413, P413

Cystatin C-based GFR is more closely associated with mortality than creatinine-based GFR in unselected patients seeking health care

Johanna Helmersson-Karlqvist1,*, Johan Ärnlöv1, Anders Larsson1

1Department of Medical Sciences, Uppsala University, Uppsala, Sweden

Introduction: Clinical guidelines emphasize decreased glomerular filtration rate (GFR) as an important cardiovascular risk factor. Yet, estimated GFR (eGFR) varies depending on whether it is based on creatinine or cystatin C. A combined creatinine/cystatin C equation was recently put forward as the most accurate way to estimate GFR; however the benefits of using the combined equation for risk prediction in patients in routine clinical care is less studied.

Objectives: To compare mortality risk prediction by eGFR using the combined creatinine/cystatin C equation (CKD-EPI), a sole creatinine equation (CKD-EPI), and a sole cystatin C equation, respectively in a Swedish patient population.

Methods: Unselected patients in primary- and in-hospital care in Uppsala County, Sweden with valid cystatin C and creatinine results on the same blood sample tube (N = 13054), during 2005-2007 were included. Participants were divided into eGFR risk categories >60, 60-30 and <30 ml/min/1.73m2 by each eGFR equation. We compared mortality risks in patients who were reclassified to a higher or lower eGFR category by the combined eGFR-equation compared to the sole creatinine- or cystatin C equations, respectively.

Results: During follow-up 4398 participants died. Reduced eGFR was significanly associated with all-cause and cardiovascular death by all eGFR-equations. The net reclassification improvement (NRI) for the combined equation compared to the sole creatinine equation was 0.10 (P<0.001) for all-cause and 0.08 (P<0.001) for cardiovascular mortality, indicating improved reclassification.  In contrast, NRI for the combined equation, compared to the sole cystatin C equation, was -0.05 (P<0.001) for all-cause and -0.02 (P <0.05) for cardiovascular mortality, indicating a worsened reclassification.

Conclusion: In routine clinical care, eGFR estimated with cystatin C was more closely associated with mortality risk compared to both creatinine-based eGFR and the combined creatinine/cystatin C equation.

Keywords: Biomarker, Kidney