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Wendy L. St Peter, PharmD; Eric D. Weinhandl, MS; Jiannong Liu, PhD

	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

We are concerned that the study by Kovesdy et al,¹ showing a large positive association between mortality and activated vitamin D use in patients with chronic kidney disease, may be severely biased. Patients from a single Department of Veterans Affairs medical center were divided into an exposed group (received oral calcitriol, an activated vitamin D compound) and an unexposed group (no calcitriol). Survival analysis for the exposed group began with the date of the first calcitriol prescription. However, for the unexposed group, analysis began with the date of the first parathyroid hormone (PTH) measurement.

This inconsistency in study entry time introduced a specific lead time bias, sometimes called "immortal time bias."² Patients whose first PTH measurement predated their first calcitriol prescription could not have died. Those who died before receiving calcitriol would have been classified as unexposed. Excluding . . . [Full Text of this Article]

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