Cystatin C-based glomerular filtration rate estimating equations in early chronic kidney disease.
OBJECTIVE
To compare performance of combined creatinine and cystatin C-based equation with equations based on either cystatin C or creatinine alone, in early chronic kidney disease.


METHODS
Diagnostic accuracy study.


METHODS
Tertiary-care hospital.


METHODS
One hundred children with chronic kidney disease who underwent 99mTc diethylenetriamine pentaacetic acid (DTPA) glomerular filtration rate measurement.


METHODS
Estimating equations for glomerular filtration rate (GFR) based on serum cystatin C alone and in combination with serum creatinine were generated using regression analyses. These equations and the creatinine-based equation [0.42 x height/creatinine] were validated in 42 children with glomerular filtration rate between 60 and 90 mL/min/1.73 m2. Bias, precision and accuracy of estimating equations using DTPA glomerular filtration rate as gold standard.


RESULTS
Cystatin C-based equation (GFR=96.9 - 30.4 x cystatin) overestimated while the combined cystatin C-and creatinine-based equation [GFR=11.45 x (height/creatinine) 0.356 x (1/cystatin) 0.188] underestimated the measured GFR. Cystatin C-based equation had less bias (1.9 vs. 12.4 ml/min/1.73 m2), and higher precision (13.1 vs. 25.6 mL/min/1.73 m2) and accuracy (92.1% vs. 75.7%) than creatinine-based equation. The combined cystatin C and creatinine equation had bias (-1.4 mL/min/1.73 m2) precision (15.2 mL/min/1.73 m2) and accuracy (91.2%) similar to cystatin C-based equation.


CONCLUSIONS
Cystatin C-based equation has a better performance in estimating glomerular filtration rate than creatinine-based equation in children with early chronic kidney disease. Addition of creatinine equation does not improve the performance of the cystatin C-based equation.
Departments of Pediatrics, *Cardiac Biochemistry and #Nuclear Medicine, All India Institute of Medical Sciences, Ansari Nagar, New Delhi. India. Correspondence to: Dr Pankaj Hari, Professor, Department of Pediatrics, All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110 029, India. pankajhari@hotmail.com.
Pankaj
P
Hari
Lakshmy
L
Ramakrishnan
Ruby
R
Gupta
Rakesh
R
Kumar
Arvind
A
Bagga
D002648:Child; D002675:Child, Preschool; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007677:Kidney Function Tests / Q000379:methods*; D016018:Least-Squares Analysis; D008297:Male; D051436:Renal Insufficiency, Chronic / Q000175:diagnosis* / Q000503:physiopathology*; D016284:Technetium Tc 99m Pentetate; D062606:Tertiary Care Centers
D055316:Cystatin C; D016284:Technetium Tc 99m Pentetate