Creatinine is a waste product generated by everyday muscle metabolism. Normally, your kidneys filter creatinine from your blood and send it on to be excreted in your urine. When your kidneys aren’t functioning correctly, creatinine can build up in your bloodstream. A serum creatinine test measures how much creatinine is in your blood, which in turn gives your doctor an idea of how well your kidneys are doing their job.* 

Does a high creatinine level mean my kidneys aren’t working?

While a high level of serum creatinine does suggest that your kidneys are not functioning optimally, the creatinine level in your blood can also be affected by several other factors, including:

• Age
• Race
• Gender (men generally have higher creatinine levels than women)
• Body size
• Diet (particularly one high in red meat)
• Dehydration
• Blood volume
• Medications and dietary supplements

If your blood creatinine is high, your doctor may order subsequent blood creatinine tests, spaced out over time, to see if the level continues to increase. They may also order other tests to get a broader and more accurate picture of how your kidneys are functioning. 

What other tests might be ordered?

Since a serum creatinine test alone is unable to accurately determine the extent of kidney function, other tests are necessary to:

• Establish kidney health status
• Diagnose kidney disease
• Evaluate disease progression risk
• Inform treatment

The three common tests administered for these purposes are:

• Glomerular filtration rate (GFR)
• Creatinine clearance
• Albumin-to-creatinine ratio (ACR)

Glomerular filtration rate

Your glomerular filtration rate is a computation that estimates the percentage of kidney function you currently have. This measurement is part of your routine blood work and can be found on your lab report. 

If your GFR is 60, that means that your kidneys are working at 60%. If your GFR is below 60, or if it is above 60 but is accompanied by other indications of kidney damage, you may have kidney disease.

Creatinine clearance

The creatinine clearance test measures the amount of creatinine that has filtered through your kidneys into your urine. The test is not part of a routine lab workup and requires that you collect the urine you excrete for a specific amount of time, typically a period of 24 hours. Like the blood creatinine test, creatinine clearance shows how efficiently your kidneys remove waste.

Albumin-to-creatinine ratio

Albumin is a normal protein that your body produces. Healthy kidneys will allow only a tiny amount of albumin to leave your bloodstream and enter your urine. An albumin-to-creatinine ratio test is a urine test that requires approximately two tablespoons of urine for analysis. If more than 30 mg/g of albumin are present in your urine, you might have kidney disease, even with a GFR greater than 60.

If you have other conditions, such as diabetes and/or high blood pressure, that can affect your kidneys or if you already have a kidney disease diagnosis, your doctor may order serum creatinine or other tests multiple times to monitor your kidney health status.

*Mayo Clinic. (2018, Dec. 22). Creatinine Test. https://www.mayoclinic.org/tests-procedures/creatinine-test/about/pac-20384646