Comparison of ELISA and TLC Methods for the Morphine Detection in Urine of Drug Abusers

The current study was conducted to compare ELISA with thin layer chromatography (TLC) methods for diagnosis of morphine in the urine.
Positive urine samples for morphine confirmed by immunochromatographic strips were collected from the Imam Reza Toxicology Laboratory, Mashhad University of Medical Sciences, Mashhad, Iran in 2012 for the current study. Then, the collated urine samples (70) were analyzed by both ELISA and TLC methods.
On analyzing samples by TLC, 57 out of 70 (81.4%) revealed morphine spot, whereas by ELISA method all samples were positive. The difference was statisticaly significant (P=0.0001). Both immunoassays had the same 100% positive results. The possible 18.6% false positive results might be due to drug interactions. TLC is more specific but time-consuming and less sensitive than ELISA is. However, TLC is an old method but more reliable than ELISA.
Contrary to the claim that commercially available ELISA kits have a high specificity for detection of morphine derivatives; it seems that false positive results may occur. It is thus recommended that all positive results obtained from ELISA be checked by a cheap widely available confirmation test of TLC or ideally by a quantitative technique such as GC-Mass spectroscopy, particularly for legal purposes.