eGFR Calculator By CKD-EPI

The CKD-EPI equation

This is the recommended method for laboratory estimation of GFR based on serum creatinine, patient age, gender and race. CKD-EPI comes from Chronic kidney disease epidemiology collaboration.

By providing eGFR, the method helps assess renal function and can be used for patients over 18.

eGFR = 141 X min(Cr/κ,1)α X (max(Cr/κ,1)^-1.209) X (0.993^Age) X 1.018 [if female] X 1.159 [if black]

Where:

■ Cr- is serum creatinine in mg/dL;

■ k is 0.7 for women, 0.9 for men;

■ α is –329 for women and –0.411 for men.

The CKD-EPI was found to be more accurate than the MDRD formula (Modification of Diet in Renal Disease) and improves estimation especially in the interval where GFR values were often underestimated (60- 120 mL/min).

In comparison, the equation in question uses the same four variables as the MDRD but a different relationship for age, gender and race and a 2-slope “spline” to model relationship between serum creatinine and eGFR.

About the study

A study conducted by Levey et al. in 2009 led to the creation of a new equation for estimating GFR, aimed at improving laboratory testing and at addressing issues of the older equations, such as the MDRD.

A sample of 8254 participants in 10 studies was used for the equation development and a sample of 3896 participants in 16 studies for the validation set.

One of the pitfalls of the study comes from the samples used which only contained a limited number of elderly people and racial and ethnic minorities, although the equation provides for such groups.

In the study, GFR was measured as the clearance of exogenous filtration markers. Linear regression was used to estimate the logarithm of measured GFR from standardized creatinine levels, gender, race, and age.

The CKD-EPI was found to perform better than the MDRD in the validation set, especially at high GFRs.

eGFR levels and CKD stages

Chronic kidney disease is the name given to a series of conditions in which the kidneys gradually lose their function. According to the National Kidney Foundation, the two main causes of CKD are diabetes and high blood pressure.

Normal glomerular filtration rate should be 100 mL/min/1.73m², but any value above 90 is considered to be normal function.

However, in case there are other signs of chronic disease, despite a theoretically healthy eGFR, the patient is likely to be in stage 1.

You can find the five stages of chronic kidney disease explained in the table below:

Patients suffering from chronic kidney disease (any stage) are considered at risk of heart, blood vessel disease or stroke. The estimation of GFR is an essential part of diagnosis and is required at least 2 times, 90 days apart.

Original source

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). A new equation to estimate glomerular filtration rate. Ann Intern Med. 2009; 150(9):604-12.

Other references

1. Matsushita K, Selvin E, Bash LD, Astor BC, Coresh J. Risk implications of the new CKD Epidemiology Collaboration (CKD-EPI) equation compared with the MDRD Study equation for estimated GFR: the Atherosclerosis Risk in Communities (ARIC) Study. Am J Kidney Dis. 2010; 55(4):648-59.

2. Mathew TH, Johnson DW, Jones GR. Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: revised recommendations. The Medical Journal of Australia. 2007; 187 (8): 459–63.

3. Johnson DW, Jones GR, Mathew TH, Ludlow MJ, Doogue MP, Jose MD, Langham RG, Lawton PD, McTaggart SJ, Peake MJ, Polkinghorne K, Usherwood T; Australasian Creatinine Consensus Working Group. Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: new developments and revised recommendations. Med J Aust. 2012; 197(4):224-5.