Skip to main content

mmol/l to mg/dl and back again...Why's it 18 times?

I posted this around 10 years ago, but now I have a whole new set of followers, thought I'd post it again!

Americans use mg/dl as the unit for measuring glucose levels. Most other countries use mmol/l. The relationship between the two is that 1mmol/l = 18mg/dl. I was interested to understand this relationship (as a former chemist) and also find out what it meant in practical terms. It is a bit sad, but here is my calculation:

The unit mmol/l stands for milli-moles per litre. (or liter in the US). milli means a thousandth, so what is a mole (other than a small rodent-like animal)? A mole is that quantity of a substance whose mass in grams is the same as its formula weight (atomic weight). Each molecule of glucose has 6 Carbon atoms, 12 Hydrogen atoms and 6 Oxygen atoms. A carbon atom weighs 12 units, a hydrogen atom weighs 1 unit and an oxygen atom weighs 16 units. These units are called relative atomic mass units (don't need to go into why). So the atomic weight of glucose is (6x12) + (12x1) + (6x16) = 180. Therefore one mole of glucose weighs 180g. So now we are in a position to look at mmol/l. 1 mmol of glucose is 0.18g. So 1 mmol/l is 0.18g in 1 litre of water.So now you can see the relationship to mg/dl. A decilitre is a tenth of a litre or 100ml. A miligram is a 1000th of a gram. Therefore 0.18g is the same as 180mg. We are only dealing with a 10th of the amount of water (100ml or 1dl) so therefore can divide this number by 10 giving 18mg/dl. Thus 1 mol/l = 18 mg/dl.

Finally, for those who are interested in how sensitive our glucose meters are, think about this. Mine does graduations in 0.1 mmol/l increments. As shown about 0.1mmol is 0.018g. I think it is remarkable that I have a handheld, portable device that can tell me differences of 0.018g of a substance in a litre of liquid! Probably bored you silly, but I didn't know why this relationship existed until I sat down and calculated it, so at least I have learnt something!

One more thing has struck me. How many grains of sugar is 0.018g? After some research, I think I may have found the answer. According to a site I have found, the density of granulated sugar is 849kg/meter cubed. Another site says that granulated sugar granules are cubes of side 0.5mm. Knowing the density and the volume of them you can work out the mass. Mass = Volume x Density. Not to bore you with the maths...1 grain of sugar weighs 0.106mg (as long as I have got my conversions right). Therefore 0.018g of sugar equates to about 170 grains.

Comments

Popular posts from this blog

The CCG Project!

In order to find out the situation around the country for Libre prescribing now that the national policy has been published, I have made the decision to contact many of them to find out their plans.  I have arbitrarily chosen to contact all English CCGs that in December 2018 prescribed Libre via Primary Care to less than 5% of their population (and one specific request from a group member).  I had hoped this would be a small list, but there are 135 CCGs on the list.  I may have bitten off more than I can chew, but I'm committed to doing this and feeding back.  It worked before and hopefully this level of scrutiny will bring similar results. Below is a screenshot of the base document I am sending to each of the CCGs - it has some fields that are merge fields, so don't worry about the brackets and codes in the document (I found a typo, which has now been corrected too) .  The major piece of work with respect to this is finding the right person to contact.  However, I have s

Abbott dX 2022 Barcelona - "Make it Count"

For the past four years I've been invited by Abbott to a conference bringing together people with diabetes from across Europe to discuss various topics.  The first year I was meant to attend, it was my 'man v horse' year (the horse won!), so was unable to attend and then the pandemic hit so two further dX's were held virtually.  I was fortunate to be asked to present at last year's session.  This year's event was back in-person and held in Barcelona, coinciding with the latter part of the ATTD conference.   At this point, I must make it very clear - Abbott invited me to the 2022 European Diabetes Exchange forum (dX), that took place in Barcelona.  I attended this two-day event to connect and interact with inspirational and influential people in the diabetes community.  Abbott paid for my ticket and accommodation. #InvitedbyAbbott.  This is formal and it needs to be - I have not been required to do anything by Abbott as a result of my attendance and I hope that m

Finally an Update!

So, I have finally got the motivation to update my blog. There's probably nobody reading it anymore, but just in case...here goes. What has been happening? Well, I am still honeymooning in terms of my diabetes, so need less insulin than previously. It is proving a bit difficult to judge and I had a bad hypo last week. Basically, I was almost unconscious and Claire had gone out for the evening! Luckily I found some wine gums and came out of it eventually. Last weekend was Josh's thanksgiving. Our church doesn't really approve of christenings of babies whose parents are not both confirmed. As neither of us are, then a thanksgiving was the choice. It turned out to be a lovely service and the small group of people that we had meant that it was a great day. The sun even shone for most of it. This weekend is the Open Day at work. I have helped organise it, including getting a person to create a special newspaper for the day and be there to add pictures and make a live n