Why Your Kidney Function Tests Look Different After Age 65

It’s no secret that your body naturally changes as you age, and the kidneys are no exception. After age 65, these changes affect the results of kidney function tests, making it appear like you have kidney disease even when you don’t.

Unfortunately, these test results can lead to a misdiagnosis if age-related changes aren’t considered.

At Deon D. Middlebrook MDPC, we’re experts in the variables affecting your kidney health and kidney function tests, including the impact of aging. 

Here, we explain two essential kidney function tests and why they change with age.

About kidney function tests

Kidney function tests measure the levels of certain substances in your blood and urine that indicate how well your kidneys are working.

While numerous tests can be used to evaluate kidney health, two in particular provide a clear overview of kidney function and are often used for early detection of kidney disease. Both tests change with age.

Estimated glomerular filtration rate (eGFR)

The eGFR indicates kidney function and the stage of your kidney disease based on blood levels of creatinine. Creatinine is a waste product that’s produced during muscle metabolism.

Healthy kidneys filter creatinine, removing it from the bloodstream and eliminating it through urine. If creatinine remains in your blood, it’s a sign that the kidneys aren’t doing their job.

A formula is used to calculate the eGFR, taking into account your creatinine levels, age, gender, and body size. High creatinine levels reflect poor kidney function. 

However, the eGFR indicates the severity of the problem. As a result, a low eGFR is a sign of kidney disease. The lower the eGFR, the worse the kidneys are working.

Urine albumin-creatinine ratio (uACR)

The uACR measures the amount of albumin (a protein in your blood) and creatinine. Healthy kidneys filter out creatinine while keeping albumin in your blood. Damaged kidneys will allow albumin to leave the bloodstream and enter your urine.

Comparing the amount of albumin to creatinine in your urine reveals kidney function and early signs of kidney damage.

Effect of aging on kidney function tests

After age 65, natural changes occur in your body that affect the results of eGFR and uACR tests. These are the two most influential changes:

Kidney function

Nephrons are tiny structures inside your kidneys that are responsible for filtering blood to remove wastes, eliminating wastes through urine, and sending essential substances back into circulation.

As you get older, you lose some nephrons. Additionally, the remaining nephrons slow down and may not work as well. This decline in kidney function doesn’t mean you have kidney disease.

However, these changes affect the eGFR. After 65, your normal eGFR rate will be low, even when your kidneys are healthy. Having a low eGFR after 65 may lead to a misdiagnosis of kidney disease if your healthcare provider doesn’t take your age into account.

Muscle mass

Most people lose muscle mass as they age. The process can begin in your 30s, but it accelerates significantly after age 60.

Since creatinine is produced when muscles are active, the loss of muscle mass affects its levels. This decline in creatinine may mask kidney disease because higher-than-normal levels won’t appear in your blood during an eGFR test. 

Expert kidney assessment at every age

Call Deon D. Middlebrook MDPC today or request an appointment online for expert kidney care, including an accurate assessment, diagnosis, and treatment tailored to meet your unique needs.