Confirmation Testing:

Extractions and Gas Chromatography/Mass Spectrometry (GC/MS)

LabCorp performs confirmation testing using gas chromatography/mass spectrometry (GC/MS) to positively identify a drug or drug metabolite.  GC/MS is a more sensitive and specific analytical procedure.  However before donor specimens can be analyzed by GC/MS, they must be specially prepared using complex extraction procedures.

Donor specimens are scheduled for confirmation testing based on the initial test result.  These specimens are scheduled by the Laboratory Management System (LMS) into confirmation batches according to the class of drugs.  A LabCorp confirmation clerk performs a process called “bottle matching transaction”.  The clerk types identifying information from the bottle seal into the computer system.  The LMS electronically compares information from the bottle seal to the information entered from the original chain-of-custody during data entry.  The barcode number of the specimen bottle is scanned to produce an aliquot barcode that matches the original specimen barcode number.  An aliquot is removed from the original bottle and transferred to the labeled tube.  This tube is placed with other donor specimen aliquots along with calibration standard, and open and blind controls, and transferred under chain of custody to the Extraction laboratory.

This transfer, as well as all subsequent transfers, is documented on a custody and control form accompanying each batch.  Each sample is identified by the barcode label that is transferred from tube to vial throughout the process to maintain positive specimen identification throughout each step.

The Extraction department utilizes a specific procedure for each drug group.  The procedures employ either a solid-phase or a liquid-liquid extraction procedure to isolate the drug or drug metabolites from the urine.  Each batch contains a calibrator at the assay cut-off, two "open" controls (at 40% of cutoff and 125% cutoff) and two "blind" controls (one is negative and one is approximately twice the cutoff concentration).

LabCorp’s staff documents each transfer of custody on the custody and control form that accompanies the batch by indicating dates, signatures, and “reason for change”.  This document originates in the confirmation aliquot department and ends after analysis on the GC/MS.  LabCorp uses an "all-disposable" approach with glassware and devices, which come in direct contact with sample material.  Non-reusable glass tubes and caps, glass Pasteur pipettes, and plastic transfer pipettes are used exclusively for confirmation procedures.

Gas Chromatography/Mass Spectrometry (GC/MS):

Confirmation of presumptive positive specimens is performed by gas chromatography/mass spectrometry.  GC/MS provides unequivocal identification of the molecule(s) based on characteristic fragmentation patterns at specific retention times.  GC/MS is a tandem technology, utilizing a gas chromatograph coupled to a mass spectrometer.

Gas chromatography is a method of separating mixtures of analytes.  Each analyte passing through a column in the gas chromatograph has a characteristic retention time which is defined as the time from injection to peak detection.

In GC/MS, the mass spectrometer serves as the detector for the gas chromatograph.  Mass spectrometry performs the fragmentation of compounds.  The fragmentation pattern of known standards is evaluated and stored in the data processing unit of the GC/MS.  Unknown specimens are compared to the known standard.  The identification and quantification is evaluated for each control and donor specimen. GC/MS produces an unequivocal identification of a drug or drug metabolite.  The basic steps of any GC/MS analysis are as follows:

1.      Routine minor maintenance must be performed on the GC/MS before a batch can be analyzed.  This consists of an autotune, which adjusts the mass spectrometer parameters to meet predefined performance criteria.

2.      A batch of labeled vials is received along with the chain-of-custody form from the extractions department.  Samples are identified by the barcode bottle identification.

3.      A test sample is injected to ensure the instrument is performing properly.

4.      The calibration standard is injected and used to set the instrument identification and quantification parameters.  These parameters then determine the concentration in each control and specimen.

5.      The GC/MS technologist carefully monitors the batch as the instrument completes the analysis of each specimen.  After each injection, the data analysis is completed and printed at the workstation.

The GC/MS personnel conduct an initial review of the batch before releasing the batch to data review for final review and certification.  The open and blind controls must satisfy qualitative and quantitative criteria.  For a sample to be designated as positive, the concentration of drug in the sample must be greater than or equal to the cutoff, and qualitative criteria such as retention times and mass ratio must be met.