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Serum cystatin C is not a better marker of creatinine or digoxin clearance than serum creatinine
Author(s) -
O'Riordan S.,
Ouldred E.,
Brice S.,
Jackson S. H. D.,
Swift C. G.
Publication year - 2002
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1046/j.1365-2125.2002.01549.x
Subject(s) - creatinine , digoxin , renal function , cystatin c , medicine , pharmacokinetics , endocrinology , urology , heart failure
Aims To assess whether cystatin C, a new serum marker of renal function, is a better index of creatinine or digoxin clearance than serum creatinine in older people. Methods Twenty‐two volunteers over the age of 65 years (mean 73±5) were recruited from a healthy elderly volunteer database. None of the volunteers was taking digoxin or other medication known to interfere with digoxin kinetics or assay. Digoxin was infused at a dose of 7–10 µg kg −1 and blood samples were taken over the following 48 h and assayed for serum digoxin. Serum cystatin C, creatinine and creatinine clearance were measured and a calculated creatinine clearance was estimated using the Cockcroft Gault formula. Digoxin clearance was calculated using a pharmacokinetic software package. All values were log transformed to normalize their distribution. Results Of the 22 volunteers enrolled into the study, 18 completed the study. Serum cystatin C ranged between 0.72 and 1.89 mg l −1 and serum creatinine ranged from 69.6 to 153.9 µmol l −1 . Measured creatinine clearance ranged from 38 to 123 ml min −1 and calculated creatinine clearance from 29.5 to 88.0 ml min −1 . Digoxin clearance ranged from 51.0 to 103.5 ml min −1 . Cystatin C correlated extremely well with creatinine ( r =0.93, P <0.001, 95% CI 0.82, 0.97) and with creatinine clearance ( r =0.67, P =0.002, 95% CI 0.3, 0.87). Neither serum cystatin C nor serum creatinine correlated with digoxin clearance ( r =0.25, P =0.31, 95% CI −0.25, 0.64 and r =0.44, P =0.068, 95% CI −0.03, 0.75, respectively). Measured creatinine clearance, however, did correlate well with digoxin clearance ( r =0.55, P =0.018, 95% CI 0.11, 0.81). Conclusions Serum cystatin C and serum creatinine show very similar correlations with creatinine and digoxin clearances. Serum cystatin C does not offer any advantages in this respect. It remains to be seen whether cystatin C offers any advantage over creatinine in elderly people in other respects.