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Kidney Week

Abstract: SA-PO159

A Non-Steady State Adaptation of the CKD-EPI Equation

Session Information

Category: Acute Kidney Injury

  • 102 AKI: Clinical, Outcomes, and Trials

Authors

  • Buchkremer, Florian, Kantonsspital Aarau, Aarau, Switzerland
  • Bock, Andreas H., Kantonsspital Aarau, Aarau, Switzerland
  • Segerer,, Stephan, Kantonsspital Aarau, Aarau, Switzerland
Background

The CKD-EPI equation is one of the most widely used estimates of kidney function. It is commonly calculated whenever a plasma creatinine (pcr) is measured, although only valid when pcr is stable. Chen proposed a “kinetic eGFR” (JASN 24, 877-888 (2013)) for non-steady state conditions. Despite its name it essentially estimates a creatinine clearance (crcl). The goal of our calculations was to develop a true kinetic eGFR estimation and to improve the underlying kinetic clearance formula by explicitly including creatinine generation rate (cgr), the creatinine distribution volume (vd), and accounting for possible changes in distribution volume (deltavd).

Methods

The pharmacokinetics of creatinine are comprehensively described by equation A. To solve it for crcl requires an iterative process, so a simplified form has been used, which we modified to allow for corrections of deltavd (equation B).
In steady state crcl is creatinine excretion rate (which equals cgr) divided by the pcr. To convert our kinetically determined crcl into CKD-EPI based eGFRs, we divided cgr by crcl and calculated a virtual steady state pcr. We then inserted this term into CKD-EPI.
Cgr and vd were estimated with published formulas (incorporating age, gender, race, weight and height). We integrated all modifications into four final kinetic CKD-EPI formulations for female and male, as well as black and non-black, respectively.

Results

The comparison of crcl values obtained by equation B and the “gold standard” equation A demonstrated excellent agreement across physiologically plausible ranges of their variables pcr1, pcr2, vd, deltavd, time interval (t) and cgr.
The final kinetic CKD-EPI equations were tested for sensitivity to deviations of cgr and vd from their estimated values. We show that differences within clinically meaningful ranges can have significant effects on the kinetic eGFR. Therefore, cgr and vd need to be checked for plausibility and adjusted (e.g. according to muscle mass, volume status) in individual patients.

Conclusion

We have developed a non-steady state adaptation of the CKD-EPI equation.

Funding

  • Private Foundation Support