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How to Convert Blood Alcohol Results to Breath Alcohol Results

February 18, 2016 by Jack Singleton 32 Comments

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.

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Comments

  1. Sylors Chem says

    March 13, 2017 at 2:53 pm

    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.

    Reply
    • Jennie Lee-Pace says

      March 13, 2017 at 3:58 pm

      Hello Sylors.

      The answer is that g/dL is the same as g/100 mL. 100 mL (milliliters) = 1dL (deciliter).

      Reply
  2. Lou says

    July 27, 2017 at 6:49 pm

    201 looks like a typo

    Reply
    • Jack Singleton says

      July 28, 2017 at 1:24 pm

      You are correct. The unit of measure in the first line in the table should be g/210 L, not g/201 L.

      Reply
  3. James says

    September 14, 2017 at 1:40 pm

    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…

    Reply
    • Jack Singleton says

      September 15, 2017 at 9:49 am

      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.

      Reply
  4. Natalia says

    January 8, 2018 at 9:47 am

    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?

    Reply
    • Jennie Lee-Pace says

      January 9, 2018 at 10:32 am

      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.

      Reply
  5. Sam says

    July 31, 2018 at 1:50 pm

    So, does this mean that .33%GMS would be .033 BAC? Am I reading this correctly?

    Reply
    • Jack Singleton says

      August 3, 2018 at 11:10 am

      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.

      Reply
  6. Terry says

    September 11, 2018 at 1:54 pm

    Is 0.139, (+/- 0.006 normal)?

    Reply
    • Jack Singleton says

      September 12, 2018 at 2:19 pm

      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.

      Reply
  7. Frank says

    October 28, 2019 at 8:28 pm

    How would you convert an Ethanol level of 172.3 (0.0-10 mg/dl) to a BrAC

    Reply
  8. Ben Train says

    January 7, 2020 at 6:32 am

    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

    Reply
    • Jack Singleton says

      January 8, 2020 at 3:02 pm

      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.

      Reply
  9. buu tran says

    February 25, 2020 at 11:14 am

    Historically, where the blood/breath ratio of 1:2100 come from?

    Reply
    • Jack Singleton says

      February 25, 2020 at 2:35 pm

      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.)

      Reply
  10. Corey says

    April 2, 2020 at 11:56 am

    What is the breath alcohol content where the blood was 295 mg/dL?

    Reply
    • Jack Singleton says

      April 3, 2020 at 11:11 am

      A blood alcohol test result of 295 mg/dL is equivalent to a breath alcohol result of .295 g/210L.

      Reply
  11. mike perkins says

    September 15, 2020 at 11:04 am

    WHAT IS THE BAC IF THE MEDICAL LAB RESULTS ID 358-HH UNITS MG/DL RANGE -80

    Reply
    • Jack Singleton says

      September 23, 2020 at 11:23 am

      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.

      Reply
  12. Glenda Hurst Kennedy says

    October 19, 2020 at 6:31 pm

    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

    Reply
    • Jack Singleton says

      October 20, 2020 at 12:18 pm

      Yes, you are correct.

      Reply
  13. William F. Kehoe, Esq. says

    January 27, 2021 at 8:41 am

    A Blood test results indicate “0.163% (g/100mL) = 0.004 g/100mL ethyl alcohol”
    Does that equate to a 0.004 BAC?

    Reply
  14. Crystal Marchand says

    June 11, 2021 at 4:40 pm

    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?

    Reply
    • Jack Singleton says

      June 11, 2021 at 5:15 pm

      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.

      Reply
  15. Melissa says

    September 3, 2021 at 1:42 am

    What does it mean if a blood toxicology result for alcohol, quantitative is 2.0?

    Reply
    • Jack Singleton says

      September 7, 2021 at 11:45 am

      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.

      Reply
  16. Leianna Lopez says

    May 25, 2022 at 3:02 pm

    Hi,
    Would blowing a 0.115g/210L (Breath) be considered intoxicated? And how would this compare to the legal limit (0.08)?
    Thank you

    Reply
    • Jack Singleton says

      May 25, 2022 at 5:20 pm

      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.

      Reply
  17. Lisa Tanner says

    February 16, 2023 at 10:10 pm

    If someones’s ethonol blood level is a 12, would that be equal to .012 compared to a breathalizer?

    Reply
    • Jack Singleton says

      February 17, 2023 at 11:02 am

      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.

      Reply

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