There are a lot of steps involved in accurately determining a persons blood alcohol concentration (BAC). Each step must be completed to properly test your blood sample. Any misstep along the testing process can result in an improper result. Most blood samples for DUI cases in Pennsylvania are tested either in a PA State Police Crime Lab or at a private lab called NMS Labs. Both use the same type of testing called gas chromatography. This method tests the unknown sample (your blood) against known samples (matrix for alcohol, marijuiana, or ther controlled substance). The known samples must be programed into the machine first before testing so the machine learns what it is looking for. The known samples must be properly prepared and tested. The unknown samples (your blood) must be stored, and prepped for testing properly.
Testing usually occurs a week or more after the samples is taken from you. A few issues that can occur during the testing process are improper storage of the sample, using the wrong sample tubes, using an improper internal standard, clotting of the blood sample, contamination, improper sample preparation, having a poorly maintained testing machine, co-elution, analytes in the blanks, retention and relative retention times being off, and many more. It is important to determine if the Labs followed all of the proper procedures and protocols to make sure the test result is accurate.