Research concepts
Micrograms, milligrams and international units
Micrograms, milligrams and international units: Am I converting mass units or comparing mass with activity?
Source editorial review:
Before interpreting the result
Am I converting mass units or comparing mass with activity?
- Keep mg, µg and IU distinct on the label and in the record.
- Identify the substance, assay and standard when activity is reported in IU.
- Separate total mass, species content and measured activity.
Micrograms, milligrams and international units
Micrograms and milligrams express mass and have a defined conversion. International units are tied to relevant activity or reference preparations and provide no universal conversion to mass for every substance. Present mass and molecular identity are also different questions: oxidation or deamidation can change species mass, while some isomers can preserve it.
A reading case: what to check
When transferring a quantity into a record, first preserve its original unit. Document the relation used for mass conversion. Converting international units to mass requires a valid relation for the relevant material and standard, not one borrowed from another compound. Commercial mass quantity also does not establish biological potency without the corresponding measurement.
What to preserve in the record
Converting mg to µg is arithmetic; converting mass to IU needs a specific documented relationship. Weighing a sample does not establish its constituent species or activity.
Questions and answers
Am I converting mass units or comparing mass with activity?
Micrograms and milligrams express mass and have a defined conversion. International units are tied to relevant activity or reference preparations and provide no universal conversion to mass for every substance. Present mass and molecular identity are also different questions: oxidation or deamidation can change species mass, while some isomers can preserve it.
What should the review record preserve?
Converting mg to µg is arithmetic; converting mass to IU needs a specific documented relationship. Weighing a sample does not establish its constituent species or activity.
Sources
- Consensus statement on the standardization and evaluation of growth hormone and insulin-like growth factor assays.
- The First International Standard for Somatropin: report of an international collaborative study.
- The International Standard for Human Growth Hormone for Bioassay: calibration and characterization by international collaborative study.
- In vivo bioassay for the potency determination of human growth hormone in dwarf "little" mice.
- Selective quantification of the 22-kDa isoform of human growth hormone 1 in serum and plasma by immunocapture and LC-MS/MS.