Cystatin C, mortality risk and clinical triage in US adults: threshold values and hierarchical importance.

BACKGROUND: It has been suggested that cystatin C may be a superior measure of estimated glomerular filtration rate (eGFR) than creatinine-based methods. We aimed to assess the utility of cystatin C for clinical triage in community-based settings.
METHODS: We identified cystatin C thresholds that maximize sensitivity and specificity (Max(Sn + Sp)) for predicting death and subsequently applied classification tree methodology considering serum creatinine, creatinine-based eGFR, urinary albumin-creatinine ratio and conventional modifiable risk factors to define subgroups, interactions and hierarchical ranks in fasting US adults (National Health and Nutrition Examination Survey 1988-94, followed through 2006).
RESULTS: A threshold cystatin C value of 0.94 mg/L exhibited the best maximum combined value of sensitivity and specificity for predicting death (Max(Sn + Sp), Sn 0.64/Sp 0.78). When all variables were considered jointly in a classification tree, cystatin C and albumin-creatinine ratio were the primary mortality discriminators in subgroups that added up to 41 and 14% of the study population, respectively; serum creatinine and creatinine-based eGFR were non-discriminatory.
CONCLUSION: Cystatin C may be useful for risk-based clinical triage in public health settings.