"The accuracy of certified labs has never been tested. Not a single study of the accuracy of HHS certified laboratories has ever been conducted. The National Academy of Sciences and other experts have urged HHS to conduct such tests,6 but HHS has never done so. Nor has HHS allowed independent researchers to see its data. HHS’ failure to conduct or allow accuracy studies of certified labs is especially troubling in light of the federal government’s assurances that the labs it used were reliable prior to the CDC study.
"The only relevant study actually indicates that certified labs are not reliable. In 2007, the United States General Accountability Office (GAO) studied 23 labs, all of whom were federally certified. The GAO found that not one of these labs consistently followed federally mandated procedures for lab accuracy.7"
Maltby, Lewis, "Latest Research Reveals New Problems with Drug Testing," National Workrights Institute (Princeton, NJ: March 2012), p. 2.