BAC stands for Blood Alcohol Concentration and BrAC for Breath Alcohol Concentration

BAC results are obtained by taking a blood sample while BrAC results are obtained by taking a breath sample. So how does it work as you may then wonder if Law Enforcement officers are using field breathalyzers to test your BrAC, but the results obtained are displayed in BAC? To put it simply, there is a chemical correlation between the alcohol content in your blood (BAC) and your breath alcohol content. BrAC results are converted to blood alcohol concentration (BAC) – we’ll explain how below.

For example, OCIGO will, accurately and reliably, measure the BrAC in your breath sample and display the BAC results on the device (not available in France) and on the APP. It’s worth noting that BAC results display will differ by European countries as they each have their own legislations framing legal limits.

To better explain the difference between BAC and BrAC, we first need to understand how the underlying physiology of how alcohol is processed by our bodies functions once it has been ingested.

How does alcohol get into your bloodstream ?

When you drink alcohol, it goes through your mouth, down your throat, and into your stomach. However, it’s neither digested nor chemically processed in your stomach. Instead, it escapes from the stomach and/or the small intestine and into your bloodstream through a process called diffusion. In other words, alcohol is absorbed through the cell membranes of your stomach and small intestine and goes directly into your blood. It is called the passive process and it happens automatically. This is why when you are drinking on an empty stomach you get intoxicated faster. Eating food helps the sobering up process.

How does alcohol get into your breath?

Once the alcohol is in your bloodstream, it is carried throughout your body through the venous system and the pumping of your heart. This includes your lungs, where some of the alcohol present in your bloodstream remains as the blood passes through and the oxygen and carbon dioxide exchange occurs. Every time you inhale and exhale, the remaining alcohol in your lungs passes back up through your throat, into your mouth, and out.

Relations between BAC and BrAC

The Relation between BAC and BrAC is determined by the Blood/Breath Ratio called BBR. The concentration of alcohol in breath is about 2.000 times less than in an equal volume of blood. It means that to compare BAC and BrAC, you need to multiply the concentration in breath by a factor, the blood-breath ratio (BBR).

BAC = BrAC x BBR

This BBR of alcohol was originally thought to be 2,100:1 when the Breathalyzer was approved for use in the USA and Canada to estimate the BAC (Borkenstein and Smith, 1961).

But, scientific articles reporting BBRs of alcohol either involve controlled drinking experiments or tests made with apprehended drivers. They show that in the vast majority of a studied population, the ratios can vary between 2.000:1 and 3.000:1.

Understanding alcohol units

BAC Units

In Europe, the metric by which BAC is measured is as follows:

  • Latin countries : g/L
  • Anglo-Saxon countries : mg/100mL
  • German and Scandinavian countries : %o[w/w] or g/kg

BrAC Units

In the Europe, the classic metric for BrAC is mg/L except for Anglo-Saxon countries (which is µg/100mL).

Calculation

To easily convert BAC to BrAC, an approximative calculation consists of dividing the BAC result by 2,000 to obtain your approximate BrAC result. In other words, if your BAC is 0.8, you may consider that your BrAC is around 0.4.

Conversion ratios used in different countries

Currently, countries are not in agreement with the BBR and unfortunately, there isn’t any scientific formula to determine the exact ratio. In Europe, BBR can vary between 2.000:1 and 2.292:1.

In conclusion, the chemical correlation between the alcohol content in your blood (BAC) and your breath alcohol content (BrAC) is not an easy topic.

Breathalyzers like OCIGO allows you to measure your level of alcohol and the OCIGO APP will help you to easily adapt BAC and BrAC levels amongst European countries.

You want to know how are breath alcohol levels mesured with infrared spectroscopy? Our article explain it all!