The accuracy and precision of a given test are usually defined in the medical literature, and such information can be used to assess whether the results of a given test or series of tests are outside of the expected values, according to the website Lab Tests Online. However, it is important to consider a laboratory test's sensitivity and specificity when evaluating its performance.
Modern laboratory tests are designed to have the highest accuracy and precision possible, writes Lab Tests Online. While there may be variance between laboratories due to differing equipment, results should not differ greatly from one another when two labs perform tests on the same sample, nor should the results of the same test performed twice by the same lab differ more than the precision range of the test. However, differences in test results from different samples, such as from blood draws several weeks apart, are normal and expected in many cases due to changes in underlying health conditions.
In addition to accuracy and precision, the concepts of sensitivity and specificity are important to understand when evaluating the results of a specific test, as explained by Lab Tests Online. Some tests are designed to maximize sensitivity, or the chance to identify correctly true positive cases of a condition, while other tests are designed to maximize the specificity or true negative rate of the test. It is usually not possible to have a test that is both extremely sensitive and extremely specific, so the use of multiple screening tests to confirm one another is a common practice.