Rules for use of SI-prefixes

by | Feb 6, 2020 | NPU Concept model, Measurement units

Rules for use of SI-prefixes in laboratory medicine

Definition SI prefixes are a set of multiples and submulitples within the SI system
Purpose of the use of SI-prefixes

To prevent communication errors due to several expressions of the same unit

To ensure that the numerical values in laboratory results are human readable and understandable
Principles
  • One expression of a unit
  • Numerical values of laboratory measurements should be presented in the range of 0.1-999 (Ref 1)
  • Units for quantities of the same sort of system, sort of component(s), and kind-of-quantity should differ at least by a factor of one thousand to avoid confusions of unit and prefix symbols
  • A unit can be a SI factor (a number as sub- or multiples)
Rules
  • Unit of a given magnitude should only have one expression
  • One SI prefix per unit
  • SI prefix belongs in the numerator only
  • One thousand between SI prefixes (deci (d), centi (c), deca (Da), and hecto (H) are not allowed)
Reference
  1. Health informatics. Expression of results of measurements in health sciences. EN 12435:2006, 6.13
  2. Hansen YBL. Recommendations on Measurement Units – Why and How. EJIFCC. 2019;30(3):250-75.
  3. https://www.bipm.org/en/measurement-units/

 

Factor Term Symbol
10–24 yocto y
10–21 zepto z
10–18 atto a
10–15 femto f
10–12 pico p
10–9 nano n
10–6 micro µ
10–3 milli m
103 kilo K
106 mega M
109 giga G
1012 tera T
1015 peta P
1018 exa E
1021 zetta Z
1024 yotta Y

Note: SI prefixes (deci (d), centi (c), deca (Da), and hecto (H) are not allowed or displayed

Principle

One expression per unit
Background A unit can be expressed in several combinations. It is to avoid confusion about different expressions of the same unit.
Examples

Rules

 One SI prefix per unit

  • SI prefix belongs in the numerator only
Reference
  1. Health informatics. Expression of results of measurements in health sciences. EN 12435:2006, 6.13
  2. Hansen YBL. Recommendations on Measurement Units – Why and How. EJIFCC. 2019;30(3):250-75.
  3. https://www.bipm.org/en/measurement-units/

 

Preferred unit term Examples of non-recommended unit terms
SI factor Gram Litre Mol Factors (number)
10–12                        
10–9            
10–6            
10–3                        
1                        
103                        
106                        
109                        
1012