BACKGROUND: Cystatin C could improve chronic kidney disease (CKD) classification 
in HIV-infected women relative to serum creatinine.
DESIGN: Retrospective cohort analysis.
METHODS: Cystatin C and creatinine were measured from specimens taken and stored 
during the 1999-2000 examination among 908 HIV-infected participants in the 
Women's Interagency HIV study (WIHS). Mean follow-up was 10.2 years. Predictors 
of differential glomerular filtration rate (GFR) estimates were evaluated with 
multivariable linear regression. The associations of baseline categories (<60, 
60-90, and >90 ml/min per 1.73 m) of creatinine estimated GFR (eGFRcr), cystatin 
C eGFR (eGFRcys), and combined creatinine-cystatin C eGFR (eGFRcr-cys) with 
all-cause mortality were evaluated using multivariable Cox regression. The net 
reclassification index (NRI) was calculated to evaluate the effect of cystatin C 
on reclassification of CKD staging.
RESULTS: CKD risk factors were associated with lower eGFRcys and eGFRcr-cys 
values compared with eGFRcr. Relative to eGFR more than 90, the eGFR less than 
60 category by eGFRcys (Adjusted hazard ratio: 2.56; 95% confidence interval: 
1.63-4.02), eGFRcr-cys (3.11; 1.94-5.00), and eGFRcr (2.34; 1.44-3.79) was 
associated with increased mortality risk. However, the eGFR 60-90 category was 
associated with increased mortality risk for eGFRcys (1.80; 1.28-2.53) and 
eGFRcr-cys (1.91; 1.38-2.66) but not eGFRcr (1.20; 0.85-1.67). The overall NRI 
for mortality was 26% when reclassifying from eGFRcr to eGFRcys (P < 0.001) and 
was 20% when reclassifying from eGFRcr to eGFRcr-cys (P < 0.001).
CONCLUSION: The addition of cystatin C may improve mortality risk prediction by 
stages of kidney function relative to creatinine. CKD risk factors are 
associated with an overestimate of GFR by serum creatinine relative to cystatin 
C.