# Cockcroft-Gault formula, Schwartz equation

Last Updated: 2020-06-09 (10 months ago)

Authors: Gilbert Hill, MD, PhD with edits by Clement J McDonald, MD

Date Written: 2007-11-20

**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 | VRat | Pt | Ser/Plas | Qn | Cockcroft-Gault formula |

And the formula is as follows:

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**

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 m2.

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 | VRat | Pt | Ser/Plas | Qn | Cockcroft-Gault formula, corrected for BSA |

50380-5 | Creatinine renal clearance/1.73 sq M.predicted.female | VRat | 24H | Ser/Plas | Qn | Cockcroft-Gault formula, corrected for BSA |

50381-3 | Creatinine renal clearance/1.73 sq M.predicted.male | VRat | 24H | Ser/Plas | Qn | Cockcroft-Gault formula, corrected for BSA |

**2 Direct prediction of GFR**

**2.1 Creatinine-based prediction of GFR**

#### 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, sex, and body height and serum creatinine. The equation can be stated as follows:

**GFR Calculator for Children**

**Schwartz Formula**

GFR (mL/min/1.73 m2) = k (Height) / Serum Creatinine

- k = Constant
- k = 0.33 in Preemie Infants
- k = 0.45 in Term infants to 1 year old
- k = 0.55 in Children to 13 years
- 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 | 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, sex 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 they are not routinely used.)

The following was taken from NKF MDR web site on December 4, 2006 (http://www.kidney.org/professionals/KLS/gfr.cfm#2):

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, sex 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 m2. 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 -

The glomerular filtration rate predicted by the MDRD formula may be reported in at least three ways:

- All four variables are known and used in the equation. The result would be race and sex adjusted creatinine clearance.
- Only two variables (serum creatinine and age) are used in the equation. In this circumstance, the report may:
- include a comment saying – “if patient is black, multiply result by 1.21” and/or “if patient is female, multiply the result by .742”, or
- may include two values: N1 if white and N2 if black, and a correction factor for sex: if patient is female, multiply the result by .742.

**LOINC codes for MDRD formula**

33914-3 | Glomerular filtration rate/1.73 sq M.predicted | VRat | Pt | Ser/Plas | Qn | Creatinine-based formula (MDRD) |

48642-3 | Glomerular filtration rate/1.73 sq M.predicted.non black | VRat | Pt | Ser/Plas | Qn | Creatinine-based formula (MDRD) |

48643-1 | Glomerular filtration rate/1.73 sq M.predicted.black | VRat | Pt | Ser/Plas | Qn | Creatinine-based formula (MDRD) |

50044-7 | Glomerular filtration rate/1.73 sq M.predicted.female | 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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