Concordance between creatinine- and cystatin C-based eGFR in clinical practice

Area of Science:

• Pediatric Nephrology
• Renal Function Estimation
• Biomarker Accuracy

Background:

• The mean of estimated glomerular filtration rate (eGFR) from serum creatinine (eGFRcrea) and cystatin C (eGFRcys) offers superior accuracy compared to individual estimates.
• Agreement between eGFRcrea and eGFRcys, indicated by a low absolute difference |ΔeGFR|, is a marker for the accuracy of their combined estimate.
• Previous research established that |ΔeGFR| below 40% correlates with high accuracy (>90%) in research settings.

Purpose of the Study:

• To investigate the |ΔeGFR| in a diverse pediatric nephrology population.
• To identify patient-specific factors influencing the discrepancy between eGFRcrea and eGFRcys.
• To assess the reliability of the mean eGFR in this population.

Main Methods:

• Retrospective analysis of 1596 simultaneous cystatin C and creatinine measurements from 649 pediatric patients.
• Calculation of eGFRcrea using the FASage equation and eGFRcys using the FAScys equation.
• Determination of |ΔeGFR| using the formula: 100x(|eGFRcrea-eGFRcys|)/(0.5x(eGFRcrea+eGFRcys)). Analysis of patient characteristics (age, diagnosis, medication, BMI, sex) for their impact on |ΔeGFR|.

Main Results:

• A majority of the pediatric population (87%) exhibited a |ΔeGFR| below 40%, indicating high agreement.
• Measurements with |ΔeGFR| above 40% were significantly more prevalent in patients with neural tube defects.
• A potential explanation for low agreement was identified in 102 out of 208 measurements.

Conclusions:

• In a broad pediatric nephrology cohort, the |ΔeGFR| is below 40% in most measurements.
• The mean of eGFRcrea and eGFRcys serves as an accurate GFR estimate when |ΔeGFR| is below 40%.
• Neural tube defects may be associated with increased discrepancy between creatinine-based and cystatin C-based eGFR.