The lung cancer study was the scariest. Since cigarettes are a known lung cancer risk, it seems plausible that marijuana might carry similar risks. In fact, most of the scientific evidence tends in the opposite direction - though one would never know it from reading either the study or the Reuters wire story that got the heaviest circulation.

Conducted in New Zealand, this was what is called a "case-control" study, in which researchers looked at a group of patients who had lung cancer and compared them to a group without cancer - the controls - matched for age and other demographics. All were asked about various factors that might increase their lung cancer risk, including smoking cigarettes or marijuana. After running the data on 79 cancer cases and 324 controls through myriad equations and mathematical analyses, the researchers proclaimed that one joint packed a cancer risk roughly equal to 20 cigarettes - an assertion that became Reuters' lead.

What was downplayed in the study, published in the European Respiratory Journal, and missing entirely from most media reports was context - context that strongly suggests that its alarming conclusion is wrong.

For one thing, the new conflicts with other, much larger studies. In a study published in 1997, Kaiser-Permanente researchers followed 65,000 patients for 10 years and saw no sign of marijuana use increasing the risk of lung cancer or other smoking-related cancers. And a UCLA study similar in design to this one, published in 2006, found a trend toward lower lung cancer rates among marijuana smokers. Instead of 79 cancer cases, the UCLA team looked at 1,212. The result was so striking that they speculated that it "may reflect a protective effect of marijuana."

That's right: Marijuana might protect from cancer. Piles of published studies going back to the mid-1970s document the cancer-fighting properties of marijuana's active components, THC and other chemicals called cannabinoids. Anticancer activity has been shown in many types of malignant cells, including lung cancer cells. So even though marijuana smoke contains tars and other potentially carcinogenic compounds, it is entirely plausible that cannabinoids counter any harmful effects.

But even without such context, a closer look at the New Zealand data raises questions that should have been asked by reporters. For example, most marijuana smokers in the study actually didn't show an increased risk of cancer. The only group that did was those whose marijuana use equaled at least 10.5 "joint-years" (one joint-year equals smoking a joint every day for one year). That group constituted a whopping 14 people. All those complicated mathematical models leading to the "20 times the risk" assertion, and contradicting reams of published research, rest on exactly 14 people.

The Laboratory uses a range of carefully controlled chromatographic and immunoassay techniques for detecting and confirming the presence of drugs of abuse in urine specimens. The Laboratory aims to ensure a minimum of false 'negative' results, and that no false 'positive' results are reported. Confirmatory tests are always performed for the identification of specific amphetamine and opiate class drugs. However, in the cases of benzodiazepines, cannabis, cocaine and methadone, confirmatory tests are NOT routinely carried out, because these immunoassay are relatively specific and rarely produce false positives. Confirmatory test are, however, available for unexpected findings. The Laboratory is able to provide "absolute" confirmation of findings using gas chromatography-mass spectrometry techniques. The Laboratory participates regularly in external quality assurance schemes as part of an effort to achieve a consistently high standard of performance.

There is currently a profusion of near-patient testing devices that have been specifically targeted at drug dependency units and clinics. Some of these devices have been shown to produce accurate results. However, some devices suffer from inappropriate labeling, which together with the subjective interpretation of poorly defined reaction end-point markers, leads to misinterpretation of the results generated.

A literature search was conducted regarding the use and evaluation of near-patient testing devices for drugs-of-abuse screening. The results of this research, together our own practical evaluations of such devices, have been collated into this review.

It is proposed that although near-patient testing devices may be useful in remote areas or where rapid action needs to be taken, it should be remembered that they provide only initial screening data and may yield false-positive or flase-negative results. Such devices need to be used with caution because a rapid but unconfirmed result may lead to misdiagnosis and inappropriate treatment for those who have a drug problem. It should be noted that a single result, which may be inaccurate, could lead to the cessation of treatment and a failure to provide care for those in greatest need. In addition, false-positive results may also have medico-legal implications, especially with the initiation of the drug testing and treatment orders.

Near-patient testing devices for drugs of abuse could be an expensive and potentially inaccurate means to monitor patient treatment and drug abuse status.