Let's say you had a drink or two but don't feel you are under the influence of alcohol. However, you are arrested on suspicion of drunk driving and offered the choice of taking a breath or blood test (or, in some states, urine). Most DUI suspects choose the breath test -- a choice which could doom your chances to prove your innocence. Consider the following advice when deciding which test to take:

1. If you smoke cigarettes, you may want to pass on that Breathalyzer mouthpiece the officer is handing you. Scientific research has shown that smoking can raise the test result considerably -- enough to get you charged and convicted of drunk driving. This is because most breath analyzing devices will falsely report acetaldehyde as alcohol. Acetaldehyde is a compound produced in the liver in small amounts as a by-product in the metabolism of alcohol. However, scientists have found acetaldehyde concentrations in the lungs of smokers are far greater than for non-smokers. ("Origin of Breath Acetaldehyde During Ethanol Oxidation: Effect of Long-Term Cigarette Smoking", 100 Journal of Laboratory Clinical Medicine 908). Translated: because breathalyzers cant tell the difference between alcohol and acetaldehyde, cigarette smokers will have a higher blood-alcohol reading.

2. If you are a diabetic with possible low blood sugar, you should also avoid the breath test. A well-documented by-product of hypoglycemia (low blood sugar) is a state called ketoacidosis, which causes the production of acetone -- and acetone, like acetaldehyde, will be reported by the Brethalyzer as alcohol. In other words, the Breathalyzer will read significant levels of alcohol on a diabetics breath where there may be little or none. See "Diabetes, Breath Acetone and Breathalyzer Accuracy: A Case Study", 9(1) Alcohol, Drugs and Driving (1993). To make matters worse, the reactions of a person in the early stages of a diabetic attack include dizziness, blurred vision, slurred speech, weakness, loss of coordination and confusion -- the same symptoms which the patrol officer is looking for: the clear signs of a person under the influence of alcohol. And the officer's observations are quickly followed by a failing performance on DUI field sobriety tests.

3. Are you on a low-carb diet? Or had nothing to eat in quite awhile? Avoid the Breathalyzer in a DUI investigation -- for the same reasons stated in number 2. Perfectly normal, healthy individuals can experience temporary conditions of low blood sugar after consuming small amounts of alcohol, resulting in exaggerated but false symptoms of intoxication. Fasting glycemia can exist where a person has not eaten in 24 hours or has been on a low-carbohydrate diet. Production of glucose in the liver is stopped while the alcohol is broken down. Result: the blood sugar level will drop, affecting the central nervous system -- and producing symptoms of a person under the influence of alcohol and a higher breath test result.

4. If you have acid reflux or have burped or belched before taking the Breathalyzer, offer to provide a blood sample instead. The reason is that you will be breathing alcohol from your stomach into your throat and oral cavity, where it will stay for 20 minutes or so -- to be breathed directly into the breath machine. This is not a good thing. The machine's computer is multiplying the amount of alcohol in the breath sample by 2100 times to provide a reading of the alcohol in the blood. This is because it assumes the sample came from the lungs, not the stomach, and the average person has 2100 units of alcohol in his blood for every unit of alcohol in his breath (called the partition ratio). The Breathalyzer does not "know" that your breath sample is not from your lungs and that it should not multiply the alcohol level by anything. Result: false high readings -- and a DUI conviction.

5. When you see that officer in the rear-view mirror, don't reach for the mouthwash or breath spray to disguise the drink or two you've had. Most of them contain significant levels of alcohol (Listerine, for example is 27% alcohol) and create a mouth alcohol effect: they remain in the oral cavity for 20 minutes or so -- just long enough to be breathed into the Breathalyzer, with the same results mentioned in number 4. Some breath machines have a mouth alcohol detector, but these are highly unreliable.