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# CKD-EPI Equations for Glomerular Filtration Rate (GFR)

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) calculator calculates the glomerular filtration rate (GFR) using serum creatinine, serum cystatin C, or both.
Equation
CKD-EPI Creatinine
CKD-EPI Cystatin C
CKD-EPI Creatinine–Cystatin C
Gender
Female
Male
Age
Y
Race
Black
Non-black
Serum creatinine
µ
Serum cystatin C
m
Result:

## Background

Measured Factor
Glomerular filtration rate (GFR)
Measured Factor Disease
• CKD
• end-stage renal disease (ESRD)
• kidney failure
• acute kidney injury
Measured Factor Detail
`The CKD-EPI calculator calculates the glomerular filtration rate (GFR) using serum creatinine, serum cystatin C, or both. GFR is a measure of kidney function and can determine stage of kidney impairment.`
Speciality
Nephrologist
Body System
Renal
Formula
The CKD-EPI equation, using serum creatinine, is GFR = 141 × [min(Scr/κ, 1)^α] × [max(Scr/κ, 1) ^( -1.209)] × (0.993^Age) × 1.018 [if female] × 1.159 [if black], where Scr is serum creatinine, κ is 0.7 for females and 0.9 for males, α is -0.329 for females and -0.411 for males, min indicates the minimum of Scr/κ or 1, and max indicates the maximum of Scr/κ or 1. The CKD-EPI equation, using serum cystatin C, is GFR = 127.7 × [CysC^(−1.17)] × [Age^(−0.13)] × 0.91 [if female] × 1.06 [if black], where CysC is serum cystatin C. The CKD-EPI equation, using serum creatinine and serum cystatin C, is GFR = = 177.6× [Scr^(−0.65)] × [CysC^(−0.57)] × [Age^(−0.20)] × 0.82 [if female] × 1.11 [if black], where Scr is serum creatinine, CysC is serum cystatin C.
Measured Factor Low Impact
• A low GFR indicates poor kidney function. A GFR of 15 <ml/min/1.73m^2 indicates kidney failure (CKD Stage V)
Measured Factor High Impact
• A GFR ≥90 ml/min/1.73m^2 indicates normal to high functioning kidneys.
Process
`Serum creatinine and serum cystatin C levels are measured by blood test.`
Preparation
• Patient should inform physician if taking drugs that may affect SCr levels such as: cimetidine, cephalosporins, certain chemotherapy drugs, NSAIDs

### Result Interpretation

Ranges Ranges
• Critical Low: A GFR of < 15 ml/min/1.73m^2 indicates kidney failure (CKD Stage V) | The patient is most likely has kidney failure and would be recommended for dialysis or transplant.
• Normal: GFR ≥90 ml/min/1.73m^2
• Normal Adult Male: GFR ≥90 ml/min/1.73m^2
• Normal Adult Female: GFR ≥90 ml/min/1.73m^2
• Normal Pediatric: 1–2 years: 105.2 ± 17.3 ml/min/1.73 m^2; 3-4 years: 111.2 ± 18.5 ml/min/1.73 m^2; 5–6 years: 114.1 ± 18.6 ml/min/1.73 m^2; 7–8 years: 111.3 ± 18.3 ml/min/1.73 m^2; 9–10 years: 110.0 ± 21.6 ml/min/1.73 m^2; 11–12 years: 116.4 ± 18.9 ml/min/1.73 m^2
• Normal Neonate Female: 1–3 days: 20.8 ± 5.0 ml/min/1.73 m^2; 3–4 days: 39.0 ± 15.1 ml/min/1.73 m^2; 4–14 days: 36.8 ± 7.2 ml/min/1.73 m^2; 6–14 days: 54.6 ± 7.6 ml/min/1.73 m^2; 15–19 days: 46.9 ± 12.5 ml/min/1.73 m^2
• Normal Geriatric Male: The GFR decreases over time with age. There is no specific normal range for the geriatric patients.
• Normal Geriatric Female: The GFR decreases over time with age. There is no specific normal range for the geriatric patients.
Result Low Conditions
• If the GFR value is lower than the lower bound of the normal range, then patient may have kidney disease, damage, or dysfunction. If the GFR stays less than 60 min/ml/1.73 m^2 for 3 months or more, then patient suffers from chronic kidney disease.
Test Limitations
`The test demographics include African Americans and Non-African Americans, limiting its use and accuracy in patients who are racial minorities. When developing the calculator, not many patients older than 70 years old were analyzed, which could limit the study's valididty in the extremely elderly population.`
References: 5

### Studies

Study Validation 1
`Inker et al. conducted their cross-sectional analysis of 13 studies to test the performance of a combined creatinine-cystain C GFR estimation. They sought to find a more exact estimate of GFR because the current methods of cystain alone or creatinine alone leads to overdiagnosis of CKD, according to the authors. They found that the combined creatinine-cystain C equation was more precise compared to the one-factor equations in estimating GFR. For example, a GFR that was measured as 45-74 ml/min/1.73m^2 based on creatinine could be further classified as above or below 60 ml/min/1.73m^2 with the combined equation. This is extremely important in accurately assessing renal function and classifying CKD. The authors concluded that this combined equation may be used as a confirmatory measure for CKD diagnosis.`
References: 6
Study Validation 2
`Hong et al. conducted their analysis to compare accuracy of CKD-EPI versus MDRD equations in patients with early CKD in order to target metabolic syndrome (MetS) in early CKD, which is essential in this population to improve outcomes and reduce cardiovascular complications. From 2009 to 2010, Hong et al. analyzed the data of 12,700 patients from the Korea National Health survey. The authors concluded that compared to the MDRD equation, the CKD-EPI equation shows better association with prevalence of MetS, particularly in the normal to mildly impaired GFR range. And, overall, CKD-EPI may improve risk stratification of individuals with MetS according to kidney function in community-based population.`
References: 7
Study Validation 3
`Moodley et al. analyzed the records of 289 South African patients from 2014 to 2016 at the Inkosi Albert Luthuli Central Hospital. The GFR of each of the patients was calculated using the MDRD equation and the race-adjusted and unadjusted CKD-EPI equations. Only black African and Indian patients were analyzed. Overall, in this patient sample, none of the equations used showed accurate eGFR within 30% of measured GFR for 90% of patients. Therefore, the equations did not meet the 2002 Kidney Disease Outcomes Quality Initiative (KDOQI) benchmark of P30 >90%, making them questionable to use in this more diverse patient population, compared to measured GFR.`
References: 8
Study Additional 2
`Machado et al. conducted a 84 patient case control study to investigate the glomerular filtration rate (GFR) estimation in type-2 diabetes (T2DM) patients. The investigators compared their sample's measured glomerular filtration rate (mGFR) to their estimated glomerular filtration rate (eGFR) using each of the following equations: Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), CKD-EPI creatinine-cystatin C (CKDEPI-CC), CKD-EPI cystatin C (CKDEPIcysC) and Caucasian Asian Pediatrics and Adults (CAPA) . The healthy group mGFR was 112±19mL/min/1.73m2 and eGFR by CKD-EPI, CKDEPI-CC, CKDEPIcysC and CAPA equations, respectively, 108±17, 102±15, 97±16 and 93±16mL/min/1.73m2. In the diabetes mellitus type II (T2DM) group, the average mGFR was 104±27 and eGFR 87±19, 80±18, 74±20 and 73±18mL/min/1.73m2, respectively. In each of the subgroups, the GFR was underestimated compared to mGFR, excepting creatinine-based CKD-EPI in the healthy group. The performance was considerably worse for GFRs above 120mL/min/1.73m2. The authors concluded that, in this study population of primarily females of both the healthy patients and T2DM patients, cystatin C-based equations, including the combined CKD-EPI creatinine-cystatin equation, failed to improve the accuracy of GFR estimation, especially for normal and high normal GFR values.`
References: 9
Study Additional 3
`Oscanoa et al. sought to compare accuracy of CKD-EPIcr (Chronic Kidney Disease Epidemiology Collaboration creatinine) and BIS1 (Berlin Initiative Study) in the elderly patient population, which herein had not been well establiched. They conducted a systematic comparative study of 16 studies dated 2009-2017, with the validity criterium being a P30 accuracy level equal to or greater than 80%. The studies were required to investigate these equations in patients over 60 years old. The investigators found that only 5 (31.3%) out of the 16 studies reporting the accuracy of the CKD-EPIcr formula met the predetermined validity criterium. Comparatively, of the 9 BIS1 studies, 6 (66.6%) met the set validity criterium. The authors'  findings suggest that the BIS1 equation may more accurately evaluate eGFR in elderly patients compared to the CKD-EPIcr equation.`
References: 10

## Authors

Andrew S. Levey, MD, is the Chief Emeritus of the Division of Nephrology and the Professor of Medicine at Tufts University School of Medicine. His research focuses on measurement and estimation of kidney function and the development of clinical practice guidelines for CKD
https://www.tuftsmedicalcenter.org/PhysicianDirectory/Andrew-Levey

## References

1. Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF 3rd, Feldman HI, et al. A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009 May 5;150(9):604-12
2. Stevens LA, Coresh J, Schmid CH, Feldman HI, Froissart M, Kusek J, et al. Estimating GFR using serum cystatin C alone and in combination with serum creatinine: a pooled analysis of 3,418 individuals with CKD. Am J Kidney Dis. 2008 Mar;51(3):395-406.
3. Schwartz GJ, Furth SL. Glomerular filtration rate measurement and estimation in chronic kidney disease. Pediatr Nephrol. 2007 Nov;22(11):1839-48. Epub 2007 Jan 10.
4. KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. URL: http://www.kdigo.org/clinical_practice_g...
5. Schold JD, et al. Implications of the CKD-EPI GFR estimation equation in clinical practice. Clin J Am Soc Nephrol. 2011 Mar;6(3):497-504.
6. Inker LA, Schmid CH, Tighiouart H, Eckfeldt JH, Feldman HI, Greene T, et al.; CKD-EPI Investigators. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012 Jul 5;367(1):20-9.
7. Hong N, Oh J, Lee YH, Youn JC, Park S, Lee SH, et al. Comparison of association of glomerular filtration rate with metabolic syndrome in a community-based population using the CKD-EPI and MDRD study equations. Clin Chim Acta. 2014 Feb 15;429:157-62.
8. Moodley N, Hariparshad S, Peer F, Gounden V. Evaluation of the CKD-EPI creatinine based glomerular filtration rate estimating equation in Black African and Indian adults in KwaZulu-Natal, South Africa. Clin Biochem. 2018 Jun 22. pii: S0009-9120(18)30521-6.
9. Machado JD, Camargo EG, Boff R, da Silva Rodrigues L, Camargo JL, Soares AA, et al.Combined creatinine-cystatin C CKD-EPI equation significantly underestimates measured glomerular filtration rate in people with type 2 diabetes mellitus. Clin Biochem. 2018 Mar;53:43-48.
10. Oscanoa TJ, Amado JP, Romero-Ortuno R, Hidalgo JA. Estimation of the glomerular filtration rate in older individuals with serum creatinine-based equations: A systematic comparison between CKD-EPI and BIS1. Arch Gerontol Geriatr. 2018 Mar - Apr;75:139-145.