SI prefixes, expressed as either SI prefix symbols or SI prefix factors (numerical values)  
One SI prefix per unit 
To ensure unambiguity in reporting values, only one expression for a unit of a given magnitude should be used. Various expressions may cause errors in communication between health personnel and organisations with potential patient mistreatments as consequences  
One or SI prefix factors are units for dimensionless kindofquantities




Reference 

Scope 
A description of hierarchical categories of units that are graded according to preference  

Description 
Preferable, SI units or internationally accepted nonSI units should be applied. However, due to technical reasons this may not always apply. Prefered units according to a following hierarchical category system:
Note: Internationally accepted nonSI units are traceable to SI units. 

Reference 
