Insulin Units and Conversion Factors: A Story of Truth, Boots, and Faster Half-Truths.

Conventional insulin concentration units (IU/mL or just U/mL) are bioefficacy based, whereas the Système International (SI) units (pmol/L) are mass based. In converting between these two different approaches, there are at least 2 well-accepted conversion factors, where there should be only 1. The correct value is not the most-used or well-accepted using online calculators, some journal styles, laboratory reports, and published articles. In short, an incorrect insulin conversion factor is widely used which underreports insulin concentrations by ~15%, with potentially significant research and clinical implications. This short commentary describes the history of insulin IU definitions and conversion factors, and highlights the widespread nature of conversion factor misuse, to provoke deeper interest and thought regarding numbers we so often use without thinking.

The story of the gauge.

Gauges are old measures of thickness. They originated in the British iron wire industry at a time when there was no universal unit of thickness. The sizes of the gauge numbers were the result of the process of wire-drawing and the nature of iron as a substance. Gauges were measured and described in fractions of an inch during the 19th century. In the UK, one gauge was standardised and legally enforced as the Standard Wire Gauge. One important reason for the standardisation of the gauge was the convenience of craftsmen. In the 20th century, the gauge was to be replaced with the introduction of the International System of Units. However, within the field of anaesthesia at the threshold of the 21st century, the gauge seems hard to remove from the minds of craftsmen like anaesthetists.

El Sistema Internacional de Unidades / The International System of Units

A través de los años, diversas organizaciones internadonalmente reconocidas, han creado e implantado el Sistema Internacional de Unidades: un sistema métrico de medición basado en solo siete unidades bdsicas. De estas unidades básicas se derivan muchas más. El Sistema Internacional de Unidades es solo el comienzo del aseen· so de una tendencia de cambio del las unidades con ven· cionales esparcidas a un sistema de medición mundial.

Scientific medicine and Système International units.

The Système International, a modern version of the metric system, is being introduced into American medicine. The most compelling reason for this is that a worldwide standardization of weights and measures is taking place, and American medicine should take part in this process. A subsidiary advantage is that units of measurement used in clinical laboratories throughout the United States will be standardized as well. It is possible that expressing concentrations in moles per liter rather than as weight per volume will reveal clinically useful chemical relationships, but this remains unproved. Transition to Système International units will require use of different reference ranges, and there will be a potential for serious misinterpretation of laboratory data unless well-planned educational programs are instituted before the change.