Blood Urea Nitrogen: What it is & Why is Yours High (or low)

BUN, or Blood Urea Nitrogen, is a test performed on the standard chemistry panel your doctor performs. He or she uses it to rule out kidney disease, but it can be abnormal for other reasons. What does it tell you about your health, function or disease?

Background on BUN

When protein is metabolized, it goes through a few different processes. First it mixes with hydrochloric acid in the stomach and enzymes from the pancreas. This aids the breakdown of large proteins into smaller proteins and amino acids during the process of protein digestion.

At this point a few things can happen. The first thing that occurs, is that the body absorbs the digested protein/aminos. I specifically wrote "protein/aminos" out of a new recognition that the body can absorb larger protein molecules as well as single amino acids. It used to be thought only amino acids could be absorbed.

The body may also NOT absorb protein for a number of reasons leaving it as "food" for bacteria living in the gut. So, not all of the protein and amino acids will be used by the body. Some could be "acted on" by these bacterial colonies. This will become important in a minute.

Once the protein and aminos are absorbed, the liver is responsible for processing them. From here the proteins and amino acids are essentially used as raw materials for the body to make its own proteins. They are disassembled and reassembled according to the body's needs.

You can think of the protein and amino acids as bricks, wood, cement, steel beams, etc that would be brought into a construction site. Those raw materials are then used to construct a building, or house or swimming pool or power plant or highway.

In the body's case, these raw materials are used to make all kinds of things required for detoxification, muscle maintenance and growth, signaling molecules and other processes.

But just as in a construction site, there will be material that is not used that needs to be removed from the site. Things like trash, scrap metal, unused wood, etc.

When protein and aminos are utilized by the body, the "unused material" formed is ammonia. Since ammonia is not a healthy thing to have in high amounts in your body, it is processed by the body into urea.

Urea is then carried in the blood to the kidneys where it is removed and filtered out in the urine. Blood Urea Nitrogen is an indicator of how much ammonia is being transferred into urea.

What can make urea rise?

So now that you have a little background, you may already understand what can make urea rise in the body. Based on what you learned above, here are some possible causes for an elevated BUN:

Excessive protein intake. A diet very high in protein could increase ammonia levels and therefore urea levels. This would be a case of the liver producing urea a bit faster than the kidneys can excrete it. This can be a common thing in bodybuilders and those on very high protein diets for weight loss.

Excessive muscle breakdown. A condition where the body is breaking down muscle protein at a fast rate could cause BUN to go up. Conditions like this might be crash dieting, fasting, excessive exercise, or medical conditions like rhabdomyolysis. Although creatinine is a much better indicator for muscle breakdown compared to BUN. In states of muscle breakdown, BUN may be elevated, but creatinine will be elevated more. This would cause another blood test called the "BUN/creatinine ratio" to go down.

This situation can be further suspected if there are also elevated cortisol levels. Cortisol is catabolic in nature (catabolic means "breaks things down." In this case muscle). By the same token prednisone and other drugs that mimic cortisol can also result in an elevated BUN.

It is not uncommon to see over-trained and heavily exercising athletes who have slightly elevated BUN in and around training times

Dehydration. Dehydration will reduce blood volume and concentrate blood solutes including urea. Therefore, dehydration can be a cause of elevated BUN.

Acute dehydration can be confirmed if you also see high normal or increased hemoglobin (HGB), hemotcrit (HCT), red blood cell count (RBC), sodium and potassium levels

Chronic dehydration will show all of the above plus you may see elevated blood proteins like albumin raised slightly along with BUN.

Digestive dysfunction and dysbiosis. This is the part you will have to follow closely. Remember how I said some protein and amino acids will be used by the bacteria living in your gut? It is useful to remember that there are ten times more bacteria living in your digestive system than there are cells in your body.

Certain of these bacteria (we often refer to them as "bugs") can be your friends because they help in many functions. For example, they help generate vitamins, create beneficial compounds for the immune system, crowd out/suppress infectious bacteria and other things.

But other types of bacteria can be detrimental. They work by crowding out the good bugs, increasing inflammatory triggers (like LPS) and breaking down urea turning it back into ammonia. This ammonia can then gets reabsorbed into the body where the liver has to once again covert it to urea. Can you see how the wrong bacteria growing in your digestive tract can potentially increase ammonia in your body and elevate BUN on a blood test?

These bacteria are more likely to be able to do this if the protein you are eating is inefficiently digested. This is why a high BUN could also signal incomplete protein digestion (mainly caused by low HCL production by the stomach) and/or too many of the wrong types of bacteria populating your gut (called dysbiosis).

If hydrochloric acid is needed, you may also see blood values impacted by low B12 become elevated. This is because B12 absorption relies heavily on HCL production by the stomach. Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin (MCH) also will be high normal to high in this condition. A serum methylmalonic acid test would be best to determine if B12 is adequate or not.

The need for HCL would be more highly suspected if, in addition to a high BUN, you are also experiencing bad breath (not improved by better oral hygiene), increased gas and bloating with high protein foods and/or heart burn and belching. Dysbiosis can also manifest with skin issues and brain fog (ammonia may be a major contributor to brain fog).

Kidney dysfunction or disease. BUN is often the first marker to rise when the kidney function begins to decline and it is also one of the main measures used to track the state of decline in a diseased kidney. If the kidney is involved you will typically see BUN elevated (> 25mg/dl or 8.93mmol/l) along with creatinine (>1.4mg/dl or 123.8umol/dl) and a BUN/creatinine between 10-20. This is why you should always seek a doctors opinion with any blood test result including this one.

Pregnancy. Sometimes pregnancy can show increased BUN levels due to the increased use of protein needed to support mother and baby.

Normal BUN levels?

Your conventional doctor will look at BUN levels strictly to assess kidney disease. He or she is not normally trained in functional medicine and therefore may be unaware of the other potential causes for your increased BUN.

It is essential you follow up with your physician any time you see blood chemistry levels that are out of range as kidney disease is a serious issue.

But as you have learned BUN can be changed in non-disease states. In this case you will want to take action to keep the declining function from leading to a future disease.

The first step in doing this is reading blood labs from a more functional perspective, one where optimal levels are used compared to just disease levels. The truth is, most all of medicine is based on disease values. So, we are not really sure what the optimal levels are. But when you look at healthy individuals around the same age and gender as you it gives you a better understanding.

Based on that factor, here is what we consider optimal for BUN versus a possible disease state:

Optimal values for BUN= 10-16mg/dl (3.57-5.71mmol/L)

Concern levels for BUN= < 5mg/ml or >50mg dl (<1.79 mmol/l or > 17.85 mmol/l

What if levels are low?

Low levels of BUN are a little less common, but if they show up it could be due to any of the following:

  • Low protein diet
  • Malabsorption
  • Pancreatic insufficiency
  • Live disease
  • Some drugs (anabolic steroids & antibiotics)

Some small individuals, with very low muscle mass, can have decreased BUN levels. Petite adult women and children are examples of this.

The Fix

First, don't be dumb. Always check with your doctor regarding any abnormal blood lab to rule out serious disease. In this case the most likely would be kidney.

After that you can address each of the issues I described above making changes and then reassessing.

For excessive protein intake. If your protein intake is much over 45% of your total calorie intake, you may want to decrease it. High protein diets are one of the most effective and proven methods to aid weight loss, but not all metabolic types can handle very high protein levels.

Just realize that we all have different metabolic uniqueness, digestive capacities and varying requirements for protein. If your BUN is slightly elevated and always has been, then perhaps this is normal for you. But it is worth decreasing your protein intake and seeing if levels normalize.

If they do you may want to consider that level your new normal. At this point, instead of using high protein to control hunger, you could increase levels of fiber instead. You can also get more savvy with your protein intake and timing. Some research indicates we may not be able to utilize much more than 40g of protein at a meal. If you are in the habit of eating large protein based meals, or consuming all your protein for the day in one sitting, you may want to consider changing this habit.

For excessive muscle breakdown. If you are an intermittent faster or in the habit of exercising like crazy while taking in little food, you may want to reconsider this approach and see if the change correlates with improved BUN.

It may be a good idea to assess your relationship to stress. There are some biofeedback clues that may help you determine if this is something you may be dealing with. One of them is your level of soreness and recovery from exercise. If you get sore easily or remain sore for long, this may mean you are overdoing it.

Other symptoms of overtraining include sleep changes, low libido, loss of menses (for women), mood changes and lack of motivation for exercise.

For dehydration. It is important to know that the common understanding about how to rehydrate is wrong. Guzzling gallons of water in hopes of hydrating the body can backfire. Hydration is about fluid, electrolytes and the aquaporin receptors on your cells (that let water in), which may be impacted by cell membranes (sterols and fats).

Too much water can drain the body of electrolytes, causing issues like hyponatremia (low sodium in the blood). To be smarter about hydration, use mineral waters when possible and don't over-consume. Drink enough high mineral water to keep your urine a light yellow. Also, contrary to what many will tell you, anything with water can contribute to hydration. So, don't stress that things like coffee and tea are severely dehydrating you, but consider they may be negatively impacting electrolytes if abused. While water should be your preferred hydration method, eating plenty of high water vegetables, fruits, soups and broths can be helpful.

Also, there is a reason Gatorade, Pedialyte and coconut water are so impactful for rehydration. The sugar content actually aids water absorption and utilization. While everyone enjoys a good conspiracy theory, there is actually some good reason to have some glucose in your water for optimal rehydration.

For digestive dysfunction and dysbiosis. You will want to confirm if this is indeed an issue. Is it low HCL and enzyme production or dysbiosis? Chances are it's both, since the former often leads to the latter.

Ask your physician about supplementing with a good quality digestive enzyme that contains HCL and a full spectrum of protein digesting enzymes (protease, trypsin, chymotrypsin, pepsin). The one we sell here at Metabolic Effect is designed for exactly this purpose. GET IT HERE. Take 1-2 with each meal after talking with your doctor.

A good quality probiotic rich in multiple strains of bifidobacterium and lactobacillus species should be taken daily as this can crowd out some of the bacteria that are overproducing ammonia. Some research backing this assessment up can be found here, here and here.

Looking for a way to measure your own blood metabolites without needing a doctor?  Direct Labs allows direct to patient laboratory evaluation.  Check them out if you are concerned with blood lab values.




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