Blood Sugar Unit Conversion



When traveling in other countries, it would be wise to know how the blood sugar units are presented there, and be able to do a blood sugar unit conversion. Especially, if you have to use the diabetic supplies what is locally available, or if you need medical assistance during your visit abroad.

The measurement for blood sugar is generally expressed in two ways;  mg/dL or mmol/L. In the United States, Germany and other countries, the blood-sugar unit is mg/dL (milligrams per deciliter). The international standard method of measuring blood-glucose level is in mmol/L (millimoles per liter). 

Millimoles per liter (mmol/L) expresses molar concentration, also called molarity. It is the measurement of the concentration of glucose in the blood plasma. A mole is an amount of a substance that contains a large number (6.022*10^23) of molecules. A millimole is one-thousandth of a mole. A liter is the volume measurement of a liquid.

The scientific journals are all moving toward using mmol/L exclusively. However, mg/dL won't disappear soon, as some journals now use mmol/L as the primary unit and quote mg/dL in parentheses, reflecting the large base of researchers, health care providers and diabetics who are already familiar with mg/dL.

Milligrams per deciliter (mg/dL) measures the mass (mg) of glucose in the blood plasma (dL). A milligram is one-thousandth of a of a gram. A deciliter is a unit of volume, defined as one-tenth of a liter.

 

Switching between the two scales

There are two main methods of describing concentrations; by weight, and by molecular count. Weights are in grams, molecular counts in moles. The concentration is always "per" some volume, often a liter. This means that the conversion factor depends on the molecular weight of the substance in question.

To convert molar measurements to mass, the molecular weight (mass) must be established. The molecular weight of glucose (C6H12O6) is 180. In measuring glucose the difference between the two scales is a factor of 18 (liter / 10 = deciliter). Thus, 1 mmol/L is equal to 18 mg/dL.

To express mmol/L as mg/dL the measurement must be multiplied by 18 and to show mg/dL as mmol/L divide by 18. i.e. mmol/L * 18 = mg/dL and mg/dL / 18 = mmol/L

Many meters now have a switch that allows you to change between units. Either a physical switch or with an option that you can set. You could easily be misled by the unit on display, seeing a reading in mmol/L and thinking it is a very low mg/dL, or the converse. The thing to remember is that if the number have a decimal point, it usually is in mmol/L and without a decimal point, it is most likely mg/dL. When your meter presents an unusually high or low number, check the unit setting before taking any drastic action.  

The measurements we normally deal with are approximations at best of times, because reflectance meters have some error margin due to environmental factors and inherent limitations. Furthermore, plasma readings are 15% higher than whole blood. Nowadays, most meters are calibrated to give plasma readings. Capillary blood is slower to show fast changing blood-glucose levels than venous blood, as after a meal.

There would be no real harm to round off to make the values easier to comprehend. To calculate up to the hundredths place just add to the confusion and is not that influential in the result. For example, 120 mg/dL converts to 6, 666... mmol/L but 6,6 or 6,7 would be reasonably correct. Similarly, 4,7 mmol/L converts to 84,6 mg/dL, which can be quoted as 84 or 85, still conveying an acceptable value.


Table for Blood Sugar Unit Conversion

Using a table might be more convenient to do blood sugar unit conversion,  than the raw conversion factor, since we usually talk in approximations anyway.

 

Blood Sugar Unit conversion table



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