Technical brief on Cockroft-Gault Formula for estimating ... - LOINC

LOINC® <strong>Technical</strong> Brief
<strong>Technical</strong> <strong>brief</strong> on Cockcroft-Gault formula for estimating
creatinine clearance, Schwartz equation for Glomerular
Filtration Rate and MDRD formulae
Author: Gilbert Hill with edits by Clement J McDonald
1 Estimating creatinine clearance from serum creatinine
1.1 Cockcroft-Gault – not adjusted for body surface area (BSA)
The Cockcroft-Gault formula is used to estimate creatinine clearance from age, weight
and serum creatinine. The original paper from these two authors was Prediction of
Creatinine Clearance from Serum Creatinine, Nephron 1976;16:31- 41 hence the name.
Note that Creatinine clearance is a proxy for Glomerular Filtration Rate (GFR) and some
clinical settings describe this as an estimated GFR (see below).
The basic formula without normalization for BSA is represented in the LOINC data base
by the following term.
35591-7 Creatinine renal
clearance.predicted
And the formula is as follows
VRat Pt Ser/Plas Qn Cockcroft-Gault
formula
The equation as shown requires weight to be recorded in kg and creatinine in mg/dL, and
is valid for male patients. If the patient is female, the result should be multiplied by 0.85.
Web calculator for creatinine in mg/dL
If the patient’s weight is recorded in kg and the creatinine is reported in umol/L then
results from the above equation must be multiplied by 1.23 for men and 1.04 in women.
Web calculator for creatinine in umol/L
From http://www.sydpath.stvincents.com.au/other/CalcsCrClCGumol.htm
1.2 Cockcroft-Gault – adjusted for body surface area
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LOINC® <strong>Technical</strong> Brief
It is now common practice for the creatinine clearance calculated by the Cockcroft-Gault
formula to be normalized for a body surface area of 1.73 m 2 .
In particular, the Cockcroft-Gault BSA adjusted formula is used by many pharmacy
departments for medication dosage adjustments.
LOINC terms for BSA adjusted creatinine clearance
35592-5 Creatinine renal clearance/1.73
sq M.predicted
50380-5 Creatinine renal clearance/1.73
sq M.predicted.female
50381-3 Creatinine renal clearance/1.73
sq M.predicted.male
2 Direct prediction of GFR
2.1 Creatinine-based prediction of GFR
VRat Pt Ser/Plas Qn Cockcroft-Gault
formula, corrected
2
for BSA
VRat 24H Ser/Plas Qn Cockcroft-Gault
formula, corrected
for BSA
VRat 24H Ser/Plas Qn Cockcroft-Gault
formula, corrected
for BSA
2.1.1 Schwartz formula for Pediatrics
The Schwartz formula is used to predict GFR in pediatrics. The original paper by G F
Schwartz et al, is A Simple Estimate of GFR in Children Using Body Length and Plasma
Creatinine, Pediatrics 1976;58:259-263 has become more relevant in the last few years
because the MDRD formula (below) is specifically stated NOT to be applicable to
patients under 18 years of age. The Schwartz formula depends on age, gender, and body
height and serum creatinine. The equation can be stated as follows:
GFR Calculator for Children
Schwartz Formula
GFR (mL/min/1.73 m 2 ) = k (Height) / Serum Creatinine
k = Constant
o k = 0.33 in Preemie Infants
o k = 0.45 in Term infants to 1 year old
o k = 0.55 in Children to 13 years
o k = 0.65 in Adolescent males (Not females because of the presumed
increase in male muscle mass. The constant remains .55 for females.)
Height in cm
Serum Creatinine in mg/dl
Web calculator for Schwartz Formula

LOINC term for Schwartz formula
50384-7 Glomerular filtration rate/1.73 sq
M.predicted
LOINC® <strong>Technical</strong> Brief
VRat 24H Ser/Plas Qn Creatinine-based
formula (Schwartz)
2.1.2 MDRD 4 variables
The MDRD 4 variable equation is the principle equation recommended by professional
nephrology societies to estimate the GFR. It depends upon serum creatinine, age, gender
and race. It also includes a BSA adjustment term of 1.73 - the average body surface area
in an adult male. (Equations incorporating height and weight can be used to correct this
equation when patients are far from the mean in BSA- but are not routinely used.
The following is (taken from NKF MDR web site )
The National Kidney Disease Education Program (NKDEP) of the National
Institute of Diabetes and Diseases of the Kidney (NIDDK), National Kidney
Foundation (NKF) and American Society of Nephrology (ASN) recommend
estimating GFR from serum creatinine using the MDRD Study equation. This
equation depends upon the serum creatinine age, gender and race to estimate the
GFR and therefore improves upon several of the limitations with the use of serum
creatinine alone. The MDRD Study equation has been rigorously developed and
validated, and is more accurate than measured creatinine clearance from 24-hour
urine collections. The equation is:
GFR = 186 x (PCr) -1.154 x (age) -0.203 x (0.742 if female) x (1.210 if black)
GFR is expressed in ml/min/1.73 m 2. , In this equation Pcr serum creatinine must
be expressed in mg/dl, and age in years. (Of course other units can be used if the
right side of the above equation is multiplied by the appropriate constant). (all
taken from NKF web site - http://www.kidney.org/professionals/KLS/gfr.cfm#2
December 04 2006)
Web calculator for MDRD
The glomerular filtration rate predicted by the MDRD formula may be reported in at least
3 ways:
a) All four variables are known and used in the equation. The result would be race and
gender adjusted creatinine clearance.
b) Only two variables (serum creatinine and age) are used in the equation. In this
circumstance, the report may:
i) include a comment saying – “if patient is black multiple result by 1.21” and/or
“if patient is female multiply the result by .742”
or ii) may include two values: N1 if white and N2 if black, and a correction factor for
gender: if patient is female multiply the result by .742 .
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LOINC codes for MDRD formula
33914-3 Glomerular filtration rate/1.73 sq
M.predicted
48642-3 Glomerular filtration rate/1.73 sq
M.predicted.non black
48643-1 Glomerular filtration rate/1.73 sq
M.predicted.black
50044-7 Glomerular filtration rate/1.73.
sq M.predicted.female
LOINC® <strong>Technical</strong> Brief
VRat Pt Ser/Plas Qn Creatinine-based
formula (MDRD)
VRat Pt Ser/Plas Qn Creatinine-based
formula (MDRD)
VRat Pt Ser/Plas Qn Creatinine-based
formula (MDRD)
VRat Pt Ser/Plas Qn Creatinine-based
formula (MDRD)
2.1.3 MDRD 6 variables
A six variable version of the MDRD exists. This one depends on the patient’s serum
albumin and serum urea nitrogen values in addition to the MDRD-4 variables, but is not
the preferred equation for this estimate.
Where PCr=serum creatinine concentration (mg/dl) (alkaline picrate method);
SUN=serum urea nitrogen concentration (mg/dl) (urease method); Alb=serum albumin
concentration (g/dl) (bromocresol green method).
Taken from:
Stoves J,Lindley E,Barnfield M,Burniston T, Newstead C. MDRD equation estimates of
glomerular filtration rate in potential living kidney donors and renal transplant recipients
with impaired graft function.Nephrol Dial Transplant.2002,17: 2036-2037
2.2 Cystatin-based prediction of GFR
Although the MDRD equation, based on the measurement of serum creatinine, is the
most widely used method for estimating GFR, an alternative, based on the measurement
of serum cystatin is claimed to have certain advantages.
Estimating Glomerular Filtration Rate in Kidney Transplantation: A Comparison
between Serum Creatinine and Cystatin C-Based Methods, J Am Soc Nephrol 16: 3763–
3770, 2005
Web calculator for Cystatin-based GFR
LOINC code for GFR predicted by a cystatin-based formula
50210-4 Glomerular filtration rate/1.73 sq
M.predicted
VRat Pt Ser/Plas Qn Cystatin-based
formula
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