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In medicine, a gold standard test or criterion standard test is a diagnostic test or benchmark that is regarded as definitive. This can refer to diagnosing a disease process, or the criteria by which scientific evidence is evaluated. For example, in resuscitation research, the gold standard test of a medication or procedure is whether or not it leads to an increase in the number of neurologically intact survivors that walk out of the hospital.^[1] Other types of medical research might regard a significant decrease in 30 day mortality as the gold standard. The AMA Style Guide prefers the phrase Criterion Standard instead of Gold Standard, and many medical journals now mandate this usage in their instructions for contributors. For instance, Archives of Physical Medicine and Rehabilitation specifies this usage.^[2]

A hypothetical ideal gold standard test has a sensitivity, or statistical power, of 100% (it identifies all individuals with a disease process; it does not have any false-negative results) and a specificity of 100% (it does not falsely identify someone with a condition that does not have the condition; it does not have any false-positive results). In practice, there are no ideal gold standard tests.

Because tests can be incorrect (either a false-negative or a false-positive result), results should be interpreted in the context of the history, physical findings, and other test results in the individual that is being tested. It is within this context that the sensitivity and specificity of the gold standard test is determined.

Quite often the gold standard test is not the test performed in a particular individual. In fact, many gold standard tests are not performed in the clinical practice of medicine at all. This is because the gold standard test may be difficult to perform or may be impossible to perform on a living person (i.e. the test is performed as part of an autopsy), or may take too long for the results of the test to be available to be clinically useful.

As new diagnostic methods become available, the gold standard test may change over time. For instance, for the diagnosis of aortic dissection, the gold standard test used to be the aortogram, which had a sensitivity as low as 83% and a specificity as low as 87%. Since the advancements of magnetic resonance imaging, the magnetic resonance angiogram (MRA) has become the new gold standard test for aortic dissection, with a sensitivity of 95% and a specificity of 92%. Before widespread acceptance of any new test, the former test retains its status as the gold standard.