A measured GFR is considered the most accurate way to detect changes in kidney status. If kidney damage is detected early, it may be possible to prevent worsening damage if this is due to high blood pressure, diabetes or to other treatable diseases. However, measuring GFR is complicated and requires experienced personnel. Because eGFR can be calculated based on serum creatinine, an easily performed and commonly used laboratory test, it is possible to get a reasonable estimate of the actual GFR.

The creatinine clearance test also provides an estimate of renal function and of the actual GFR. However, in addition to the serum creatinine, this test requires a timed urine collection (24 hours) for creatinine measurement in order to calculate the clearance.

Another method of evaluating renal function involves the measurement of the serum level of a molecule called cystatin C. There is increasing interest in the use of this test for this purpose.

The eGFR can be determined, with no extra testing, at the same time that a sample is sent for creatinine measurement. The National Kidney Foundation (NKF) has recommended that it be calculated automatically every time a creatinine test is done. If you have had a creatinine measurement, you can calculate the eGFR yourself by using the calculator on the National Kidney Foundation website.

Compared to serum creatinine, the eGFR more reliably detects kidney disease in its early stages. Because the calculation works best for estimating reduced renal function, the NKF suggests only reporting actual results once values are < 60 ml/min (normal values are 90-120 ml/min, according to the NKF). An eGFR below 60 ml/min suggests that some kidney damage has occurred. The NKF recommends that your eGFR result be interpreted in relation to your clinical history and presenting conditions.

The NKF has suggested that all persons “know their GFR number.” They recommend interpreting GFR (usually by eGFR) based on the following table:

  

Kidney Damage Stage	Description	GFR	Other findings
1	Kidney damage with normal or high GFR	90+	Protein or albumin in urine are high, cells or casts seen in urine
2	Mild decrease in GFR	60-89
3	Moderate decrease in GFR	30-59
4	Severe decrease in GFR	15-29
5	Kidney failure	< 15

 

GFR and EGFR increase during pregnancy.

A measured clearance (GFR) rather than calculated (eGFR) is recommended for:

Persons with known kidney damage (for example as reflected by albumin or protein in the urine)

Patients of extreme age (very old or very young)

Patients of extreme body mass (obese, malnourished, with muscle wasting diseases)

Persons with unusual dietary intakes, including vegetarians

Persons with rapidly changing renal function (includes acute renal disease)

When drug dose adjustments are necessary (persons taking drugs with significant renal toxicity and renal clearance)

The most commonly used equation for calculating the eGFR, and the one recommended by the National Kidney Foundation for general use, is called the MDRD (Modification of Diet in Renal Disease study) equation. The simple version of this equation requires only the serum creatinine, your age and gender. It may be modified depending on your racial origin.