Chapter 14: False-Positive Blood Alcohol

False-Positive Blood Alcohol

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This chapter deals with several cases of false-positive blood alcohol levels. This can be due to analytical errors, interference from medication that the defendant was taking, or in the case of autopsy, the chest cavity may be contaminated by unabsorbed alcohol present in the stomach.

The enzymatic method of serum ethanol determination with alcohol dehydrogenase and NAD gave false-positive serum ethanol levels. The reason for this anomalous result of alcohol determination is given in detail in Chapter 3. To recap the principle of enzymatic alcohol determination, it can be seen that the automated analyzers utilize the following reaction:

ADH Ethylalcohol + NAD Acetaldehyde + NADH ADH = alcoholdehydrogenase; NAD = nicotinamide adenine dinucleotide

However, it became evident that the following reaction interferes and generates falsely elevated serum alcohol levels.

LDH Lactate + NAD Pyruvate + NADH

LDH = Lactate dehydrogenase

These enzymatic methods are rapid, quick, and cheaper. Again, as stated in Chapter 3, determination of alcohol by GC is the gold standard. Forensic laboratories and police toxicology laboratories use GC for ethanol determinations. In cases of automobile accidents involving severe trauma, both lactate and LDH increase and the elevated lactate does not clear rapidly (1,3-5). For this reason, a toxicologist needs to ascertain the method by which serum alcohol levels are measured.

False-positives can happen due to interference from a drug that competes with alcohol during metabolism by the liver.

False-positives may also occur during autopsy. In this case, the chest cavity blood may be contaminated with alcohol present in the stomach. In this case, the blood needs to be obtained from an alternative site and alcohol levels need to be checked in vitreous fluid (6).

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Forensic Toxicology: Medico-Legal Case Studies

14.1 Presumptive DUI, Two-Car Collision, Doctor's Death

14.1.1 Legal Aspects: Wrongful Death

This case is about a doctor's widow who brought a civil suit against the state of Arizona. The widow sought monetary compensation for the death of her husband who she believes died because of the state's negligence in failing to repair a state highway. She alleged that a Jeep driven by a teenager, Ricardo, with two other teenage passengers, lost control, entered the opposite lane, and collided head-on with the car driven by her husband. This accident happened on the state highway AR 83 at 7:45 p.m. On the other hand, the state of Arizona contends that Ricardo lost control of the Jeep he was driving because he was intoxicated.

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14.1.2 Medical Aspects

The teenage driver of the Jeep survived but suffered multiple fractures and traumas. He was transferred to Jefferson Medical Center by helicopter at approximately 8:50 p.m. The emergency room obtained his blood at 9:46 p.m. and sent it to the laboratory for toxicology analysis. The laboratory reported serum alcohol level of 162 mg/dL or 0.162%.

14.1.3 Factual Background

The doctor was driving his car home after work northbound on AR 83. At the same time, a Jeep driven by a teenager and two other teenage passengers was coming in the opposite direction, lost control, entered the opposite lane, and collided head-on with the oncoming car. The teenage driver of the Jeep, Ricardo, survived but suffered multiple fractures and traumas. Two other teenage passengers in the Jeep and the doctor driving in the other car died at the accident scene.

Ricardo is a Caucasian male, 15 years of age, and weighing 115 pounds on the day of the accident. He was transferred to Jefferson Medical Center by a helicopter at approximately 8:50 p.m. He was admitted to the emergency room with multiple fractures, head injury, shock, and coma. The patient underwent surgical procedures and was discharged after three weeks.

Since the patient was hypotensive, he received a total of 3 L of Lactated Ringer's solution en route to the hospital. A few minutes after completion of the infusion of Lactated Ringer's solution, the emergency room obtained his blood at 9:46 p.m. and sent it to the laboratory for alcohol determination. The laboratory analysis reveals several-fold elevations of liver enzymes including LDH in serum. This is not surprising due to the shock and multiple traumas the defendant experienced. The serum LDH levels were significantly elevated. The laboratory determined no lactate levels. The laboratory used

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Abbot TDx methodology for alcohol determination in serum. This method utilizes ADH enzyme. The laboratory reported serum alcohol levels of 162 mg/dL or 0.162%.

Ricardo knew that he and his friends could not legally drink as they were below the legal age to drink. They obtained beer and went to a river to swim for a few hours. Ricardo admitted drinking beer between 2:00 p.m. and 2:30 p.m. They then left the river and were going back home when the accident happened.

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14.1.4 False-Positive Blood Alcohol Levels

Because of his injuries and shock, Ricardo's blood lactate levels were expected to increase several-fold. Infusion of 3 L of Lactated Ringer's solution would further increase blood lactate considerably. Since there is no lactate utilization due to injuries, the overall blood lactate levels were expected to be extremely high at the time the blood was drawn for alcohol analysis (6,7). The laboratory analysis revealed a several-fold increase in liver enzymes including LDH.

In a normal healthy man weighing 200 pounds, one alcoholic drink is expected to give a BAC of 0.02%. Alcohol from blood is expected to dissipate at the rate of 0.02% in 1 hour (6,9). Ricardo weighed 115 pounds and admitted drinking two beers between 2:00 p.m. and 2:30 p.m. Consequently, his blood alcohol levels could go up to 0.07%. The accident occurred at approximately 7:45 p.m. There was a time lapse of approximately 5 hours from the time he drank the second beer to the time his blood was drawn. In those 5 hours, he would have eliminated any alcohol left in circulation completely. He had no alcohol in his body and was sober at the time of the accident. His serum was analyzed by the laboratory on the blood sample that was drawn at 9:46 p.m. The serum alcohol levels at this time were expected to be 0%.

The GC method of alcohol determination is the gold standard but is expensive to maintain. It has no known interferences. Several enzymatic methods by several manufacturers based on the reaction of alcohol dehydrogenase on alcohol and the conversion of NAD to NADH and extrapolating the concentration of NADH so generated to alcohol are available in the market. Several hospital laboratories use them, as they are cheaper and quicker. They are accurate in the majority of cases. But they give false-positive blood alcohol levels under certain conditions. These methods measure NADH and correlate these levels to BAC. This stoichiometric relationship is fine as long as NADH is not generated by any other enzymatic reaction. Elevated lactate and LDH in blood also generate NADH, giving false-positive blood ethanol levels (3). Several manufacturers with FDA-approved reagent kits for procedures of alcohol determination by ADH acknowledge the findings and warn about the false-positive blood alcohol levels in cases of trauma and high blood lactate and LDH levels (8).

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Forensic Toxicology: Medico-Legal Case Studies

14.1.5 Conclusions

Based on the available evidence, it can be concluded with a reasonable degree of scientific certainty that:

1. Ricardo's blood alcohol levels were falsely elevated. 2. Extremely high blood lactate and LDH levels and the use of an inap-

propriate enzymatic method utilizing ADH by Abbot TDx to measure serum alcohol resulted in false-positive alcohol levels. 3. Based on the evidence of the number of beers Ricardo drank, the period in which he drank, and the time of the accident, it can be concluded that he was sober at the time of the accident. 4. Alcohol had no role in the unfortunate accident resulting in the death of the doctor.

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14.2 Presumptive DUI and an Injured Motorcyclist

14.2.1Legal Aspects: Presumptive DUI and Injuries to a Motorcyclist

This case is about an accident involving a motorcycle driven by Mr. Skip Edwards who, while trying to avoid a collision with a car coming from the opposite direction on Circus road, went onto the shoulder of the road. He lost control, went into a ditch, received lacerations, and was bleeding profusely. At the Rexport Hospital emergency room, his serum alcohol was found to be 0.13%. He contends that he drank only three to four beers and there must be a mistake in his serum alcohol measurement by the hospital laboratory.

14.2.2Medical Aspects: Falsely Elevated Alcohol Measurements by Enzymatic Methods

The enzymatic methods use the ADH and NAD to measure serum alcohol. However, elevation of serum lactate and LDH are known to occur in patients with trauma and injuries, which interferes with enzymatic methods giving rise to falsely elevated serum alcohol levels.

14.2.3 Factual Background

Skip Edwards is a Caucasian male, 42 years of age, 5 feet 11 inches tall. He weighed 190 pounds on the day of the accident. It appears that the accident happened on a clear, sunny day at 5:30 p.m. The accident took place at a bend on Circus road. Skip and his friends were at Mr. X's bar between 4:00 p.m. and 5:00 p.m. Mr. Edwards admits drinking three to four 12-oz. beers while

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eating a chicken dinner. He and his friends proceeded on Circus road on motorcycles with the intention of going to Mrs. Edwards's workplace. Mr. Edwards's motorcycle was the middle of the three motorcycles. Ben was riding the first motorcycle, the second motorcycle behind was that of Mr. Edwards, and the motorcycle behind him was that of Jerry. The motorcycles were going north on Circus road. The motorcycle in front was approximately 10 feet in front of Mr. Edwards's motorcycle. A car driven by Mr. Josh Combs coming in the opposite lane missed the motorcycle in front and came straight at Mr. Edwards. He had very little time to act and in order to avoid the collision, he quickly drove the motorcycle to the right side of the road to avoid impact with the car. He went off the shoulder and landed on rocks in a ditch. He was bleeding profusely and sustained multiple traumas, lacerations on the tongue and face, and a fracture in the right orbital area. The accident happened at 5:30 p.m. Since Mr. Edwards was bleeding profusely, Ben drove him on his motorcycle to his wife's place of employment and from there to Mrs. Edwards's place of work. His wife took him to Rexport Hospital emergency room. He was in the hospital for two days. His urinary drug screens were negative. His blood was drawn at the hospital at 7:45 p.m. and the alcohol levels in the serum were determined by Beckman enzymatic procedure. The serum alcohol levels were found to be 0.139%. Divide by 1.18 to get a blood alcohol level of 0.12%.

14.2.4 Cars and Motorcycle Accidents

It is generally the experience of forensic pathologists and medical examiners that operators of automobiles often do not see operators of motorcycles, either because of their low profile or because they are not attuned to looking for motorcycles. Automobiles will turn in front of a motorcycle and the motorcycle will crash into the car. Most experienced operators of motorcycles assume that individuals driving cars do not see them. Motorcycles involved in accidents always eject their operator. Generally, the motorcyclist sustains either head or neck injuries. The injuries occur from being thrown from the vehicle and hitting the ground or another object (6).

With the previous evidence from forensic pathology literature, it is essential to analyze the accident carefully. The three motorcycles were going on the road one after the other. The car came in suddenly at the bend and missed the first motorcycle, which was only 10 feet away from the second motorcycle driven by Mr. Edwards. This suggests that Mr. Edwards saw the car coming at him and had a few seconds to act. He was alert and quickly went to the right side, away from the car and avoided hitting it. This suggests that his mental faculties, CNS functions, and motor skills were under his control and were not consistent with a person whose blood alcohol levels

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