Schwartz formula: is one k-coefficient adequate for all children?

Area of Science:

• Pediatric Nephrology
• Clinical Chemistry
• Biostatistics

Background:

• Plasma-creatinine-based equations are standard for estimating glomerular filtration rate (eGFR).
• The 2009 Schwartz equation adapted the traditional formula for children and adolescents using a single k-coefficient.
• Previous research did not differentiate k-coefficients by age or sex in pediatric populations.

Purpose of the Study:

• To reevaluate the k-coefficient of the 2009 Schwartz equation in a pediatric population.
• To develop an improved eGFR estimation formula for children and adolescents.
• To assess the impact of age- and sex-specific coefficients on eGFR accuracy.

Main Methods:

• Linear mixed-effects models were used to reestimate the k-coefficient.
• The study included 360 French pediatric subjects (1-18 years) with 965 measurements.
• Agreement was assessed between the new Schwartz-Lyon formula, the 2009 Schwartz formula, and measured GFR (inulin clearance) in French and Swedish cohorts.

Main Results:

• The Schwartz-Lyon formula estimated k at 32.5 for boys <13 years and all girls, and 36.5 for boys ≥13 years.
• The Schwartz-Lyon formula demonstrated superior performance compared to the 2009 Schwartz formula in children <13 years.
• This improvement was evidenced by reduced overestimation of measured GFR, enhanced 10% and 30% accuracies, and a better concordance correlation coefficient.

Conclusions:

• The Schwartz formula offers a simple and effective method for routine eGFR estimation in children and adolescents.
• Implementing a specific k-coefficient for children under 13 years significantly enhances the formula's performance.
• The Schwartz-Lyon formula provides a more accurate eGFR estimation in pediatric populations.