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

The mean of GFR-estimates based on serum creatinine (eGFR) and cystatin C (eGFR) has superior accuracy than each estimate alone. Recent studies have shown that agreement between eGFR and eGFR is an indicator for the accuracy of the mean of the two estimates. As long as the difference between the two (|ΔeGFR|) is below 40%, a high P accuracy rate of more than 90% was documented in research settings using gold-standard GFR measurements. This was the case in approximately 80% of the measurements. The study was set out to explore |eGFR| in a broader pediatric nephrological population and identify factors influencing the discrepancy between eGFR and eGFR. We retrospectively analyzed 1596 simultaneous cystatin C and creatinine measurements in 649 unique patients at the pediatric nephrology outpatient clinic of VU university medical center. The FASage equation was used to calculate eGFR, FAScys for eGFR. |ΔeGFR| was calculated as 100x(|eGFR-eGFR|)/(0.5x(eGFR+eGFR). ΔeGFR below 40% was considered high agreement. Patient characteristics like age, diagnosis, glucocorticosteroid use, eGFR, BMI and sex were analyzed for their effect on ΔeGFR below or above 40% using non-parametric tests and a potential explanation for measurements with low agreement was sought. Eighty-seven percent of the population had a |ΔeGFR| lower than 40%. Measurements with |ΔeGFR| above 40% were significantly more frequent from patients with neural tube defects. In 102 out of 208 measurements with low agreement, a potential explanation was found. In a broad pediatric nephrological population, |ΔeGFR| is below 40% in the vast majority of measurements. In this group, the mean of eGFR and eGFR can be used as an accurate estimate of GFR.