As a Registered Dietitian (RD), who specializes in kidney nutrition for Polycystic Kidney Disease, I want to clear up the confusion between BUN (Blood Urea Nitrogen) and creatinine. Understanding the differences, and similarities, between these two labs can help you better manage your kidney health and guide dietary choices.
Similarities Between BUN and Creatinine
Before diving into their differences, it's important to understand how BUN and creatinine are similar. Both measure waste products in your blood and are part of a standard kidney panel, which your doctor orders to look at your kidney function.
Each has a "normal range" listed on the lab results. This reflects the amounts of urea nitrogen and creatinine waste found in the blood when your kidneys are working at full function. Levels above this "normal range" can indicate kidney injury or damage. With any kidney injury or loss of function, both lab results often go above the normal range because the kidneys aren't able to fully filter out all the waste.
With PKD, monitoring BUN and creatinine levels helps evaluate how well your kidneys are working at filtering waste. However, elevated levels don't always mean your function has declined or there is a kidney issue. Various factors outside of your current kidney function, including diet and hydration, can impact the lab results.
That's why it's important to consider what was happening at the time of your lab tests and look at trends over time. If you are looking for an easy way to monitor your labs, download my free Track & Trend Your PKD Labs Tool.
Differences Between BUN and Creatinine
Now, let's get into how BUN and creatinine waste, and labs, are different.
BUN (Blood Urea Nitrogen)
- Reference Range: 7 to 20 mg/dL *You'll find slightly different ranges depending on where your labs were drawn.
- Where it comes from: BUN measures urea nitrogen waste in the blood. The main source of urea nitrogen in your diet is animal protein. When animal protein is metabolized, broken down, it generates urea nitrogen as waste. This is just one reason why a lower protein diet is recommended for PKD'ers with a lower eGFR, a lower kidney function. Less protein in means less waste for the kidneys to have to filter (or not)!
- Non-kidney factors that can affect levels: Several things that can lead to an increased BUN lab result are a high protein diet, dehydration, infection, pregnancy, and certain medications like steroids.
- Fun Fact: BUN used to be used to estimate kidney function. Because there are many factors outside of the kidneys that can affect levels it is no longer used!
Creatinine
- Reference Range: 0.7 to 1.3 mg/dL *You'll find slightly different ranges depending on where your labs were drawn.
- Where it comes from: Creatinine is a waste product of normal muscle activity. Normal muscle and movement wear and tear. Creatinine is also generated from the breakdown of dietary protein, primarily animal-based proteins. Almost all creatinine waste is filtered by your kidneys and excreted in urine.
- Non-Kidney factors that can affect levels: several things that can lead to an increased creatinine lab value are being very muscular, consuming heavy dietary protein amounts, supplements, and exercising before labs.
- Fun Fact: Creatinine is used to calculate your glomerular filtration rate (eGFR), an estimate of kidney function. Your creatinine level, along with age and sex, is used in the equation. Because of this, different folks can have the same creatinine level but different eGFR values.
In Summary
BUN and creatinine are both waste measures used to assess kidney function. Creatinine is less influenced by factors outside of your kidneys and is used to calculate eGFR. Both markers can be influenced by diet, particularly when kidney function is reduced. Remember, more waste equals more work for your kidneys. With PKD, it's important not to overburden your kidneys by consuming excessive protein, especially from animal sources.
By understanding the roles of BUN and creatinine, you can better manage your kidney health and make informed dietary choices. Feel free to share your thoughts or questions in the comments below.
More Insight Into Your PKD Labs
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Stay informed, stay healthy, and take control of your PKD management journey!
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