I have a borderline serum blood test (.09). I need to convert it to Whole blood equivalent. I know there are some "general" conversions ranging from 8% - 25% lower. If I know the defendant's hematacrit percentage, is there a more accurate/specific conversion that can be used?

It has been well established that substantial differences exist in ethanol content between serum and whole blood. This is due to the fact that ethanol distributes within the aqueous fraction of body tissues. Whole blood contains blood cells, lipids, and proteins, and has a water content of approximately 86%. Removal of the cells yields plasma, and further elimination of proteinaceous clotting factors yields serum. The water content of both plasma and serum is approximately 98%. Because of this higher percentage, ethanol levels will be higher in these fractions than in whole blood. The ratio of ethanol in serum to ethanol in whole blood ranges from 1.09:1 to 1.18:1, indicating that ethanol levels will be 9-18% higher in serum.

It has been established that reducing serum ethanol concentrations by 15-18% is a valid method for calculating whole blood ethanol levels. We recommend a value of 20%, which is at the upper limit of what has been reported by investigators to be the average serum: whole blood ethanol ratio, and thus should be valid for essentially all individuals. The higher percentage is favorable to the defendant, returning a lower blood ethanol concentration and precluding legal challenges that serum ethanol results overstate corresponding whole blood values.

Therefore, when converting between serum and whole blood ethanol concentrations, we recommend using the following formulas:

serum ethanol x 0.8 = whole blood ethanol

whole blood ethanol/0.8 = serum ethanol

I've seen the 15-18% range. However, with an .09 serum test about 2 hours after the accident, I need to minimize any "estimates". I have the Hematacrit percentage which gives me the specific individual's percentage of whole blood that is made up of cellular material. What I�m wondering is can I use this percentage to get an exact or near exact comparison to a whole blood result. Then all I have to deal with is a couple of hours of reverse extrapolation.

I have dealt with this issue in a number of cases and the formula for conversion that my experts have used is to divide the hospital serum result by 1.16 which gives you about a .077. (Said formula can be found on page 57 of TDCAA publication "DWI Investigation and Prosecution")If you have further questions feel free to call me. (817) 884 1649.

And that is a great book for any DWI question. Richard just finished a tough prosecution of a DWI manslaughter, involving the death of a police officer. The defendant had many excuses, none of which were accepted by the jury. Congratulations on the good work.

Now for the stupid question.....How do you know if the test you are holding is a serum or whole blood test?
Most of our blood tests are conducted through the DPS lab in Midland and I routinely get boderline (.08-.09) results. I noticed "the book" said most forensic labs use whole blood....does that include DPS? Thanks for the help.

Hospitals almost always do serum blood test. In this case, I called and double checked to confirm it was a serum test. DPS does a whole blood blood test. I also have a DPS test but it was almost 4 hours after the accident at an .02

What a great and helpful thread! You CAN teach an old dog new tricks!

I have a spreadsheet that I did using three different serum to whole blood ratios based on a high, average, and low ratio. You put in your number (mg/DL) and it gives you a BAC for all three. I would be happy to send it to you. email me at Johnf.Lopez@co.travis.tx.us.