A person’s blood alcohol content is constantly changing depending on the rate of alcohol absorption and elimination.

Alfonso Gambone
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A Philadelphia criminal defense attorney representing accused persons throughout Pennsylvania and New Jersey.

Our law firm defends DUI/DWI offenses in Pennsylvania and New Jersey and these criminal offenses often involve the introduction of evidence regarding a suspect’s blood alcohol content (BAC). If your case is proceeding to trial, it is important that your defense attorney identifies any issues with the blood evidence as this is a critical element in most DUI charges, and specifically, the more serious charges which require the Commonwealth to prove a specific BAC beyond a reasonable doubt. In Pennsylvania there are actually 9 types of DUI charges and I encourage you to read my previous article on this for more information. 


What DUI Blood Test Don’t Measure 


This may shock a lot of readers but DUI blood tests measure BAC but don’t measure BAC at the time of driving. This is important because Section 3802 b & c (Title 75) require that the Commonwealth prove a specific BAC level within 2 hours after a person has driven or was in actual physical control of the vehicle. If the Commonwealth can’t prove this element of this criminal charge, beyond a reasonable doubt, a judge or jury will have to find the person not guilty. 


In most situations a blood test is administered at least 30 minutes after an accused person has driven a car. A person’s blood alcohol content is constantly changing depending on the rate of alcohol absorption and elimination. Because BAC is constantly in flux, it is possible to show that a person was under the legal limit even though test results revealed a BAC of .08 or higher according to the test. This is also known as the “rising alcohol defense”. When you drink alcohol, your BAC gradually rises as alcohol is absorbed and reaches a peak whereupon it begins to fall as alcohol is metabolized into your system. 


Factors Which Cause BAC to Rise...and then fall  


If a person’s BAC was rising when he or she was arrested, the test results would actually be higher than when they were driving. The time it takes for someone’s BAC to reach peak absorption depends on the following factors: 


The person’s weight and body composition 


Quantity of alcohol 


Type of food eaten 

Type or proof of alcohol purchased 

Rate of drinking 

Medications and drugs 


The closer in time of a blood test in relation to the time when a person stops drinking is directly related to a higher rate of absorption or a rising state on the alcohol curve. Generally, the rising alcohol defense is best used when a person’ BAC is close to the legal limit and the person performs relatively well on a field sobriety test. 


Retrograde Extrapolation - Expert Testimony   


If the rising alcohol defense is raised, the prosecution may use retrograde extrapolation to meet its burden of proof. The defense can also, through its expert, introduce testimony regarding retrograde extrapolation but to assert this defense your attorney will need to know the following: 


  • The time you started drinking 

  • How much you had to drink  

  • Time you began to drive 

  • Time that you were stopped 


For more information on the rising alcohol defense please keep reading this blog and visit my free download section. 

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