Background: The Liu Comorbidity Index uses the United States Renal Data System (USRDS) to quantify comorbidity
in chronic dialysis patients, capturing baseline comorbidities from days 91 through 270 after dialysis initiation. The
270 day survival requirement results in sample size reductions and potential survivor bias. An earlier and shorter
time-frame for data capture could be beneficial, if sufficiently similar comorbidity information could be ascertained.
Methods: USRDS data were used in a retrospective observational study of 70,114 Medicare- and Medicaid-eligible
persons who initiated chronic dialysis during the years 2000–2005. The Liu index was modified by changing the
baseline comorbidity capture period to days 1–90 after dialysis initiation for persons continuously enrolled in
Medicare. The scores resulting from the original and the modified comorbidity indices were compared, and the
impact on sample size was calculated.
Results: The original Liu comorbidity index could be calculated for 75% of the sample, but the remaining 25% did
not survive to 270 days. Among 52,937 individuals for whom both scores could be calculated, the mean scores for
the original and the modified index were 7.4 ± 4.0 and 6.4 ± 3.6 points, respectively, on a 24-point scale. The most
commonly calculated difference between scores was zero, occurring in 44% of patients. Greater comorbidity was
found in those who died before 270 days.
Conclusions: A modified version of the Liu comorbidity index captures the majority of comorbidity in persons who
are Medicare-enrolled at the time of chronic dialysis initiation. This modification reduces sample size losses and
facilitates inclusion of a sicker portion of the population in whom early mortality is common.
Keywords: Comorbidity, Kidney failure, Chronic, Renal dialysis, Epidemiologic research design
A grant from the One-University Open Access Fund at the University of Kansas was used to defray the author’s publication fees in this Open Access journal. The Open Access Fund, administered by librarians from the KU, KU Law, and KUMC libraries, is made possible by contributions from the offices of KU Provost, KU Vice Chancellor for Research & Graduate Studies, and KUMC Vice Chancellor for Research. For more information about the Open Access Fund, please see http://library.kumc.edu/authors-fund.xml.
Rigler, Sally K.; et al. (2013) Impact of a modified data capture period on Liu comorbidity index scores in Medicare enrollees initiating chronic dialysis. BMC Nephrology, 14:51. http://dx.doi.org/10.1186/1471-2369-14-51