Summary

Usage

CKD-EPI Equations are the standard used to measure kidney function in patients with stable, chronic kidney disease (not acute). These equations use creatinine or a combination of creatinine and cystatin C to measure creatinine clearance as a proxy to estimate glomerular filtration rate(rate).

The 2021 CKD-EPI creatinine-cystatin C version is the recommended standard and the 2021 CKD-EPI creatinine version is currently recommended by the ASN and NKF for GFR reporting in the United States. However, cystatin C is not available in all laboratories. Yet, the creatinine-based version is adequate for many clinical applications even though the combined creatinine and cystatin C can add accuracy. However, specific populations, such as diabetics, pregnant women, and individuals with unusual body mass (obese, amputees, and severe malnutrition), are at risk for less accurate creatinine-based estimates of kidney function. The 2021 CKD-EPI creatinine-cystatin may offer improved accuracy in these special populations with the addition of cystain C, and is recommended as a confirmatory test in patients with extremes of body composition, to include body fat or muscle mass. CKD-EPI is not indicated for patients on dialysis.

Some of the CKD-EPI equations include adjustments based on race. However, adjustments base on race appear to be controversial and the pros/cons of adjustments ought to be part of a shared decision-making approach between the clinician and the patient. For more information on the topic of eGFR equations and race, NephJC (FitzGerald, 2019) provides an excellent primer on the subject.

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Summary

The CKD-EPI (creatinine) was developed by Levey et al (2009).

Uses the new gold standard: Clearance of iothalamate
Uses linear regression to estimate the logarithm of measured GFR from standardized creatinine levels, sex, race, and age.

2021 CKD-EPI Creatinine

= 142 x (Scr/A)^B x 0.9938^age x (1.012 if female)
A & B as follows:

Female:		Male:
Scr ≤ 0.7	A= 0.7	Scr ≤ 0.9	A= 0.9
	B= -0.241		B= -0.302

Scr > 0.7	A= 0.7	Scr > 0.9	A= 0.9
	B= -1.2		B= -1.2

2021 CKD-EPI Creatinine-Cystatin C

= 135 x (Scr/A)^B x (Scys/C)^D x 0.9961^age x (0.963 if female)
A, B, C & D as follows:

Female:			Male:
	Scr ≤ 0.7	Scr > 0.7		Scr ≤ 0.9	Scr > 0.9
Scys ≤ 0.8	A= 0.7	A= 0.7	Scys ≤ 0.8	A= 0.9	A= 0.9
	B= -0.219	B= -0.544		B= -0.144	B= -0.544
	C= 0.8	C= 0.8		C= 0.8	C= 0.8
	D= -0.323	D= -0.323		D= -0.323	D= -0.323

Scys > 0.8	A= 0.7	A= 0.7	Scys > 0.8	A= 0.9	A= 0.9
	B= -0.219	B= -0.544		B= -0.144	B= -0.544
	C= 0.8	C= 0.8		C= 0.8	C= 0.8
	D= -0.778	D= -0.778		D= -0.778	D= -0.778

2009 CKD-EPI Creatinine*

= A x (Scr/B)^C x 0.993^Age x (1.159 if black)
A, B & C as follows:

Female:		Male:
Scr ≤ 0.7	A= 144	Scr ≤ 0.9	A= 141
	B= 0.7		B= 0.9
	C= -0.329		C= -0.411

Scr > 0.7	A= 144	Scr > 0.9	A= 141
	B= 0.7		B= 0.9
	C= -1.209		C= -1.209

2012 CKD-EPI Cystatin C

= 133 x (scys/0.8)^A x 0.996^age x B
A& B as follows:

Female:		Male:
Scys ≤ 0.8	A= -0.499	A= -0.499
	B= 0.932	B= 1

Scys > 0.8	A= -1.328	A= -1.328
	B= 0.932	B= 1

2012 CKD-EPI Creatinine-Cystatin C*

= A x (Scr/B)^C x (Scys/0.8)^D x 0.995^age x (1.08 if Black)
A, B, C, & D as follows:

Female:			Male:
	Scr ≤ 0.7	Scr > 0.7		Scr ≤ 0.9	Scr > 0.9
Scys ≤ 0.8	A= 130	A=130	Scys ≤ 0.8	A= 135	A= 135
	B= 0.7	B= 0.7		B= 0.9	B= 0.9
	C= -0.248	C= -0.601		C= -0.207	C= -0.601
	D= -0.375	D= -0.375		D= -0.375	D= -0.375

Scys > 0.8	A= 130	A= 130	Scys > 0.8	A= 135	A= 135
	B= 0.7	B= 0.7		B= 0.9	B= 0.9
	C= -0.248	C= -0.601		C= -0.207	C= -0.601
	D= -0.711	D= -0.711		D= -0.711	D= -0.711

*Race may or may not provide better estimates of GFR. Using the adjustment coefficient for black patients is controversial (Inker et al, 2021) and is an optional component.

Abbreviations

Scr = serum creatinine (mg/dL)
Scys = serum cystatin C (mg/L)
GFR = glomerular filtration rate (ml/min/1.73 m²)

Chronic Kidney Disease (CKD) Staging

GFR Stage	GFR Description	GFR Range
I	Normal or High	≥90
II	Mildly decreased	60-89
IIIa	Mildly to moderately decreased	45-59
IIIb	Moderately to severely decreased	30-44
IV	Severely decreased	15-29
V	Kidney failure	<15

Source: KIDGO 2012 Clinical Practice Guidelines

Instructions

For use in patients with stable, chronic kidney disease to measure kidney function.

The 2021 CKD-EPI equation is now the recommended standard.

To improve accuracy the combined creatinine and cystatin C equation is preferred. It is also recommended as a confirmatory test in patients with extreme body composition (e.g. malnourished, amputees, obese patients, high or low muscle mass) and special populations, including pregnancy and diabetes, as creatinine-based estimates are less accurate in these contexts.
However, serum cystatin C is not as widely available. The creatinine-based equation is still adequate for many clinical contexts, and is currently recommended for GFR reporting in the United State.
Not for use in patients on dialysis.

Adjustments based on race

The 2021 versions presented here do not include race but the 2009 and the 2012 CKD-EPI creatinine and creatinine-cystatin C versions do include race. However, adjustments base on race appear to be controversial, and the pros/cons of adjustments ought to be part of a shared decision-making approach between the clinician and the patient. For more information on the topic of eGFR equations and race, NephJC (FitzGerald, 2019) provides an excellent primer on the subject.

Literature

A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009 May 5;150(9):604-12. — Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF 3rd, Feldman HI, Kusek JW, Eggers P, Van Lente F, Greene T, Coresh J; CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration).
Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012 Jul 5;367(1):20-9. — Inker LA, Schmid CH, Tighiouart H, Eckfeldt JH, Feldman HI, Greene T, Kusek JW, Manzi J, Van Lente F, Zhang YL, Coresh J, Levey AS; CKD-EPI Investigators.
New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med. 2021 Nov 4;385(19):1737-1749. — Inker LA, Eneanya ND, Coresh J, Tighiouart H, Wang D, Sang Y, Crews DC, Doria A, Estrella MM, Froissart M, Grams ME, Greene T, Grubb A, Gudnason V, Gutiérrez OM, Kalil R, Karger AB, Mauer M, Navis G, Nelson RG, Poggio ED, Rodby R, Rossing P, Rule AD, Selvin E, Seegmiller JC, Shlipak MG, Torres VE, Yang W, Ballew SH, Couture SJ, Powe NR, Levey AS; Chronic Kidney Disease Epidemiology Collaboration.
KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease — Kidney Disease Improving Global Outcomes (KDIGO)
KDIGO 2022 Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease — Kidney Disease Improving Global Outcomes (KDIGO)
Reconsidering the consequences of using race to estimate kidney function. JAMA. 2019; 322(2):113-114. — Eneanya ND, Yang W, Reese PP

CKD-EPI Equations for Glomerular Filtration Rate (GFR)

Summary

Instructions

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