Implications of the CKD-EPI GFR Estimation Equation in Clinical Practice

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Figure 1.
Age distribution of stage 3 to 5 CKD population on the basis of estimating equations. (A) Population classified with CKD by both CKD-EPI and MDRD (n = 46,985). (B) Population classified with CKD only by MDRD (n = 5951). (C) Population classified with CKD only by CKD-EPI (n = 823).
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Figure 2.
(A) Time to classification of CKD by age on the basis of the MDRD equation. (B) Time to classification of CKD by age on the basis of the CKD-EPI equation. *Extrapolated time assuming a Weibull survival distribution.

Table 1.

Demographic characteristics of patients classified with CKD on the basis of the MDRD and the CKD-EPI equation

Patient Characteristics	Method of CKD Classification			Percentage of Change in CKD Patients on the Basis of the CKD-EPI Equation
Patient Characteristics	Both MDRD and CKD-EPI Equations	MDRD Equation Only	CKD-EPI Equation Only
Age 18 to 59 (n = 11,413)	65%	35%	0%	−35%
Age 60 to 69 (n = 12,301)	89%	11%	0%^{^b}	−11%
Age 70 to 79 (n = 16,286)	96%	4%	1%	−3%
Age 80 to 89 (n = 12,033)	96%	0%	4%	4%
Age 90+ (n = 1726)	91%	0%	9%	10%
African American (n = 6251)	93%	3%	4%	2%
Non-African American (n = 47,508)	87%	12%	1%	−11%
Diabetes present (n = 11,004)	91%	7%	1%	−6%
Diabetes absent (n = 42,755)	86%	12%	2%	−11%
Male gender (n = 23,779)	89%	9%	2%	−7%
Female gender (n = 29,980)	86%	13%	1%	−12%
BMI <20 kg/m² (n = 1813)	88%	9%	3%	−6%
BMI 20 to 24 kg/m² (n = 11,052)	87%	10%	2%	−8%
BMI 25 to 29 kg/m² (n = 17,719)	88%	10%	2%	−9%
BMI 30 to 34 kg/m² (n = 10,858)	87%	12%	1%	−11%
BMI 35+ kg/m² (n = 8113)	85%	15%	0%^{^b}	−14%
BMI missing (n = 4204)	90%	8%	2%	−7%
Primary insurance: Medicare (n = 29,223)	94%	4%	2%	−2%
Primary insurance: Medicaid (n = 1012)	82%	18%	0%^{^b}	−18%
Primary insurance: other (n = 22,283)	79%	20%	1%	−19%
Primary insurance: unknown (n = 1241)	79%	20%	1%	−20%
Year of initial GFR: 2005 (n = 28,275)^{^a}	92%	7%	1%	−6%
Year of initial GFR: 2006 (n = 10,586)^{^a}	85%	13%	2%	−11%
Year of initial GFR: 2007 (n = 7393)^{^a}	81%	17%	2%	−15%
Year of initial GFR: 2008 (n = 5166)^{^a}	79%	18%	3%	−16%
Year of initial GFR: 2009 (n = 2339)^{^a}	78%	19%	3%	−16%
Overall n (%)	46,985 (87%)	5951 (11%)	823 (2%)	−10%

The study excluded 3,877 patients identified with CKD on the basis of diagnosis codes alone. The row percentages may not sum to 100 because of rounding.
↵a Minimum date of eGFR <60 ml/min per 1.73 m² on the basis of either the MDRD or CKD-EPI equation.
↵b The values are <0.5%.

Table 2.

Proportion of study population with ICD-9 diagnostic codes indicative of kidney disease

Patient Group	ICD-9 Diagnosis Conditions					Any Listed Condition (%)
Patient Group	CKD (%)	Hypertensive Nephrosclerosis (%)	Diabetic Nephropathy (%)	GN (%)	PKD (%)	Any Listed Condition (%)
Age 18 to 59	15.9	4.4	4.3	1.7	1.2	18.8
Age 60 to 69	12.6	2.5	3.3	0.5	0.3	14.6
Age 70 to 79	11.4	2.4	2.5	0.3	0.1	13.1
Age 80 to 89	8.7	1.9	1.1	0.1	0.0	10.0
Age 90+	6.5	1.0	0.5	0.0	0.0	7.2
All patients	11.7 (n = 6266)	2.6 (n = 1406)	2.6 (n = 1400)	0.6 (n = 297)	0.3 (n = 185)	13.8 (n = 7266)

The study population consisted of patients with CKD as determined by either the CKD-EPI or MDRD GFR estimating equations. The ICD-9 diagnostic codes used were: CKD = 585, 585.1, 585.2, 585.3, 585.4, 585.5, 585.6, 585.9; Diabetic nephropathy = 250.4, 250.40, 250.41, 250.42, 250.43; glomerulonephritis = 580, 580.0, 580.4, 580.8, 580.81, 580.89, 580.9, 582, 582.1, 582.2, 582.4, 582.8, 582.81, 582.89, 582.9; Polycystic kidney disease = 753.12, 753.13, 753.14; Hypertensive nephrosclerosis = 403, 403.0, 403.00, 403.01, 403.1, 403.10, 403.9, 403.90, 403.91. GN, glomerulonephritis; PKD, polycystic kidney disease.

Table 3.

Difference in estimated GFR by the MDRD and CKD-EPI at the time of CKD

Patient Characteristics	Average Difference (± SD) in eGFR in ml/min per 1.73 m² (CKD-EPI − MDRD)^{^a}	Percentage of Patients with eGFR on the Basis of CKD-EPI ± 5 ml/min per 1.73 m² Different from eGFR on the Basis of MDRD	Percent of Patients with eGFR on the Basis of CKD-EPI ≥10% Different from eGFR on the Basis of MDRD
Age 18 to 59 (n = 7379)	2.84 ± 1.84	8.8	5.8
Age 60 to 69 (n = 10,982)	1.43 ± 1.34	0	0.6
Age 70 to 79 (n = 15,688)	−0.33 ± 1.14	0	1.1
Age 80 to 89 (n = 12,033)	−1.89 ± 1.07	1.3	4.4
Age 90+ (n = 1726)	−3.60 ± 1.17	9.4	26.7
African American (n = 6095)	−1.51 ± 2.10	5.3	14.3
Non-African American (n = 41,713)	0.28 ± 2.11	2.0	2.4
Diabetes present (n = 10,213)	0.09 ± 2.07	1.8	3.2
Diabetes absent (n = 37,595)	0.04 ± 2.23	2.6	4.0
Male gender (n = 21,745)	−0.42 ± 2.07	1.6	4.0
Female gender (n = 26,063)	0.45 ± 2.22	3.1	3.7
BMI <20 kg/m² (n = 1656)	−0.33 ± 2.46	4.7	8.5
BMI 20 to 24 kg/m² (n = 9935)	−0.36 ± 2.27	3.0	5.3
BMI 25 to 29 kg/m² (n = 15,905)	−0.12 ± 2.10	2.0	3.1
BMI 30 to 34 kg/m² (n = 9528)	0.37 ± 2.07	2.1	2.6
BMI 35 + kg/m² (n = 6930)	1.08 ± 2.02	2.5	2.3
BMI missing (n = 3854)	−0.60 ± 2.15	2.5	6.5
Primary insurance: Medicare (n = 28,165)	−0.50 ± 1.90	1.3	4.0
Primary insurance: Medicaid (n = 832)	1.59 ± 2.31	7.1	7.6
Primary insurance: other/unknown (18,811)	0.81 ± 2.34	3.6	3.4
Overall (n = 47,808)	0.05 ± 2.20	2.4	3.8