Plasma cystatin C determinations in a healthy elderly population

Plasma cystatin C measurement has been previously shown to be a better indi cator of changes in glomerular filtration rate (GFR) than plasma creatinine . The available literature on reference intervals for cystatin C concentrat ion encompasses only paediatric and adult populations up to 60 years of age , therefore we set out to determine an elderly reference range. Blood was t aken from 401 subjects (65-101 years) and cystatin C and creatinine concent rations measured using commercially available methodologies. The availabili ty of height and weight measurements allowed the additional calculation of predicted creatinine clearances using the Cockcroft and Gault formulae. Whi lst no notable gender difference in cystatin C values was observed (female, 1.48 mg/l; male, 1.53 mg/l), concentrations rose with increasing age (60-7 9 years, 1.39 mg/l; > 80 years, 1.70 mg/l). Conversely, there was a signifi cant (P < 0.0001) gender difference in creatinine values (female, 99 mu mol /l; male, 120 mu mol/l) but none between age groups (60-79 years, 105 mu mo l/l; > 80 years, 113 mu mol/l). Calculated GFR determinations resulted in a predicted creatinine clearance range of 21-81 ml/min per 1.73 m(2) (n = 36 1). There was no significant difference between gender (male, 18-88 ml/min per 1.73 m2; female, 24-69 ml/min per 1.73 m(2)), but a very significant 20 % decrease in predicted GFR per decade. Sex-related reference intervals for creatinine were established (female, 66-149 mu mol/l; male, 71-204 mu mol/ l); whilst age-related reference intervals were established for both cystat in C (60-79 years, 0.93-2.68 mg/l; > 80 years, 1.07-3.35 mg/l) and predicte d creatinine clearance (60-79 years, 27-89 ml/min per 1.73 m(2); > 80 years = 18-55 ml/min per 1.73 m(2)). Plasma cystatin C measurement offers a simp le, more sensitive screening assay for early changes in GFR and reflects th e decreasing GFR that occurs with increasing age. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.