Proteins, nucleic acids are best example of natural polymers. Similarly cellulose is also a natural polymer which acts as main structural component of plants. Usually natural polymers are composed by condensation polymerisation with the elimination of water molecule.
Drug-Laboratory Test Interactions. False-positive urine immunoassay screening tests for phencyclidine (PCP) and amphetamine have been reported in patients taking venlafaxine. This is due to lack of specificity of the screening tests. False positive test results may be expected for several days following discontinuation of venlafaxine therapy. Confirmatory tests, such as GC/MS will clear that misconception up asap...or if you are not using pcp and your dr is sceptical.
How accurate is the test? The test is fairly sensitive to the presence of drugs in the urine. This means that if drugs are present, you will usually get a preliminary positive result. If you get a preliminary positive result, you should send the urine sample to the laboratory for a second, more accurate test. It is very important to send the urine sample to the lab, because the drug of abuse urine screening may give positive results when no drugs are actually present.