[Usefulness of the formula for predicting creatinine clearance from serum cystatin C]

Estimation of Glomerular filtration rate (GFR) is crucial for the detection of renal insufficiency. In clinical practice, GFR is generally estimated from Ccr by some prediction formulas including the serum creatinine concentration and some variables: age, sex, body size. It has been suggested that serum cystatin C is less influenced by sex, body size, muscular mass or inflammation. In several studies, serum cystatin C performed better than serum creatinine did as a marker to detect GFR reduction. We developed the formula for predicting creatinine clearance (Ccr) from serum cystatin C, serum creatinine and serum beta 2-microgroburin by multiple regression analysis. In this study, we analysed 24-hour Ccr and variables (sex, age and BMI) in 82 subjects with renal diseases to develop suitable formulas. Our serum cystatin C formula is as follows: Ccr (ml/min/1.73m2) = (12.14-0.03 x age-1.72 x serum cystatin C) 2. Correlation between measured 24-hour Ccr and predicted Ccr by our serum cystatin C formula was higher (r=0.852) than our serum creatinine formula (r=0.755), serum beta 2-microgroburin formula (r=0.793), Cockcroft-Gault formula (r=0.836) and Horio formula (r=0.825). Accuracy within 15% was higher (39.0%) than other formulas (25.6-30.5%). Our formula using serum cystatin C for predicting Ccr is a useful and precise marker for Ccr than other commonly used formulas using serum creatinine.