What are the causes of false positive and false negative of amphetamine in urine by semi quantitative immunoassay? I am using Roche analyzer for presumptive screening, what are the chances of false negative samples?
Article Performance Characteristics of Selected Immunoassays for Pre...
There is a wide variety of causes of false positives for amphetamines, therefore structural analogy as from other causes, and in the case of false negatives is interesting check the degree of cross-reactivity of the type of amphetamine with the method of immunoassay used. There is extensive literature of the subject
False positive for amphetamine may be caused by many factors including structurally related like ephedrine and unrelated compound such as ranitidine and also cross reactivity of certain compunds during immunoassays are also known culprits. Chromatography analysis will assist in ruling out suspected false positive in these immunoassays. For false negative, look out for submission of adulterated or altered specimen ( very popular among "smart" patients in the state, but are easily detected) and sometimes inappropriate cut off (sensitivity) of the anaylzer. Read the manufacturer instruction carefully
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