RT Journal Article
SR Electronic
T1 Confirmation and certainty in toxicology screening.
JF Clinical Chemistry
JO Clin. Chem.
FD American Association for Clinical Chemistry
SP 1535
OP 1539
VO 34
IS 8
A1 Spiehler, V R
A1 O'Donnell, C M
A1 Gokhale, D V
YR 1988
UL http://clinchem.aaccjnls.org/content/34/8/1535.abstract
AB Confirmation of presumptive positive urine drug screens, necessary to minimize the reporting of false-positive results, can be costly and time-consuming. The predictive value model can be used to select the confirming tests and to calculate the confidence of the result. The predictive value of a test result is the probability, based on the sensitivity and specificity of the test, that the result is a true positive or a true negative. The predictive value model applied to toxicology screening tests for drugs of abuse showed that prevalence, in addition to sensitivity and specificity, was the factor controlling the confidence level of a result. For example, the predictive value of a positive result for a screening test that has a sensitivity of 99% and a specificity of 99%, applied to screening in a population with a prevalence of 1% is 0.50; for a prevalence of 10%, it is 0.92. Confirmation with a second, chemically independent, test of equal sensitivity and specificity increases the predictive value to 0.99.