Laskey response to Solomon

We thank Dr Solomon for his constructive and insightful comments. We also agree that, from a clinical standpoint, the real “issue” is the clinical significance of contrast-induced nephropathy (CIN) (defined using the extent of change in creatinine level after exposure to contrast media). To date, the “associations” between the development of CIN and subsequent clinical events, either short-term or long-term, have been just that—associations. As such and given the impossibility of randomizing patients to CIN (the exposure), extant measures of association are likely to be confounded. Nothwithstanding this important methodological detail, the suggestion that the definition of CIN be “loosened” to include lesser degrees of change in serum creatinine level compared to the “classic” ≥0.5 mg/dL increase raises the concern regarding loss of specificity of such an approach. Unfortunately, without having a “gold standard” to refer to, the risk of introducing false-positive (smaller) increases in creatinine level remains a real, albeit unquantifiable (due to the absence of a gold standard), source of measurement bias.

We do appreciate his suggestion that our study offers the opportunity to assess the association between CIN and longer term outcomes. However, due to the unblinded, retrospective nature of such an assessment, any conclusions would necessarily be strictly qualified.

Respectfully and on behalf of my co-authors,