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Blood Test Information

The most common test used for DUI / DWI arrests is a breath test, by more than a 10 to 1 margin.  Some states (e.g., South Carolina) REQUIRE that a DUI alcohol suspect be offered a breath test, and not a blood test, if he/she is conscious.  Other states (e.g., Georgia) permit the officer in the field to choose which kind of test or tests are to be administered, whether the person is conscious or not.  Other states don’t use urine at all.  So, if you are suspected of DUI / DWI of alcohol in South Carolina, you will be offered only ONE test, and that will be breath.  In Georgia, the officer can choose ANY or ALL types of tests – blood, breath and urine.

Like most matters relating to DUI / DWI arrests, issues relating to BLOOD TESTS are controlled by state laws.  Each state typically has guidelines stating by whom and how these tests are to be taken, transported, preserved, secured, analyzed, etc.  REGULATIONS and statutes (laws) governing collecting and testing “biological specimens” (substances taken from a person’s body) will determine the proper methods in your state.  Some states (Florida) have excellent guidelines.  Others (Mississippi and Georgia) have dismal laws controlling these matters, making legal challenges by accused persons very difficult to mount.

Good DUI / DWI trial lawyers know that fighting blood tests can be easier than fighting breath tests in many cases.  Blood samples are often difficult to “track” (i.e., prove the ‘chain of custody’), and a missing link in the chain may result in acquittal, due to no admissible blood test evidence in the case.

The preferred method of blood analysis (when looking for alcohol content) is a process called “gas chromatography” or “GC”.  This testing method utilizes a measuring technique of comparison of a known “standard” to the subject’s sample.  These standards are typically certified pre-mix solutions, which have been tested and re-tested for being accurate and reliable “markers” for the GC device.

If an officer suspects that drugs are all or part of the impairing substance in your system, most states permit the officer to demand a blood sample, a urine sample, or both blood and urine.  When a crime lab checks for “drugs” (other than alcohol), a different device is used.  The internationally accepted “standard” for such testing is a “GC-MS” (gas chromatography, mass spectrophotometry) device.  This piece of equipment is capable of isolating and identifying a wide range of drugs, including prescription drugs and illegal (contraband) drugs.  It does this by matching the digitally produced “peaks” appearing on a graph-like sheet of computer paper.  The computer “tracks” the time of the introduction of the sample and the “exit” of the sample from the device and then identifies the substance based on the “retention time” (how long it took the substance to pass through a column packed with inert material).  Charts and notebooks are kept in the crime lab which tell the lab scientists how long each substance takes to “pass through” the column.  That way, once the printout of the “peaks” is finished, the laboratory chemist can compare the time of retention to the lab notebooks showing retention times for drugs or other chemicals.

Furthermore, the laboratory will usually run a quick series of “immunoassay” tests on a different device BEFORE running the time-consuming GC-MS tests.  These immunoassay tests are looking for common drugs of abuse, such as opiates, cannabinoids (marijuana), sedatives, pain killers, etc.  If these immunoassay tests come back NEGATIVE, the lab will usually report that the sample did not have any type of drugs in it.  If any class of drugs shows POSITIVE, the GC-MS will be set up to look for common drugs in that “class” (e.g., sedatives) in the blood sample.

Furthermore, some states have developed a fairly lax set of rules for blood testing, whereby testing methods other than GC and GC-MS can be used.  In most hospitals, alternative testing methods are often utilized, because they are FASTER.  Time is money in a hospital.  Plus, emergency situations call for quicker testing methods than the laborious process of setting up a proper GC or GC-MS test.  One major difference in most hospital tests is that these are often done on blood serum, not the “whole” blood. 

Any testing institution that is less reliable than your state’s crime lab is subject to legal challenge on even more grounds than those surrounding a state crime lab challenge.  A good DUI / DWI trial attorney will be well versed on these legal and scientific challenges, if such second rate, less reliable methods have been used.

Remember:  a state crime lab is operated by people.  Sometimes, people make errors.  People also change jobs and move away.  Sometimes, errors in the operation of the GC or GC-MS instruments, loss of the chain of custody documents or witnesses, or simply being unable to convince a jury of the reliability of the test results can result in an acquittal.  Don’t despair about a blood test having been taken at the time of your DUI / DWI arrest.  This may work to your advantage, if you hire a skilled DUI / DWI defense lawyer to handle your case.