How accurate are drug screening kits which you can perform yourself?

The general range of accuracy is about 95%, which is considered quite good. All drug screening kits have received approval from the FDA. To gain FDA approval, the manufacturer must demonstrate through their own clinical trials that their drug kits work adequately. All manufacturers of screening kits state that positive results from their kits should be confirmed by a laboratory, preferably with GAS Chromatography/Mass Spectrometry (GC/MS).