How do we measure kidney function?

The kidney has many functions as it removes waste, maintains fluid and electrolyte balance, and regulates body pH. The GFR, or glomerular filtration rate, measures the total for filtration rate of the 1 million nephrons in each kidney. Unfortunately, it’s difficult to detect early loss of kidney function from GFR alone because it often remains unaffected at this stage. Patients also may not show any symptoms. So how do we measure kidney function? Thankfully, there are other markers that can flag problems early.

How do we measure kidney function?


Markers of Kidney Function

Blood Creatinine Level:  Creatinine is a breakdown product of creatine which comes from our muscle. It varies among all of us.  Younger people, men, and African American people typically have higher muscle mass and higher blood creatinine level compared to other demographics. Decreased muscle mass can also lower creatinine levels, such as in patients with malnutrition, amputees, and people at an advanced age.

Right now, the blood creatinine level is the most extensively used measure of kidney function. These measurements are not directly correlated with GFR, which is only an estimate.

Cystatin C: This marker is produced by all cells with a nucleus and it is less affected by sex, age, or muscle mass than blood creatinine level. It may be affected by any ongoing diseases such as malignancy, HIV, or inflammation of the body. However cystatin C is a better detector of small changes in kidney function than blood creatinine level. High levels of this protein indicate that there may be issues.

How to Estimate GFR

GFR can be calculated using a formula. That equation uses your age, sex, race, and blood creatinine level to give an estimate of your glomerular filtration rate.

It’s possible to obtain a more accurate measurement by using a 24-hour urine collection. This method is not recommended for routine use. The gold standard for measurement of GFR is a radionucleotide imaging study. We use this for accurate determination of GFR during the evaluation of kidney donors and kidney recipients.


If you’re seeking a nephrologist for kidney-related problems, Dr. Gandotra’s offices are located in Orange County, California. If you’d like to book an appointment today, call Dr. G’s office phone: (714) 435-0150