Jim, it is weird. Call it an American affectation. From what I can gather from my brief study of medical laboratory science, there is a US use of laboratory units that differs from those in the rest of the world. I think the difference lies in the perception in the US that if SI *BASE* units are used in expressing the concentration of the substance being measured, the LABORATORY units are considered to be SI, while the units used in the US are "not" SI. I think that if they knew what they were talking about, they would say "non-US," not "non-SI." Actually, I think (I could be wrong) that the US units are called either "US" or "standard."
For example, the unit used to measure blood glucose in American labs is mg/dL, while outside the US, it is mmol/L. Blood glucose meters usually have a switch on them to allow the patient to toggle betwee mg/dL and mmol/L, presumably depending upon the country of usage. So, it is SI to them only if they use an SI base unit (mol) in the numerator of the concentration. Nyuk, nyuk, nyuk. It just seems to me the keepers of the medical laboratory units may need to brush up on how SI is applied. Paul Trusten, Reg. Pharmacist Vice President U.S. Metric Association, Inc. Midland, Texas USA www.metric.org +1(432)528-7724 trus...@grandecom.net On May 19, 2013, at 15:55, James Frysinger <j...@metricmethods.com> wrote: > I was doing some research for my sister's use of vitamin B12 supplements and > came to this page: > http://www.webmd.com/diet/vitamin-b12-15239?page=2 > > It contains a small chart: > Vitamin B12Normal: > More than 200-835 picograms per milliliter (pg/mL) > 148-616 picomoles per liter (pmol/L) (SI units) > > Interestingly, WebMD apparently considers picomoles per liter to be in SI > units but picograms per milliliter not to be in SI units. > > Of course, the non-SI unit is the liter (or milliliter) but that's acceptable > for use with the SI. So, in my mind neither value statement is "more SI" than > the other. > > How do you view this, Paul Trusten? > > Jim > >
