A Primer on Basic Kidney Function Labs

Each visit with your nephrologist results in lab tests to measure your kidney function—eGFR, mGFR, BUN, and uACR. Huh? Let’s demystify these hieroglyphics so you can feel more empowered to understand your lab results.

The key to understanding your kidney function labs is remembering that your kidneys’ primary task is to filter waste and excess fluid from your body through urine.

Blood Urea Nitrogen (BUN) measures the level of urea nitrogen (a waste product) in your blood. An elevated level of BUN may indicate your kidneys are not performing well. However, a high BUN level is not a stand-alone indicator of kidney failure. This lab value must be interpreted in conjunction with other lab values. Normal results depend on age and gender, but generally considered to be Results should be generally between 6-24 mg/dl.

Creatinine (Cr): Like BUN, creatinine is another waste product filtered by your kidneys. Elevated creatinine combined with elevated BUN may mean a kidney problem. Normal creatinine levels for men are 0.7 – 1.3 mg/dl. For women, normal levels are 0.6 – 1.1 mg/dl.

BUN/Creatinine ratio: Dividing your BUN level by your creatinine level equals your BUN/Cr ratio. The results of this test help your doctor determine the cause of your kidney disease and whether it is acute or chronic. This ratio will be interpreted in conjunction with the results of your BUN and creatinine levels. A typical result should be between 10:1 and 20:1.

Glomerular Filtration Rate (GFR) – This is not exactly a lab test; GFR is calculated using your creatinine level, age, and gender. Because this value is based on a formula, the result is estimated (eGFR). A measured (mGFR) is more accurate but also more time-consuming, expensive, and not as readily available. eGFR of 90 or higher is considered normal. eGFR is a measure of the severity of kidney damage, as the disease progresses eGFR will decrease.

Urine albumin-creatinine ratio (uACR): This is a test to determine if albumin is present in your urine. Albumin is a protein that should be in your blood. Damaged kidneys allow this protein to “spill” into your urine. A normal amount of albumin is 30 mg/g. Results above this may indicate kidney damage.

Lab test results are just one aspect of assessing kidney disease. A diagnosis cannot be made by looking at any one lab result independently. A thorough assessment of the severity of kidney disease depends on your provider’s review of your medical history and symptoms.

Dana Cook, RN, LCSW

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