How is kidney function measured?

Kidney function is measured using a combination of blood tests, urine tests, and sometimes imaging studies. These tests help show how well your kidneys are doing their job of filtering waste, balancing fluids, and regulating important chemicals in the body.

One of the most common tests is the estimated glomerular filtration rate (eGFR). This number is calculated from your creatinine level—a waste product found in the blood—along with your age, sex, and body size. The eGFR gives a rough estimate of how much blood your kidneys filter per minute. A normal eGFR is usually above 90 mL/min, and lower numbers may indicate reduced kidney function.

Another key test is the blood urea nitrogen (BUN) level. Urea is another waste product filtered by the kidneys. If the BUN level is higher than normal, it may suggest your kidneys are not clearing waste as effectively as they should.

Urine tests are also used to assess kidney health. A urinalysis checks for things like protein, blood, or glucose in the urine—all of which may signal early kidney problems. A urine albumin-to-creatinine ratio (ACR) is more specific and measures how much protein is leaking into the urine, which can be an early sign of kidney damage.

In some cases, doctors may order an ultrasound or CT scan to look at the size and structure of the kidneys, especially if blockages, cysts, or stones are suspected.

Together, these tests provide a clear picture of how well your kidneys are working. Even if you feel fine, regular testing can detect early changes before symptoms appear, which is especially important for people with high blood pressure, diabetes, or a family history of kidney problems.

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