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Estimation of Kidney Function

Estimation of Kidney Function. Richard C. Walls 07-16-2013. Importance of Kidney Function. Kidney responsible (in part/whole) for excretion of many medications from the body t 1/2 of renally cleared medications prolonged with decreasing kidney function

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Estimation of Kidney Function

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  1. Estimation of Kidney Function Richard C. Walls 07-16-2013

  2. Importance of Kidney Function • Kidney responsible (in part/whole) for excretion of many medications from the body • t1/2 of renally cleared medications prolonged with decreasing kidney function • Vancomycin: 5-11 hours w/normal function • Vancomycin: 8-10 days in ESRD • Potential for medication error • Drug accumulation & toxicity • Overly rapid clearance & subtherapeutic doses

  3. Importance of Kidney Function • Medications often require dose adjustment when eGFR < 60 • ≈40% of adults >70 years old have eGFR < 60 • This population uses 34% of all prescription drugs

  4. Estimating Kidney Function • Creatinine • Freely filtered • Minimally reabsorbed • Some secretion • Creatine Clearance estimates glomerular filtration rate • 24-hour urine collection gold standard • Time consuming • Logistically difficult

  5. Estimating Kidney Function • Equations estimating CrCl based on SCr alone desirable for convenience • Cockcroft-Gault Equation • FDA reports 1998-2007: CG equation specifically mentioned as the basis for 25% of renal adjustments for drugs reviewed • In elderly patients w/SCr < 1.0, common practice is to round SCr to 1.0 to compensate for reduced Cr production

  6. Estimating Kidney Function • Modification of Diet in Renal Disease (MDRD) • Designed and tested to more accurately estimate GFR than CG • eGFR≈ 186a* Scr-1.154* Age-0.204(*1.212 if black)(*0.742 if female) • Chronic Kidney Disease Epidemiology Study (CKD-EPI) • eGFR≈ 141 * min(,1)α* max()-1.209* 0.993Age (*1.018 if female)(*1.159 if black) • κ = 0.7 for females; 0.9 for males • α= -0.329 for females; -0.411 for males • More representative of actual GFR than MDRD in GFR > 60 • Recently National Kidney Disease Education Program has recommended eGFR equations be used interchangeably with CG for CrCl estimation

  7. Dowling Study • Objective: To evaluate how accurately different estimates of renal function reflect actual creatinine clearance. • Retrospective review of data collected as a part of the Baltimore Longitudinal Study of Aging

  8. Dowling Study • CrCl estimated/measured via • Measured 24-hour creatinine clearance (mClCr) • Cockcroft-Gault (CG) • Cockcroft-GaultSCr < 1.0 rounded to 1.0 (r-CG) • Modification of Diet in Renal Disease (MDRD) • Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) • Estimates compared for • Bias from mClCr • Variance ratio to mClCr • Dosage discordances from CG labeling

  9. Dowling Study - Population • Patients: 269 total • 140 women • 129 men • Age, yrs: 81 ± 6 • SCr: 1.1 ± 0.4 • 103 subjects < 1.0 • Avg 8.0 ± 0.1 • Race: 85% white • BMI • Only 28 patients > 30 • No patients > 40 • Overt signs of renal failure/dialysis excluded

  10. Dowling Study - Results

  11. Dowling Study - Results • Patients w/SCr < 1.0

  12. Dowling Study - Results

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