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Compensating for the influence of total serum protein in the Schwartz formula

  • Marijn M. Speeckaert , Birgitte Wuyts , Veronique Stove , Johan Vande Walle and Joris R. Delanghe EMAIL logo
Published/Copyright: March 9, 2012

Abstract

Background: The Schwartz 2009 creatinine-based revised formula is the only pediatric GFR estimating formula, which is compatible with the recent global creatinine standardization. This formula is only applicable if enzymatic creatinine methods are used. We propose an equation, taking into account the relative bias caused by serum proteins to use Jaffe based creatinine data for GFR estimation.

Methods: In a cohort study of 100 pediatric patients, serum creatinine was measured using a kinetic rate-blanked Jaffe assay (modified kinetic alkaline picrate method), a kinetic rate-blanked Jaffe compensated assay for reactive proteins and an enzymatic assay (creatinine plus method). Serum total protein, albumin, urea, uric acid and total bilirubin were measured with the use of commercial agents.

Results: The difference in serum creatinine between the enzymatic method and the compensated Jaffe method was mainly dependent on the total protein concentration in serum (r2=0.61, p<0.001). After applying the proposed protein correction, corrected compensated Jaffe results and creatinine clearance values became interchangeable with enzymatic serum creatinine results (r2=0.99, p<0.001; Deming regression: slope: 0.9787, intercept: –0.351) and with the newly proposed Schwartz formula, respectively (r2=0.99, p<0.001; Deming regression: slope 1.004, intercept: 2.16).

Conclusions: In this study, we demonstrated the usability of the alkaline picrate method in the Schwartz formula, taking into account the relative bias caused by serum proteins.


Corresponding author: Prof. Dr. Joris R. Delanghe, Laboratory Clinical Chemistry 2P8, Ghent University Hospital, De Pintelaan 185, 9000 Ghent, Belgium Phone: +32 9 3322956, Fax: +32 9 3324985

Received: 2012-1-16
Accepted: 2012-2-17
Published Online: 2012-3-9
Published in Print: 2012-9-1

©2012 by Walter de Gruyter Berlin Boston

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