Reference Intervals for Kidney Function Markers in the Elderly: Standardized Cystatin C and Cystatin C based CKD-EPI eGFR Change with Nutritional Status

16.03.2012 / Nock S, Medina-Escobar P, Nydegger UE, Risch M, Risch L
Reference Intervals for Kidney Function Markers in the Elderly: Standardized Cystatin C and Cystatin C based CKD-EPI eGFR Change with Nutritional Status

Kurzbeschrieb für Probanden

Die Nierenfunktion nimmt mit dem Alter zunehmend ab. Die Frage ist nun, wann eine solche Abnahme zu viel ist, und wann nicht. Diese Arbeit ist die erste, welche für standardisierte Cystatin C- und Kreatinin-Werte sowie die davon abgeleiteten Berechnungen der Nierenfunktion Normalwerte für Senioren bestimmt hat. Zudem konnte die Arbeit zeigen, dass eine proteinreiche Ernährung unabhängig vom Alter und Geschlecht, aber nicht unabhängig von der Nierenfunktion, mit Cystatin C-Werten vergesellschaftet zu sein scheint. Die Resultate dieser Analyse wurden am nationalen Kongress für Labormedizin Swissmedlab, welcher vom 12. – 14. Juni 2012 in Bern stattgefunden hat, vorgestellt.

Kurzbeschrieb für Fachpersonen

Background:

Standardization of methods for kidney function testing as well as the preferable kidney function equations have just recently become available. Reference intervals (RI) for the different kidney function markers are ill characterized in the elderly.

Aim:

A.) To characterize RI for standardized Cystatin C (CysC); IDMS-traceable Creatinine (Cr); the CysC based CKD-EPI eGFR (eGFR-Cys) in the elderly. B.) To investigate the association between nutritional status and CysC concentrations.

Methods:

Subjectively healthy elderly individuals aged >60 yrs were enrolled included. Fasting venous blood samples were drawn. CysC was measured by PENIA (Siemens), and Cr was measured on COBAS Integra (Roche). Geriatric nutritional risk index (GNRI) was also determined. Double-sided 95% RI were assessed according to the CLSI-guideline C28-A3.

Results:

590 Men and 714 women were analyzed. Men had significantly higher Cr, CysC and eGFR-Cys (p<0.01). RI for CysC in men were: 0.66-1.17 mg/L (age 60-69), 0.63-1.36 mg/L (age 70-79), 0.66-1.77 mg/L (age >=80). RI for Cr in men were: 63-117 umol/L (age 60-69), 61-126 umol/L (age 70-79), 54-144 umol/L (age >=80). RI for eGFR-Cys in men were: 61-130 ml/min/1.73m2 (age 60-69), 46-122 ml/min/1.73m2 (age 70-79), 34-118 ml/ min/1.73m2 (age >=80). RI for CysC in women were: 0.62-1.07 mg/L (age 60-69), 0.62-1.30 mg/L (age 70-79), 0.67-1.64 mg/L (age >=80). RI for Cr in women were: 46-89 umol/L (age 60-69), 45-99 umol/L (age 70-79), 42-116 umol/L (age >=80). RI for eGFR-Cys in women were: 60-124 ml/min/1.73m2 (age 60-69), 45-119 ml/min/1.73m2 (age 70-79), 34-106 ml/min/1.73m2 (age >=80). ANOVA showed eGFR-Cys to differ according to GNRI (p<0.001): the mean eGFR-Cys was 74 ml/min/1.73m2 in the lowest GNRI tertile, and 83 ml/min/1.73m2 in the highest GNRI tertile. This association remained significant after adjustment for age and gender.

Conclusions:

Age and gender specifi c reference intervals for kidney function markers at age > 70 overlap the cut-offs used for the defi nition of chronic kidney disease. eGFR-Cys seems to be able to capture the physiologically occurring protein-induced hyperfiltration.