*! version 2.02 03aug2021

help for egfrVersion 2.02, 3 August 2021

Title

egfr -- Calculate estimated glomerular filtration rate (eGFR) from creatinine
and/or cystatin C and other variables

Syntax

egfr [if] [in], options

formula(formula_name) formula to use. Supported formulae are mdrd4 (the
default), mdrd6, ckdepi, ckdepi_cyc, ckdepi_cr_cyc, mayo, cg,
nankivell and schwartz

creatinine(varname) serum creatinine

cystatinc(varname) serum cystatin C in mg/L

female(expr) expression indicating subject is female

age(varname) age in years

prem(expr) expression indicating child was born prematurely

height(varname) height in cm

weight(varname) weight in kg

urea(varname) urea; assumed to be recorded in mmol/L unless option
us specified

albumin(varname) albumin; assumed to be recorded in g/L unless option
us specified

black(expr) expression indicating subject is black

us use US units for creatinine, urea and albumin

standard creatinine is standardised or traceable to IMDS

generate(varname) name of eGFR variable (default is egfr_formula_name)

replace replace existing variable

Description

egfr calculates estimated glomerular filtration rate (eGFR) in mL/min based on the serum
creatinine and/or cystatin C along with various other variables. The exact variables required depend
on the eGFR formula used and the options that the user specifies.

Options for egfr

formula(formula_name) specifies the formula to use in calcuating the eGFR. The formulae
supported are:

mdrd4 4-variable MDRD equation. This is the default when the formula option is not
specified. This formula requires the age and female options to be specified. Subjects are
assumed to be non-black unless the black option is also specified. Non-standardised serum
creatinine values are assumed unless the standard option is used.

mdrd6 6-variable MDRD equation. This formula requires the age, female, urea and
albumin options to be specified. Subjects are assumed to be non-black unless the black
option is also specified. Non-standardised serum creatinines are assumed unless the standard
option is used.

ckdepi Original creatinine-only CKD-EPI formula. This formula requires the creatinine,
age and female options to be specified. Subjects are assumed to be non-black unless the
black option is also specified. Standardised serum creatinines are assumed.

ckdepi_cyc CKD-EPI cystatin C formula. This formula requires the cystatinc, age and
female options to be specified.

ckdepi_cr_cyc CKD-EPI creatinine-cystatin C formula. This formula requires the creatinine,
cystatinc, age and female options to be specified. Subjects are assumed to be
non-black unless the black option is also specified. Standardised serum creatinines are assumed.

mayo Mayo quadratic formula. This formula requires the age and female options to be
specified.

cg Cockroft-Gault formula. This formula requires the age, female and weight
options to be specified.

nankivell Nankivell formula for kidney transplant patients. This formula requires the
female, urea, height and weight options to be specified.

schwartz Schwartz formulae for children. If the standard option is not specified then the
k constants for non-standardised creatinines are used; determining these requires the age,
female, height and prem options to be specified and the eGFR is only calculated for
subjects aged 21 or younger. If the standard option is specified then a k constant of
0.413 is used; in this case only the height option needs to be specified.

creatinine(varname) specifies the variable containing the serum creatinine. This option is
required for every eGFR formula apart from the CKD-EPI cystatin C formula. It is assumed to be
recorded in SI units (micromol/L). If the us option is specified the units are assumed to be
mg/dL.

cystatinc(varname) specifies the variable containing the serum cystatin C in mg/L.

female(expr) specifies an expression which evaluates as true when the subject is female. For
example, female(sex=="F")

age(varname) specifies a variable containing the subject's age in years.

prem(expr) specifies an expression which evaluates as true when the subject was born
prematurely. For example, prem(premature=="Y")

height(varname) specifies a variable containing the subject's height in cm.

weight(varname) specifies a variable containing the subject's weight in kg.

urea(varname) specifies a variable containing the urea. By default this is interpreted as the
serum urea concentration in SI units (mmol/L). However, if the us option is specified, it is
interpreted as the blood urea nitrogen (BUN) in mg/dL.

albumin(varname) specifies a variable containing the albumin. By default this is assumed to be
recorded in SI units of g/L. If the us option is specified the units are assumed to be g/dL.

black(expr) specifies an expression which evaluates as true when the subject is black. For
example, black(race=="AA")

us interpret creatinine, urea and albumin as being recorded in US units rather than SI units.
See the creatinine, urea and albumin options for more details.

standard specifies that the creatinine values are standardised or traceable to isotope
dilution mass spectrometry (IDMS) (see Myers et al 2006). Without this option the creatinine values
are assumed to be non-standardised.

generate(varname) allows you to specify the name of the new variable containing the eGFR.
Without this option the new variable is named egfr_formulaname eg egfr_mdrd4

replace replace existing eGFR variable if it exists. If you use if or in, the
eGFR will only be overwritten in those observations meeting the if and in criteria.

Examples

. egfr, cr(creat) age(age) female(sex=="F")

. egfr, cr(creat) age(age) female(sex=="F" if !missing(sex))

. egfr, cr(creat) age(age) female(sex=="F") black(black==1) gen(eGFR) replace

. egfr, f(mdrd6) cr(creat) standard age(age) fem(sex=="F") urea(urea) alb(albumin) us

. egfr if age<=21, f(schwartz) cr(creat) s height(height)

Saved results

egfr saves the summary statistics of the newly created eGFR values in r()

Formuale

4-variable MDRD equation:

Without standardised creatinine (Levey et al 2000):

eGFR = 186 x Cr^-1.154 x age^-0.203 x 1.212 if black x 0.742 if female

With standardised creatinine (Levey et al 2006):

eGFR = 175 x Cr^-1.154 x age^-0.203 x 1.212 if black x 0.742 if female

where Cr is creatinine in mg/dL and age is age in years

6-variable MDRD equation:

Without standardised creatinine (Levey et al 1999):

eGFR = 170 x Cr^-0.999 x age^-0.176 x BUN^-.170 x alb^0.318
x 1.18 if black x 0.762 if female

With standardised creatinine (Levey et al 2006):

eGFR = 161.5 x Cr^-0.999 x age^-0.176 x BUN^-.170 x alb^0.318
x 1.18 if black x 0.762 if female

where Cr is creatinine in mg/dL, age is age in years, BUN is blood urea
nitrogen (mg/dL) and alb is albumin (g/dL)

CKD-EPI creatinine equation (Levey et al 2009):

Females with Cr<=62 micromol/L:

eGFR = (144 + 22 if black) x (Cr/0.7)^-0.329 x 0.993^age

Females with Cr>62 micromol/L:

eGFR = (144 + 22 if black) x (Cr/0.7)^-1.209 x 0.993^age

Males with Cr<=80 micromol/L:

eGFR = (141 + 22 if black) x (Cr/0.9)^-0.411 x 0.993^age

Males with Cr<=80 micromol/L:

eGFR = (141 + 22 if black) x (Cr/0.9)^-1.209 x 0.993^age

where Cr is creatinine in mg/dL and age is age in years

CKD-EPI cystatin C equation (Inker et al 2012):

eGFR = 133 x min(CyC/0.8, 1)^-0.499 x max(CyC/0.8, 1)^-1.328 x 0.996^age
x 0.932 if female

where CyC is cystatin C in mg/L and age is age in years

CKD-EPI creatinine-cystatin C equation (Inker et al 2012):

eGFR = 135
x min(Cr/K, 1)^a x max(Cr/K, 1)^-0.601
x min(CyC/0.8, 1)^-0.375 x max(CyC/0.8, 1)^-0.711
x 0.995^age x 0.969 if female x 1.08 if black

where Cr is creatinine in mg/dL, CyC is cystatin C in mg/L, K is 0.7 for
females and 0.9 for males, a is -0.248 for females and -0.207 for males, and age is age in
years

Mayo quadratic formula (Rule et al 2004):

If Cr>=0.8 mg/dL:

eGFR = exp(1.911 + 5.249/Cr - 2.114/Cr^2 - 0.00686xage - 0.205 if female)

If Cr<0.8 mg/dL:

eGFR = exp(1.911 + 5.249/0.8 - 2.114/0.8^2 - 0.00686xage - 0.205 if female)

where Cr is creatinine in mg/dL and age is age in years

Cockgroft-Gault formula (Cockroft and Gault 1976):

eGFR = (140 - age) x weight x (1.04 if female, 1.23 if male) / Cr

where Cr is creatinine in micromol/L, age is age in years and weight is weight
in kg

Nankivell formula (Nankivell et al 1995):

eGFR = 6.7/(Cr/1000) + 0.25xweight - 0.5xurea - 100/(height/100)^2 +
(25 if female, 35 if male)

where Cr is creatinine in micromol/L, weight is weight in kg, urea is serum
urea in mmol/L and height is height in cm

Schwartz formulae for children:

eGFR = k x height/Cr

where Cr is creatinine in mg/dL, height is height in cm and

k=0.413 if standardised creatinine used (Schwartz et al 2009), otherwise:

k=0.33 if age<1 year and subject was premature (Brion et al 1986)

k=0.45 if age<1 year and subject was not premature (Schwartz et al 1984)

k=0.55 if age>=1 and <13 years (Schwartz et al 1976)

k=0.55 if age>=13 and <=21 years and female (Schwartz et al 1976)

k=0.70 if age>=13 and <=21 years and male (Schwartz et al 1985)

References

Brion LP, Fleischman AR, McCarton C, Schwartz GJ. A simple estimate of glomerular filtration
rate in low birth weight infants during the first year of life: noninvasive assessment of body
composition and growth. J Pediatr. 1986 Oct.;109(4):698Ð707.

Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine.
Nephron. 1976;16(1):31-41.

Inker LA, Schmid CH, Tighiouart H, Eckfeldt JH, Feldman HI, Greene T, et al. Estimating
glomerular filtration rate from serum creatinine and cystatin C.
N Engl J Med. 2012 Jul 5;367(1):20Ð9.

Levey AS, Bosch JP, Lewis JB, Greene T, Rogers N, Roth D. A more accurate method to estimate
glomerular filtration rate from serum creatinine: a new prediction equation.
Modification of Diet in Renal Disease Study Group.
Ann Intern Med. 1999 Mar. 16;130(6):461-470.

Levey AS, Stevens LA, Schmid CH, Zhang YL, Castro AF, Feldman HI, et al.
A new equation to estimate glomerular filtration rate.
Ann Intern Med. 2009 May 5;150(9):604-612.

Levey AS, Coresh J, Greene T, Stevens LA, Zhang YL, Hendriksen S, et al.
Using standardized serum creatinine values in the modification of diet in renal disease
study equation for estimating glomerular filtration rate.
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Levey A, Greene T, Kusek J, Beck G. A simplified equation to predict glomerular filtration
rate from serum creatinine (abstract). J Am Soc Nephrol. 2000 May 20;11(11):155A.
Available from: http://nephron.org/nephsites/nic/mdrdgfr

Myers GL, Miller WG, Coresh J, Fleming J, Greenberg N, Greene T, et al. Recommendations for
improving serum creatinine measurement: a report from the Laboratory Working Group of the National
Kidney Disease Education Program. Clin Chem. 2006 Jan.;52(1):5-18.

Nankivell BJ, Gruenewald SM, Allen RD, Chapman JR. Predicting glomerular filtration rate
after kidney transplantation. Transplantation. 1995 Jun. 27;59(12):1683-1689.

Rule AD, Larson TS, Bergstralh EJ, Slezak JM, Jacobsen SJ, Cosio FG. Using serum creatinine
to estimate glomerular filtration rate: accuracy in good health and in chronic kidney disease.
Ann Intern Med. 2004 Dec. 21;141(12):929-937.

Schwartz GJ, Haycock GB, Edelmann CM, Spitzer A. A simple estimate of glomerular filtration
rate in children derived from body length and plasma creatinine.
Pediatrics. 1976 Aug.;58(2):259-263.

Schwartz GJ, Feld LG, Langford DJ. A simple estimate of glomerular filtration rate in
full-term infants during the first year of life. J Pediatr. 1984 Jun.;104(6):849-854.

Schwartz GJ, Gauthier B. A simple estimate of glomerular filtration rate in adolescent boys.
J Pediatr. 1985 Mar.;106(3):522-526.

Schwartz GJ, Mu–oz A, Schneider MF, Mak RH, Kaskel F, Warady BA, et al. New equations to
estimate GFR in children with CKD. J Am Soc Nephrol. 2009 Mar. 1;20(3):629-637.

Author

Phil Clayton, ANZDATA Registry, Australia, phil@anzdata.org.au