Analytic and clinical validation of a standardized cystatin C particle enhanced turbidimetric assay (PETIA) to estimate glomerular filtration rate

Voskoboev, Nikolay V.
Larson, Timothy S.
Rule, Andrew D.
Lieske, John C.

¹Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA
²Department of Internal Medicine, Mayo Clinic, Rochester, MN, USA
³Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USA

^*Corresponding author: John C. Lieske, MD, Mayo Clinic Division of Nephrology and Hypertension, 200 First St SW, Rochester, MN 55905, USA

Phone: +1 507 2667960, Fax: +1 507 2849315, E-mail: [email protected]

Received January 31, 2012; accepted March 6, 2012; previously published online March 30, 2012

Clinical Chemistry and Laboratory Medicine 50(9):p 1591-1596, September 2012. | DOI: 10.1515/cclm-2012-0063

Abstract

Background:

Cystatin C is an alternative biomarker for assessing glomerular filtration rate (GFR), yet lack of standardization could hinder its widespread use. In this study we analytically and clinically validated a newer cystatin C particle-enhanced turbidimetric assay (PETIA) traceable to a certified reference material and compared it to the more commonly used particle-enhanced nephelometric assay (PENIA).

Methods:

Samples from four patient cohorts at the Mayo Clinic were studied: 1) clinical convenience samples (n=50); 2) samples from patients undergoing iothalamate urinary clearance testing for clinical indications (n=101); 3) volunteers without kidney disease (n=292); 4) samples from 1999 to 2000 with previous cystatin C measurements.

Results:

The cystatin C PETIA was analytically robust between 0.15 mg/L and 8.36 mg/L. PETIA cystatin C values were 27.5% higher than PENIA results. Furthermore, PENIA results were 12.9% lower in 2010 than in 2000. PETIA cystatin C values and existing equations performed reasonably well to estimate GFR with an overall -7.4% bias for all patients analyzed. Age and gender specific reference intervals were established for the PETIA cystatin C.

Conclusions:

Cystatin C can be precisely measured by PETIA traceable to the international reference material, ERM-DA471/IFCC, using a routine chemistry autoanalyzer. There are important biases between this assay and the widely employed Siemens PENIA. This study highlights the importance of assay standardization if cystatin C is to be widely used to estimate GFR.