Per-Ola Sundin1, Per Sjöström1, Ian Jones1, Lovisa A Olsson1, Ruzan Udumyan2, Anders Grubb3, Veronica Lindström3, Scott Montgomery2,4,5. 1. School of Medical Sciences, Örebro University, SE 701 82 Örebro, Sweden. 2. Clinical Epidemiology and Biostatistics, School of Medical Sciences, Örebro University, Örebro, Sweden. 3. Department of Clinical Chemistry, Laboratory Medicine, University Hospital, Lund, Sweden. 4. Clinical Epidemiology Unit, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden. 5. Department of Epidemiology and Public Health, University College, London, UK.
Abstract
BACKGROUND: Cystatin C may add explanatory power for associations with mortality in combination with other filtration markers, possibly indicating pathways other than glomerular filtration rate (GFR). However, this has not been firmly established since interpretation of associations independent of measured GFR (mGFR) is limited by potential multicollinearity between markers of GFR. The primary aim of this study was to assess associations between cystatin C and mortality, independent of mGFR. A secondary aim was to evaluate the utility of combining cystatin C and creatinine to predict mortality risk. METHODS: Cox regression was used to assess the associations of cystatin C and creatinine with mortality in 1157 individuals referred for assessment of plasma clearance of iohexol. RESULTS: Since cystatin C and creatinine are inversely related to mGFR, cystatin C - 1 and creatinine - 1 were used. After adjustment for mGFR, lower cystatin C - 1 (higher cystatin C concentration) and higher creatinine - 1 (lower creatinine concentration) were independently associated with increased mortality. When nested models were compared, avoiding the potential influence of multicollinearity, the independence of the associations was supported. Among models combining the markers of GFR, adjusted for demographic factors and comorbidity, cystatin C - 1 and creatinine - 1 combined explained the largest proportion of variance in associations with mortality risk ( R 2 = 0.61). Addition of mGFR did not improve the model. CONCLUSIONS: Our results suggest that both creatinine and cystatin C have independent associations with mortality not explained entirely by mGFR and that mGFR does not offer a more precise mortality risk assessment than these endogenous filtration markers combined.
BACKGROUND: Cystatin C may add explanatory power for associations with mortality in combination with other filtration markers, possibly indicating pathways other than glomerular filtration rate (GFR). However, this has not been firmly established since interpretation of associations independent of measured GFR (mGFR) is limited by potential multicollinearity between markers of GFR. The primary aim of this study was to assess associations between cystatin C and mortality, independent of mGFR. A secondary aim was to evaluate the utility of combining cystatin C and creatinine to predict mortality risk. METHODS: Cox regression was used to assess the associations of cystatin C and creatinine with mortality in 1157 individuals referred for assessment of plasma clearance of iohexol. RESULTS: Since cystatin C and creatinine are inversely related to mGFR, cystatin C - 1 and creatinine - 1 were used. After adjustment for mGFR, lower cystatin C - 1 (higher cystatin C concentration) and higher creatinine - 1 (lower creatinine concentration) were independently associated with increased mortality. When nested models were compared, avoiding the potential influence of multicollinearity, the independence of the associations was supported. Among models combining the markers of GFR, adjusted for demographic factors and comorbidity, cystatin C - 1 and creatinine - 1 combined explained the largest proportion of variance in associations with mortality risk ( R 2 = 0.61). Addition of mGFR did not improve the model. CONCLUSIONS: Our results suggest that both creatinine and cystatin C have independent associations with mortality not explained entirely by mGFR and that mGFR does not offer a more precise mortality risk assessment than these endogenous filtration markers combined.
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