Is Hospital Blood-Alcohol Analysis Accurate?

Posted by Lawrence Taylor on January 25th, 2006

The problem with the intelligent discussion of legal and scientific issues when it comes to drunk driving is that there is none.  Any "discussion" is riddled with ignorance and emotion.

Let's take an example from a few days ago:

DUI Cases May Hinge on Ruling

Columbus, Ohio.  A new ruling from Ohio's Supreme Court could affect hundreds of drunk driving cases. The decision concerns where and how a suspect's blood alcohol level is tested.

"It changed the playing field," said Dan Huston of the Ohio Prosecuting Attorneys' Association. "This was a system, a process in place and that system was essentially gutted by the Supreme Court in this particular case".

The controversy is about blood taken and tested by hospitals in the most serious drunk driving accidents. Most hospitals are drawing the blood for medical testing. Their results – including blood alcohol levels – have long been used by prosecutors in court cases.  But most hospitals do not have state certification to test blood alcohol for law enforcement purposes.  So the court said those results are not admissible…

The ruling means dozens of cases already in the system are in jeopardy.

"These folks stand to walk away from these charges," Huston said describing the worst case scenario. "More likely, there will be more pleas and reductions in sentence because a chunk of evidence will be lost".

For now, prosecutors and law enforcement are taking extra steps to ensure they get admissible blood samples. But ultimately, the Ohio General Assembly may address the new legal loophole by changing the law to specify that hospital test results are acceptable for court cases.

Another damned "legal loophole", right?  And now the whole "system" is "gutted".  Or did the media maybe once again fail to investigate the facts?

The superficial fact is that the hospitals in question were simply not certified to analyze blood for alcohol.  But the real question should be: Will a blood sample analysis for alcohol concentration by a hospital give the same result as an analysis by a crime lab?

The answer: No.  The hospital analysis will show a falsely higher result.

From my book Drunk Driving Defense, 6th edition":

Blood samples obtained in drunk driving cases are generally — but not always — analyzed as whole blood (sometimes called "legal blood").  If the sample is analyzed for medical purposes, however, the test will probably be done with serum (often referred to as "medical blood").  Serum is the clear yellowish fluid obtained from separating whole blood into its solid and liquid components (usually by centrifuging the sample); the liquid portion of the blood is called plasma, which is similar to serum.  A third method involves precipitating proteins from the blood sample and centrifuging it; the result is a clear liquid called "supernatant" which is then analyzed.

Will analysis of serum/plasma or supernatant result in the same blood-alcohol readings as analysis of the whole blood?  In a study entitled "Distribution of Ethanol: Plasma to Whole Blood Ratios" (Hodgson and Shajani, 18 Forensic Science Journal 73, 1985), scientists attempted to determine the answer to this very question.  The conclusion:  Blood-alcohol concentrations in plasma were approximately 11 percent higher than that of whole blood, and those in supernatant were about 5 percent higher….

For a study that found that serum-alcohol concentration can be up to 20 percent higher than blood-alcohol concentration, see Frajola, "Blood Alcohol Testing in the Clinical laboratories: Problems and Suggested Remedies", 39(3) Clinical Chemistry 377 (1993).

 Another "legal loophole"….

  • Tox Lab Guy

    Often times we are presented with BOTH a medico-legal whole blood draw and a handful of first draws that usually include serum.  In those cases, the medico-legal draw is analyzed solo, and the others are stored for further instructions. Having to testify about hospital results isn’t usually a lot of fun due to the very reasons you mention.


    The answer: No.  The hospital analysis will show a falsely higher result.
    The hospital result isn’t falsely high, it is just reporting a different type of blood alcohol concentration (BAC).  If the hospital is reporting on serum, then its a serum BAC.  It must be understood, and every defense attorney in the country does, that per se limits are generally set for whole blood BACs.
    It’s a simple of matter of converting between the two, and the witness should give the defendant the benefit of the doubt when choosing a conversion factor.