How to Convert Blood Alcohol Results to Breath Alcohol Results.
In alcohol testing, it is beneficial to understand how to convert blood alcohol results to breath alcohol results. If you work in the medical field and have anything to do with alcohol testing, you will likely encounter a laboratory alcohol test result that was performed using blood. And if you are accustomed to seeing alcohol test results performed using a breath test device, you may wonder how to relate the blood test result to the breath test result.
In the United States blood test results are typically stated in either grams of alcohol per 100 milliliters of blood (g/100 mL), or milligrams of alcohol per 100 milliliters of blood (mg/100 mL). If you are up to speed on your decimals, you know that 100 mL is the same as a deciliter (dL), so the above units of measurement can also be expressed as grams of alcohol per deciliter of blood (g/dL), or as milligrams of alcohol per deciliter of blood (mg/dL).
The unit of measurement for breath alcohol test results in the U.S. is grams of alcohol per 210 liters of breath (g/210 L).
Here is a table that shows what these numbers might look like for a blood alcohol test result of .100 g/100 ml of blood, and the corresponding result stated as a breath test result.
| Blood | Breath | ||
|---|---|---|---|
| .100 | g/100 mL | .100 | g/210 L |
| .100 | g/dL | .100 | g/210 L |
| 100 | mg/100 mL | .100 | g/210 L |
| 100 | mg/dL | .100 | g/210 L |
Note that the number is the same; the only thing that changes is the decimal.
While we expect that breath test results will be very close to blood test results, we don’t expect that they will be identical. One reason is that alcohol levels are changing all the time as an individual absorbs and eliminates alcohol, and that it would be unlikely that a blood draw and a breath test would be administered within minutes of each other. But the more important reason is that the blood/breath ratio of 1:2100, upon which the g/210 L unit of measurement is based, is more likely to understate a breath test result compared to blood.
Who were these scientists that agreed to state breath alcohol test results in terms of g/210 L, and why did they choose to understate breath test results? That’s a story for another blog post.
Sylors Chem says
Why is 0.100 g/dL of blood equal to .100 g/210L of breath where as 0.100g/100mL of blood is equal to 0.100 g/201L of breath. I’m looking at your chart and wondering why.
Jennie Lee-Pace says
Hello Sylors.
The answer is that g/dL is the same as g/100 mL. 100 mL (milliliters) = 1dL (deciliter).
Lou says
201 looks like a typo
Jack Singleton says
You are correct. The unit of measure in the first line in the table should be g/210 L, not g/201 L.
James says
I had an Alcohol (Ethanol) level of < = 4 mg/dl . I'm a bit confused as to what this would be for a breath analyzer. Can you help? I would really appreciate it…
Jack Singleton says
I assume the result of 4 mg/dL is from a blood alcohol test. Using the table in the blog post, 4 mg/dL is equal to a breath alcohol result of .004 g/210L. This would be considered to be a negligible amount of alcohol.
Natalia says
hi all,
is there any error margin associated with the measurement? If so as it would be expected with any equipment that measures something, what would that be?
Jennie Lee-Pace says
Breath alcohol instruments have what’s called an acceptable tolerance range or margin of error. That tolerance range is + or – .005 BrAC. When conducting an accuracy check on a breath alcohol device, the accuracy check results should not differ by more than ± .005 grams per 210 liters of breath from the expected value of the dry standard gas sample. If the result of the accuracy check falls outside of the acceptable tolerance range, the instrument is out of accuracy range and must be recalibrated. I hope this answers your question.
Sam says
So, does this mean that .33%GMS would be .033 BAC? Am I reading this correctly?
Jack Singleton says
I assume that .33%GMS refers to a blood test stated in grams, either .33 g/100 mL or .33 g/dL This is equivalent to .33 BAC (more precisely stated as .33 g/210L). It is not necessary to move the decimal when converting a blood test stated as g/100mL or g/dL to breath alcohol results.
Terry says
Is 0.139, (+/- 0.006 normal)?
Jack Singleton says
I assume you are referring to a blood test expressed as g/dL or g/100ml, or a breath alcohol test expressed as g/210L. A result of 0.139 significantly exceeds the 0.08 limit for drunk driving in every state, as well as the Federal limits for workplace testing of 0.040, and would not be considered to be normal. It indicates significant intoxication.
Frank says
How would you convert an Ethanol level of 172.3 (0.0-10 mg/dl) to a BrAC
Ben Train says
Hi,
i’m trying to convert two figures given to me into an equivalent breath alcohol reading please.
Two individuals had bloods taken in hospital and their blood alcohol readings were given as:
2356mg/litre and 2572mg/litre.
If you are able to tell me what this equates to in terms of Breath Alcohol reading i’d be very grateful.
Thank you
Jack Singleton says
In the U.K. blood test results are typically expressed in micrograms of alcohol per 100 milliliters of breath. Assuming a blood:breath ratio of 2000:1, a blood test result of 2356 mg/L is equivalent to a breath test result of 118 µg/100 mL. A blood test of 2572 mg/L is equivalent to a breath test result of 129 µg/100 mL. Using higher blood:breath ratios (2100:1, 2200:1, or 2300:1) will lower the corresponding breath results by about 5% for each increase in blood:breath ratio.
buu tran says
Historically, where the blood/breath ratio of 1:2100 come from?
Jack Singleton says
That’s a great question. In 1952 a subcommittee of the National Safety Council Committee on Alcohol and Other Drugs (previously called the Committee for Tests on Intoxication) reported on their study of the partition ratio between blood and breath and recommended the ratio of 1:2100. The committee wrote in 1952:
“The basic principle governing the operation of the three presently used breath test methods (the Drunkometer, the Intoximeter and the Alcometer) is the constant ratio existing between the concentration of alcohol in the alveolar air and the blood. Available information indicates that this alveolar air blood ratio is approximately 1:2100…”
(from National Safety Council, A History of the Committee on Alcohol and Other Drugs, https://www.nsc.org/Portals/0/Documents/NSCDocuments_Advocacy/NSChistoryofCAOD.pdf.)
Corey says
What is the breath alcohol content where the blood was 295 mg/dL?
Jack Singleton says
A blood alcohol test result of 295 mg/dL is equivalent to a breath alcohol result of .295 g/210L.
mike perkins says
WHAT IS THE BAC IF THE MEDICAL LAB RESULTS ID 358-HH UNITS MG/DL RANGE -80
Jack Singleton says
I am not familiar with what “HH units” refers to or with what “range -80” means. However, if this refers to a laboratory blood alcohol test result of 358 mg/DL, the corresponding breath alcohol test result is .358 BAC, or .358 g/210L.
Glenda Hurst Kennedy says
Dear Jack,
Am I correct to convert the blood test results ETHANOL 98 mg/DL to the breath test result of .098 g/210L or BAC?
Thanks,
Glenda Kennedy
Fort Lauderdale, FL
Jack Singleton says
Yes, you are correct.
William F. Kehoe, Esq. says
A Blood test results indicate “0.163% (g/100mL) = 0.004 g/100mL ethyl alcohol”
Does that equate to a 0.004 BAC?
Crystal Marchand says
What does a blood alcohol report mean when it says
Volatlies by HS-Dual GC/FID
Ethanol 0.28 grams per 100 milliliters.
If the state legal limit is .05
Yet the breath test showed a .314
What would the BAC equal to and how over the legal limit is the 0.28 grams?
Jack Singleton says
The HS-Dual GC/FID refers to the instrument used to analyze the blood sample. A blood alcohol test result of 0.28 grams per 100 milliliters (g/100 ml) is equivalent to a breath alcohol test result of 0.280 g/210L, the unit of measure for breath alcohol results used in the U.S. The blood alcohol result of 0.28 g/100ml is very close to the breath alcohol result of 0.314 g/210L. We don’t expect that the breath alcohol and the blood alcohol results will be exactly identical, only that they be reasonably close, which these results are. These results are approximately six times greater than the legal limit of 0.05.
Melissa says
What does it mean if a blood toxicology result for alcohol, quantitative is 2.0?
Jack Singleton says
I’m not sure I can accurately answer your question without knowing the units of measurement used in the blood alcohol test you ask about. My first guess was that the unit of measurement for the test about which you are inquiring was mg/Dl. But if that is the case, then 2.0 mg/Dl is equivalent to .0002 BAC which is essentially zero. That is also very likely below the limit of detection for any analyzer. Therefore, my guess of mg/Dl as the unit of measure does not seem reasonable.
Although I can’t satisfactorily answer your question about how to interpret the result, your question does illustrate how important it is to note the unit of measurement when comparing alcohol test results.
Leianna Lopez says
Hi,
Would blowing a 0.115g/210L (Breath) be considered intoxicated? And how would this compare to the legal limit (0.08)?
Thank you
Jack Singleton says
0.115 g/210L breath alcohol result is higher than 0.080, which is the legal limit for drunk driving in every state in the U.S. You would be considered intoxicated.
Lisa Tanner says
If someones’s ethonol blood level is a 12, would that be equal to .012 compared to a breathalizer?
Jack Singleton says
Assuming that the ethanol blood level of 12 is using the unit of measure mg/dL, then you are correct that a blood ethanol of 12 mg/dL is equal to a breath test result of .012 g/210L. That is a negligible amount of alcohol.
Lionel says
All these comments don’t make sense to me, I’m in the UK and the legal limit in both the UK and the USA is 0.08 blood alcohol, and that is the equivalent to 35 in breath alcohol, so 0.16 blood alcohol and 70 breath alcohol would make you twice over the limit.
I was hoping to find out an easy way to work out how to convert blood alcohol to breath alcohol, because I like watching the USA cop drink drivers on YouTube and am interested in converting them. I’d never get in a vehicle with someone who’s only had even just one drink.