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.
Blood or protein in the urine may cause false-positive pregnancy results. Urine hCG tests may give a false-negative result if the urine is too diluted or if testing is done too soon in the pregnancy. Certain drugs such as diuretics and promethazine (an antihistamine) may cause false-negative urine results.