DUI and Diabetes Breath and Blood Defenses
It is well known, and has been for some time, that DUI and Diabetes Breath and Blood Defenses exist. The “diabetes defense”, however, does depend highly on the facts. First, which sample are you using? Is it Blood or Breath? That does make a difference. Then if Breath, what type of instrument were you, or your client tested on? The effect of diabetes is different between IR and Fuel Cell instruments, each of which are used in breath machine testing in DUI cases.
Diabetes is a disease of the sugar processing in the body. The pancreas produces an enzyme called insulin that regulates how blood sugar gets into the body cells. In diabetics, this regulatory effect is compromised, typically by the pancreas producing too little insulin, which then has to be externally supplied, either orally or by injection (or increasingly by external pump). Diabetics can get into two types of medical emergencies, one in which the blood sugar is too low, and one in which the blood sugar is too high. Either of these can alter the level of consciousness and impair driving. Both can be life threatening, but the danger in the low blood sugar condition is more imminent.
When a diabetic can’t get enough sugar into the cells, the cells fall back on a different type of metabolism to get energy. This alternate process is also used in the Atkins style of high protein, really low carbohydrate diets, because it burns fat. This altered metabolism produces ketones, among them acetone (commonly found in nail polish remover). This process can also cause the blood pH to drop, making the blood more acidic. Hence the condition is called keto-acidosis. When this occurs, some of the acetone will be converted to isopropanol (rubbing alcohol). With nail polish remover and rubbing alcohol in their blood stream, these people tend to be fairly ill.
Properly run, a headspace Gas Chromatograph (GC) analysis of blood should be able to separate acetone and isopropanol from ethanol. Demonstrating this is the purpose of the separation matrix (the sample that contains about 5 substances along with ethanol). To be completely sure there is no other interfering substances, the blood should be run on a dual column GC.
People with high blood sugar are more prone to yeast infections, so there is always the danger of fermentation in a blood sample, and because of the higher blood sugar, the amount of ethanol that can be generated is greater. Fermentation often leaves other substances in the blood from side reactions that are markers that fermentation occurred. So extra peaks in a chromatogram is a danger sign, although there are other ways that a chromatogram can have extra peaks, so their presence is not diagnostic of fermentation. A GC cannot tell ethanol from consumption from ethanol from fermentation.
Both Acetone and Isopropanol will absorb infrared light in the same regions as ethanol, but in slightly different amounts. Modern breath testing devices are designed to detect the presence of these other substances by using the ratio of other wavelengths from the main ethanol measuring wavelength. Hence the IR systems typically have a channel around 3.38, 3.49, and 3.80. The problem is that while it is fairly easy to detect these interfering substances when they are there by themselves, it is harder to differentiate when they are there with ethanol. Different instruments have different sensitivities to these substances based on the exact choice of filter frequencies and bandwidth of the filters. Each instrument needs to have this detection system checked and validated with various mixtures of ethanol, acetone, and isopropanol to show that they are detected and not added to the ethanol result.
Fuel cell based testers are fairly immune to acetone, because acetone does not react with the catalyst in the fuel cell. The fuel cell will read isopropanol, and register an ethanol reading. Fuel cells cannot tell the difference between alcohols. There is some talk that Draeger has figured out a way to detect the presence of interfering substances based the rate of reaction in the fuel cell, that can flag an interferant. That also needs to be validated with ethanol mixtures. Keep in mind that acetone and isopropanol have different partition coefficients from ethanol, so a reading on an ethanol calibrated breath tester from one of these substances does not convert into the blood level.
Some instruments have both IR and Fuel cell detection, and if an interfering substance is present, the difference between the IR and Fuel Cell reading should indicate it. Again, the system needs to be validated using the amounts of ethanol, acetone and isopropanol that could be found in living subjects. Validation applies to the individual instrument, and not just the brand and model. The settings for these filters and ratios have to be calibrated just like the ethanol reading.
Generally, an expert cannot testify that a particular instrument IS subject to interference from acetone or isopropanol, only that the potential exists. It is up to the lab, who has access to the instrument, to demonstrate that it is not subject to that interference, because it has been specifically checked and validated with various combinations of ethanol, acetone, and isopropanol.