ITEM 9.    Describe definition of and rationale for the units, cutoffs and/or categories of the results of the index tests and the reference standard.

Example

We chose three cut­off points of B type natriuretic peptide to achieve sensitivity values of at least 90%, 80%, and 70%.[1]

Test results can be truly dichotomous (e.g. present or absent), have multiple categories or be continuous. Readers need to know how the authors expressed results of the index test and reference standard. If the authors defined several categories of results, readers need to know how and when they defined category boundaries and whether they defined them prior to the study or after obtaining the results. In the latter case, there is an increased likelihood that the authors selected the cut-off value to maximize a particular test characteristic, which reduces the likelihood that another study will replicate the findings.[2,3] In the example, the authors are explicit about their selection of cut-offs for B type natriuretic peptide measurement in the diagnosis of left ventricular systolic dysfunction. They established these cut-offs post hoc to obtain specific values of sensitivity.

References