Attacking Blood Test Results for DWI

Attacking Blood Test Results in DWI Cases

Texas DWI Manual - Buy NowExcerpted from Texas DWI Manual

By Deandra M. Grant and Kimberly Griffin Tucker

Enzymatic assay testing is quick and inexpensive. This is the type of testing that you will typically find in a hospital lab. The process involves measuring an alcohol concentration indirectly by using the reaction of its antibody to an antigen. It is not a direct measurement of the alcohol molecule itself. Enzymatic testing is a screening test that should be confirmed using gas chromatography. However, this is generally not what occurs.

The typical case where this type of testing will be at issue involves an accident where your client was transported to the hospital, an alcohol level obtained through the hospital lab was noted in the medical records, and these records were later subpoenaed by the State to support prosecution for DWI or a related offense.

Plasma or serum, rather than whole blood, is tested using this method. Plasma results when whole blood is centrifuged (spun) and the red blood cells, white blood cells, and platelets are removed. Serum is the same as plasma minus any coagulation proteins. Measuring plasma or serum for alcohol concentration yields a measured result 16-25% higher than the alcohol concentration in whole blood. Different experts will use different conversion numbers. The range most often testified to is .13 to .20. Technical Supervisors typically use .16.

EXAMPLE: .10 serum/plasma alcohol concentration conversion to a whole blood alcohol concentration

.10 / 1.16 = .086

.10 / 1.18 = .084

.10 / 1.20 = .083

.10 / 1.25 = .080

Get the Testing Kit Insert

If you have a case where blood was drawn and tested in a hospital lab, you will need to find out what kind of testing kit was used to test the serum/plasma. It is important to obtain the insert from the enzymatic test kit. The inserts often contain language such as “not intended for forensic purposes” or something similar. They will also list substances that can interfere with the test if present at certain levels.

You will also need to obtain the Standard Operating Procedures for drawing blood at the hospital for the purposes of ethanol testing.  There will be a protocol at the hospital that emphasizes that isopropyl alcohol is not to be used to cleanse the draw site if the blood is being drawn for ethanol testing.

Make the State Produce an Expert

Prosecutors typically do not understand the difference between a forensically tested whole blood test result and a hospital lab enzymatic blood test screening. They may attempt to offer the hospital result with no conversion. Make sure you have a hearing on the issue. A blood alcohol test result refers to whole blood. Plasma or serum is merely a portion of the blood. If the State intends to offer a plasma/serum test result, you will need to argue that they should be required to have a witness capable of converting the result to a whole blood alcohol concentration; otherwise, how is a plasma or serum alcohol concentration relevant? Expert testimony is required because this is not information readily understood by the general public.

Be Alert for the Possibility of False Positives

The kits used in the hospital labs for enzymatic testing of blood plasma alcohol levels are prone to false positives. Depending on the kit used, substances in the blood such as lactic acid can cause erroneous test results.

The substance actually being measured with this type of testing is nicotinamide adenine dinucleotide (NADH). A given NADH level will tell the analyzer what the ethanol level is. However, other substances found in the blood can also convert to NADH during this same chemical reaction.

A common interferent is lactic acid which can enter the blood due to muscle or organ injury or from fluids introduced via IV. Thus, high levels of lactic acid can cause a falsely elevated ethanol result. [See Nine, J., Moraca, M., Virji, M.A. 7 Rao, N., “Serum Ethanol Determination: Comparison of Lactate and Lactate Dehydrogenase Interference in Three Enzymatic Assays,” Journal of Analytic Toxicology, 19:192-196 (1995). See also Citron, Dr. Joseph, “DUI/DWI: Hospital Laboratory Testing Lacks Forensic Reliability,” Journal of Legal Nurse Consulting, 20 (1): 3-6 (2009).]  Isopropyl alcohol is another interferent with ethanol testing via enzymatic methods.

Enzymatic Testing Case Study

The following case review provides insight into how to use these concepts in an actual trial. In this case, the hospital reported a .266 ethanol level. The jury verdict was not guilty.


Harold lost control of his truck on the ice and hit a tree. An airbag was deployed. He stumbled out of the vehicle and wandered away in the snow. Police arrived and found a great deal of blood on the airbag, in the driver’s seat, and in the snow outside the truck. A search of the area revealed footprints in the snow. An officer followed the footprints which went west, then north and then back east. Harold was eventually found huddled under a tree behind a closed car wash caked in blood. He was wet and cold and seemingly incoherent. An ambulance was called and he was transported to the hospital. No SFST’s were administered but the officers smelled alcohol.

Upon arriving at the emergency room, Harold seemingly “snapped out” of his daze and was rated a 15 on the Glasgow Coma Scale, which is a standardized method to assess brain impairment. The highest score, indicating the least impairment, is 15. An officer subsequently read Harold the DIC 24 form and requested a blood specimen. Harold refused and the officer left, despite telling him he was under arrest.

Blood was drawn approximately 30 minutes after Harold’s arrival in the emergency room (and presumably 1 ½ hours after the accident). Plasma was tested in the hospital lab using a Siemens Dimension Flex Reagent cartridge. A .266 ethanol level was reported at approximately 3:30 a.m.

A CAT scan revealed a ruptured bowel. The emergency room doctor met with Harold at 6 a.m. to discuss the injury and the needed surgery. He had Harold sign a two page medical release. Notes indicated that Harold told the doctor that he remembered drinking three to four beers. He did not remember driving or the accident. He remembered walking away from the truck and then he remembered arriving at the hospital. The doctor noted that Harold was awake, alert, and responsive.


The medical records as well as the Flex Reagent packaging insert were obtained and reviewed. The records revealed that no tests were run to determine Harold’s lactic acid level but his myoglobin level was well over 400. A normal myoglobin level does not exceed 95. Myoblogin is released into the blood when muscles are damaged and a high myoglobin count would go hand-in-hand with a high lactic acid level (also released into blood with muscle damage).

According to the packaging insert for the enzymatic test kit, lactic acid levels of 100 mg/dL and lower do NOT interfere with this particular test. However, Harold’s injuries and the myoglobin levels would indicate the likelihood of a very high lactic acid level well into the 100’s.


Police Officers—Three testified. One mentioned the large number of accidents that night due to the ice. Not one testified that Harold was intoxicated, only that he was incoherent and smelled like alcohol. Two of the officers did not know that he had emergency surgery.

Nurse—She took care of Harold the entire time he was in the emergency room which was approximately four hours. She remembered him being very stoic, and he would not let her call his family. However, when he was told the extent of his injuries, he asked her to call his mom. She obviously remembered him well and seemingly felt very sorry for him. She was never asked, nor did she testify, that he was intoxicated or that she saw any signs of intoxication.

Lab Tech—The tech who tested the blood had never testified before. He admitted that high lactic acid levels would interfere with the test and cause an elevated ethanol result.

Medical Examiner—The State brought in the County Medical Examiner to convert the serum level to a whole blood level. He used a conversion factor of .20 which lowered the .266 to a .221 (.266/1.20). He admitted that he was very familiar with gas chromatography because they use it in his lab but he was unfamiliar with enzymatic testing other than the fact that it is subject to many interfering factors. He testified that gas chromatography is the only forensically reliable testing method.

Defense Expert—The defense expert pointed out that a highly intoxicated person would not have “snapped out” of a drunken haze upon arrival at the ER. That behavior was consistent with the reaction of the central nervous system to the airbag deployment, a mild head injury, and the extreme weather. He testified that a Glasgow Coma score of 15 would not have been given to an intoxicated person. He also testified to the previously discussed information regarding myoglobin levels and lactic acid levels and the effect that would have on the testing in this case.

The lack of any notes indicating intoxication in the medical records from either the nurse or the doctor, the doctor’s description of Harold as alert, awake and responsive at 6 a.m., as well as the doctor having Harold sign his medical release for surgery were also noted. The defense expert extrapolated that if the .221 was accurate, Harold would have been somewhere around a .18 when he met with the doctor and signed the release. He noted that no surgeon would have let an intoxicated person sign his own release for emergency surgery when he could have obtained consent from Harold’s mother over the phone instead.

VERDICT: Not guilty.

About the Texas DWI Manual Authors

Deandra M. Grant focuses her practice on DWI defense in Texas.  An AV-rated attorney, she is a national instructor on DWI law and science.  She has completed coursework in DWI forensic blood and urine testing and is a trained operator and maintenance technician on the Intoxilyzer 5000. In 2017, Deandra will begin a 2 year term as President of the international DUI bar association, DUI Defense Lawyers Association.

Kimberly Griffin Tucker has practiced criminal law since 1995 and has represented hundreds of Texans charged with criminal offenses, including numerous DWI cases. She has successfully completed many training programs related to DWI defense, including the practitioner and instructor courses for the SFST certification and the overview course for the Intoxilyzer 5000.

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