How accurate are back calculations

[Westham92]

I posted another thread a while back about having blood taken 7 hours after my last drink. Well the officer finally got in touch yesterday and he said there was a trace of alchohol in my blood and they want to do a back calculation to when the accident actually happened. So how accurate are they. Thanks

 

[Westham92]

I posted another thread a while back about having blood taken 7 hours after my last drink. Well the officer finally got in touch yesterday and he said there was a trace of alchohol in my blood and they want to do a back calculation to when the accident actually happened. So how accurate are they. Thanks

Also what information do they need for this.

 

[Forum Moderator]

The police fill out form MGDD D when carrying out a back calculation, you will find all the information they need from you on this form.

A forensic toxicologist will carry out the back calculation. They are obviously not as accurate as blood, breath or urine samples.

The results of back calculations carried out by the police could possibly be challenged in court by employing your own forensic expert at a later date, if need be.

 

[Westham92]

The police fill out form MGDD D when carrying out a back calculation, you will find all the information they need from you on this form.

A forensic toxicologist will carry out the back calculation. They are obviously not as accurate as blood, breath or urine samples.

The results of back calculations carried out by the police could possibly be challenged in court by employing your own forensic expert at a later date, if need be.

Ok thanks for the reply the officer said "there was a trace of alcohol in your blood and you still might even be alright after the back calculation", do you think because he said that their was a minimal amount in my blood. Thanks

 

[TipsyNurse]

The police tend to put a positive slant on it to get you to co-operate with the process.

The forensic toxicologist will take information about you - most importantly your weight - and get a fair idea of what your blood alcohol level would have been after the crash. The problem you will have is that if you didn't drink anything after the accident then it is very likely you were over the limit seven hours ago - your liver will process 0.7 - 1.3 units an hour depending on your size.

If you did drink something afterwards - and hopefully mentioned it to the police - then the toxicologist will incorporate that within their calculations.

 

[Westham92]

The police tend to put a positive slant on it to get you to co-operate with the process.

The forensic toxicologist will take information about you - most importantly your weight - and get a fair idea of what your blood alcohol level would have been after the crash. The problem you will have is that if you didn't drink anything after the accident then it is very likely you were over the limit seven hours ago - your liver will process 0.7 - 1.3 units an hour depending on your size.

If you did drink something afterwards - and hopefully mentioned it to the police - then the toxicologist will incorporate that within their calculations.

Thanks for the reply I found out I had 40 milligrammes of alcohol in my blood so half the limit i couldn't recall what I eat or when I started drinking or when I stopped due to head injuries i sustained but they obviously got my height and weight. The officer said he calculates it to be really close i should find out in a couple weeks

 

[TipsyNurse]

If the seven hours were in hospital then presumably you didn't drink, which would make it almost certain you were above the limit?

I only get involved in forensic toxicology of dead people (great fun, you have to work out how much alcohol is due to decomposition ) but it is a very exact science.

 

[9019hew]

Hi, very interesting to read, recently had blood taken 8 hours after a accident and it was 60 % but having been in a coma at scene of accident and having had lots of drugs off paramedic would that make a difference does anyone no ? Thanks

 

[9019hew]

If the seven hours were in hospital then presumably you didn't drink, which would make it almost certain you were above the limit?

I only get involved in forensic toxicology of dead people (great fun, you have to work out how much alcohol is due to decomposition ) but it is a very exact science.

Hi, having a blood back calculated, do you no how you could work it out back 8 hours having not done a thing after being put in a coma and having drugs from paramedics and things will this make a difference to the results ? Thank you

 

[mrturk]

Thanks for the reply I found out I had 40 milligrammes of alcohol in my blood so half the limit i couldn't recall what I eat or when I started drinking or when I stopped due to head injuries i sustained but they obviously got my height and weight. The officer said he calculates it to be really close i should find out in a couple weeks

You said 7 hours after your last drink, but the important time is how long after you drove that the blood sample was taken? How long would that be?
Just so you're aware, for this sort of back calculation your height and weight are not used at all.

 

[mrturk]

Hi, very interesting to read, recently had blood taken 8 hours after a accident and it was 60 % but having been in a coma at scene of accident and having had lots of drugs off paramedic would that make a difference does anyone no ? Thanks

No those won't make a difference, your calculation will say you were significantly over the limit I'm afraid.

 

[9019hew]

No those won't make a difference, your calculation will say you were significantly over the limit I'm afraid.

Ok thanks, but shouldn’t they ask what weight etc you are, and do you no how much bloods change over time like per hour ? Will no more I guess in time just trying to work it out to a degree as I thought drugs they gave you and being in a coma would make a difference?

 

[mrturk]

Ok thanks, but shouldn’t they ask what weight etc you are, and do you no how much bloods change over time like per hour ? Will no more I guess in time just trying to work it out to a degree as I thought drugs they gave you and being in a coma would make a difference?

No they might interview you and ask for that information, but your height, weight and age are only used to calculate what your blood alcohol would be after drinking a certain amount of alcohol. That part is actually called a 'forward calculation'. They would use this to check if you're telling the truth about how much you drank. A back calculation doesn't use any of that, the numbers are the same for everyone. Every forensic toxicologist in the UK also uses the same numbers, as they are nationally agreed. Those are 9 mg/100mL per hour, average 19 mg/100mL per hour and max 29 mg/100mL per hour. So 8 hours after the accident with a blood level of 60 you would be back calculated to 212 mg/100mL at average alcohol metabolism, and lowest around 130, highest almost 300.

I'm afraid neither a coma nor hospital drugs would have an effect on the calculations. There are other things to consider, but from what you've described it sounds like you're looking at a conviction here.

 

[9019hew]

No they might interview you and ask for that information, but your height, weight and age are only used to calculate what your blood alcohol would be after drinking a certain amount of alcohol. That part is actually called a 'forward calculation'. They would use this to check if you're telling the truth about how much you drank. A back calculation doesn't use any of that, the numbers are the same for everyone. Every forensic toxicologist in the UK also uses the same numbers, as they are nationally agreed. Those are 9 mg/100mL per hour, average 19 mg/100mL per hour and max 29 mg/100mL per hour. So 8 hours after the accident with a blood level of 60 you would be back calculated to 212 mg/100mL at average alcohol metabolism, and lowest around 130, highest almost 300.

I'm afraid neither a coma nor hospital drugs would have an effect on the calculations. There are other things to consider, but from what you've described it sounds like you're looking at a conviction here.

Thank you, so if it was 60mg and the blood was taken 8 hours after a accident what do you think it will be? I don’t no how much your body burns a hour or things . Thanks interesting thank you

 

[thetron__]

Thank you, so if it was 60mg and the blood was taken 8 hours after a accident what do you think it will be? I don’t no how much your body burns a hour or things . Thanks interesting thank you

There is plenty of calculators online, you'll be over if it was 60 8 hours later.

 

[C J 1980]

Hi, having a blood back calculated, do you no how you could work it out back 8 hours having not done a thing after being put in a coma and having drugs from paramedics and things will this make a difference to the results ? Thank you

The paramedic will have provided a report to the police about what drugs were administered at the scene of the RTC so this makes not a blind bit of difference to any defence. The police are allowed to obtain bloods from unconscious people but they must obtain permission from the doctor who is responsible for you at hospital.

CJ