ESPN 53rd Annual Meeting

ESPN 2021


 
The weighted combination of cystatin C and creatinine equations brought into practice
Tobias Oostdam 1 Emil den Bakker 1 Kajsa Åsling-Monemi 8 Ulla Berg 8 Jonas Björk 3 Karolien Goffin 2 Anders Grubb 5 Magnus Hansson 7 Karin Littmann 7 Ulf Nyman 6 Arend Bökenkamp 1

1- Emma Children’s Hospital, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
2- Department of Nuclear Medicine & Molecular Imaging, University Hospital Leuven, Katholieke Universiteit Leuven, Leuven, Belgium
3- Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden
4- Clinical Studies Sweden, Forum South, Skåne University Hospital, Lund University, Lund, Sweden
5- Department of Clinical Chemistry, Skåne University Hospital, Lund University, Lund, Sweden
6- Department of Translational Medicine, Division of Medical Radiology, Lund University, Malmö, Sweden
7- Department of Laboratory Medicine, Division of Clinical Chemistry, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden
8- Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden
 
Abstract:

Background

The mean of a creatinine-based and a cystatin C-based GFR estimation (eGFR) has higher accuracy than either of the two. If the difference between the creatinine-based and the cystatin C-based eGFR exceeds 40%, however, it has been suggested that the relative contribution of the equations should be adapted based on underlying diagnosis (“Lund approach”). In this approach, α describes the contribution of the creatinine-based eGFR, (1-α) the contribution of cystatin C.

Methods

Retrospective analysis of 1712 single plasma clearance GFR measurements from four pediatric nephrology centers. The 2 most common eGFR equation systems (i.e. Full Age Spectrum [FAS] and CKiD [bedside Schwartz-creatinine with Lyon modification in adolescent males and CKiD cystatine]) were studied. 2/3 of the cohort (mean age 11.8 years, GFR 93.8 ml/min/1.73m2) was used to determine the α-values yielding the highest P30 accuracy globally (FASα and CKiDα) as well as in diagnosis subgroups. These α-values were validated in the remaining 1/3 of the cohort. The “Lund approach” was applied to the FASα and CKiDα to assess clinical applicability.

Results

The optimal α-values were determined as 0.3 for FAS and 0.4 for CKiD. P30 accuracy for FAS0.3 and CKiD0.4 in the validation cohort was 90.2% and 91.8%, respectively. While P30 accuracy of FAS0.3 was significantly higher than FAS0.5 (90.2 vs. 87.4%, p<0.05), there was little difference between CKiD0.5 and CKiD0.4 (91.2 vs. 91.8%). The Lund approach using disease specific α-values improved accuracy slightly to 90.7% (FAS0.3) and 92.5% (CKiD0.4), respectively. This was only relevant in patients with neuromuscular diseases and spina bifida, where accuracy increased from 60 to 72% (FAS) and 56 to 72% (CKiD).

Conclusions

For calculation of the weighted mean, FAS0.3 and CKiD0.4 are the optimal mix but CKiD0.5 performs equally well. A disease-specific adaptation (i.e. 100% cystatin C eGFR) is clinically relevant only for patients with neuromuscular diseases and spina bifida.