MDRD Calculator

MDRD method explained

The Modification of Diet in Renal Disease formula determines the estimated glomerular filtration rate which offers information about the overall function of the kidneys in adults.

The parameters required for calculation include:

■ Serum creatinine – measured in mg/dL;

■ Patient age – where the higher the age, the greater the risk of irregular kidney function;

■ Patient gender – the MDRD formula accounts for gender difference;

■ Patient race – African American people tend to have a greater GFR than Caucasian people at similar serum creatinine levels meaning adjustments are required.

In 1999, Levey et al. came with the Modification of Diet in Renal Disease formula:

eGFR = 175 x (Serum Creatinine)^-1.154 x (Age)^-0.203 x (0.742 only if female) x (1.212 only if black)

The above formula can only be used in estimating GFR in stable chronic kidney disease and is not addressed to patients with acute renal failure. The method has been validated and has shown better correlation than other GFR estimation calculations, such as the Cockcroft-Gault formula.

The Working Group set the upper reporting limit at 90 mL/min/1.73 m², meaning that all values above this threshold should be referred to as "> 90 mL/min/1.73 m2" rather than directly specified.

In terms of age related normal values, for patients aged 70 and above, eGFR values of 45 to 59 mL/min/1.73 m² are considered typical when in the absence of kidney damage signs and when unrelated to chronic kidney disease-related complications.

The second tab of the calculator offers an estimation of GFR that can be used for pediatric patients, based on serum creatinine and height, the former helping to determine the body surface area.

GFR guidelines

GFR estimation provides insight into the basic renal function without the need of invasive investigations. The results obtained are adapted for a standard body surface area of 1.73 m².

Glomerular filtration rate represents the amount of blood filtered by the capillaries of the kidney into the Bowman capsules (filtration and elimination of toxins in urine) in a certain amount on time.

GFR values above 90 mL/min/1.73 m² are considered normal in the absence of any kidney disease evidence.

Regardless of GFR value, if proteinuria, haematuria, polycystic kidney or any other abnormalities are present, the result is likely to be consistent with chronic kidney disease (CKD) stage 1.

GFR values between 60 and 89 mL/min/1.73 m² indicate reduced kidney filtration function and if associated with any of the above conditions, are suggestive of CKD stage 2.

The following table summarizes the National Kidney Foundation Kidney Disease Outcome Quality Initiative (K/DOQI) classification:

There is criticism of the estimation methods through serum creatinine because they are based on a 24h prediction of excretion rate which is highly dependent on muscle mass because creatinine is break down product of the muscular creatinine phosphate.

This means that values for two people with different muscle mass but similar serum creatinine will be different in terms of kidney filtration.

Other sources state that creatinine clearance overestimates the rate of glomerular filtration by 10 up to 20%.

Original source

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; 130(6):461-70.

Other references

1. Levey AS, Coresh J, Greene T, Marsh J, Stevens LA, Kusek JW, Van Lente F; Chronic Kidney Disease Epidemiology Collaboration. Expressing the Modification of Diet in Renal Disease Study equation for estimating glomerular filtration rate with standardized serum creatinine values. Clin Chem. 2007; 53(4):766-72.

2. National Kidney Foundation. K/DOQI clinical practice guidelines for chronic kidney disease: evaluation, classification, and stratification. Am J Kidney Dis. 2002; 39(2 Suppl 1): S1-266.