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COMMENTS AND OPINIONS
Vitamin D Use and Mortality in Chronic Kidney Disease: Immortal Time Bias
Wendy L. St Peter, PharmD;
Eric D. Weinhandl, MS;
Jiannong Liu, PhD
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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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RELATED ARTICLE
Association of Activated Vitamin D Treatment and Mortality in Chronic Kidney Disease
Csaba P. Kovesdy, Shahram Ahmadzadeh, John E. Anderson, and Kamyar Kalantar-Zadeh
Arch Intern Med. 2008;168(4):397-403.
ABSTRACT
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RELATED LETTER
Vitamin D Use and Mortality in Chronic Kidney Disease: Immortal Time Bias—Reply
Csaba P. Kovesdy, John E. Anderson, and Kamyar Kalantar-Zadeh
Arch Intern Med. 2008;168(21):2385-2386.
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