Testing urea levels in blood provides information about your health. This post covers the causes of high and low blood urea nitrogen (BUN) and what they may mean for you.
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- What is Blood Urea Nitrogen (BUN)?
- BUN Blood Tests
- Why is the BUN Test Given
- Optimal and Normal BUN Range in Blood Test
- Factors that Elevate BUN
- Why is High BUN Bad?
- Symptoms of High Urea Nitrogen/BUN
- BUN to Creatinine ratio (BUN:creatinine)
- Factors that Decrease BUN
- How to Decrease or Reduce BUN
- Interesting Facts About Urea
- Genetics of Urea
- Irregular BUN levels?
What is Blood Urea Nitrogen (BUN)?
Blood urea nitrogen (BUN) is a measure of the amount of urea in the blood (R). It provides useful information about your health.
Urea is derived from dietary protein and tissue protein turnover (R).
On a normal diet, we produce about 12 g of urea each day (R).
The bulk of the urea, about 10 g each day, is eliminated by the kidneys (R).
BUN levels represent the balance between urea production (liver), urea breakdown and urea elimination (kidneys) (R). Therefore, BUN is an indicator of kidney health and/or liver health.
However, when it comes to kidney function, creatinine is a much more reliable indicator than the BUN, because the BUN is far more likely to be affected by dietary and physiologic conditions not related to kidney function (R).
BUN Blood Tests
Any standard blood test will have BUN or urea numbers. Conventional doctors will look at high or low BUN numbers and not mention anything, but these can indicate that certain processes in the body aren’t optimal.
Why is the BUN Test Given
A blood urea nitrogen (BUN) test is done to:
- See if your kidneys are working normally or if kidney disease is progressing
- Check for severe dehydration
Optimal and Normal BUN Range in Blood Test
The BUN is roughly one-half of the blood urea (R).
Normal human adult blood should contain between 5 to 20 mg of urea nitrogen per 100 ml (5–20 mg/dL) of blood, or 1.8 to 7.1 mmol urea per liter (R).
To convert from mg/dL of blood urea nitrogen to mmol/L of urea, multiply by 0.357.
The range is wide because of normal variations due to protein intake, protein break-down, state of hydration, liver urea production and urea elimination by the kidneys (R).
Factors that Elevate BUN
- High protein diet (R).
- Fever or Infection, which increase protein breakdown (R). Increased protein breakdown is a common feature of illness. Protein breakdown is stimulated by hormones (such as glucagon, epinephrine, cortisol) and inflammatory cytokines. Protein production on the other hand, is reduced by lowering growth hormone, insulin, and testosterone levels (R).
- Inflammation or interval training, which results in protein breakdown from muscle.
- Dehydration or low water consumption – I use this as a measure of hydration in clients. BUN increases as blood volume decreases (R).
- Stress. An inappropriate increase in the activation of the sympathetic, renin–angiotensin–aldosterone, and arginine–vasopressin systems elevate BUN (R), which often seen in heart failure (R). Cortisol will also increase protein breakdown and elevate BUN.
- Gut bleeding (R). When upper GI bleeding occurs, the blood is digested to protein. This protein is transported to the liver, and metabolized to BUN (R).
- Poor circulation, which results in lower blood flow to the kidneys and therefore less of an ability to clear the urea (R, R).
- Thyroid abnormalities which result in abnormal kidney function: hypothyroidism (R) and hyperthyroidism (R).
- Glucocorticoids, Tetracyclines (except doxycycline) and other antianabolic drugs (R).
- Lower growth hormone or IGF-1. IGF-1 and growth hormone inhibit urea synthesis (R).
- Kidney disease or failure, and blockage of the urinary tract by a kidney stone (R).
Why is High BUN Bad?
However, high BUN is also an indicator of other underlying conditions.
High BUN indicates increased protein breakdown, which is associated with decreased immune function. A study shows that patients with elevated BUN (> 20 mg/dl) have an increased risk of infection (R).
Note that BUN values remain within the normal range until more than 50% of renal function is lost. Within that range, however, a doubling of the values (e.g., BUN rising from 8 to 16 mg/dl) may mean a 50% fall in kidney function (R).
Symptoms of High Urea Nitrogen/BUN
The urea nitrogen test is often ordered for people who are experiencing signs and symptoms of kidney disorders. These symptoms can include:
- Frequent urination
- Discolored urine (bloody, dark, or foamy)
- Joint pain
- Bone pain
- Back pain
- Muscle cramping
- Restless legs
- Trouble sleeping
- Poor appetite
- Swelling (especially in the extremities)
BUN to Creatinine ratio (BUN:creatinine)
A BUN test is usually done with a blood creatinine test.
The level of creatinine in your blood also tells how well your kidneys are working. A high creatinine level may mean your kidneys are not working properly, but if it’s slightly elevated, it could simply mean that you have a lot of muscle.
Blood urea nitrogen (BUN) and creatinine tests can be used together to find the BUN-to-creatinine ratio.
In general, you want to have lower BUN and lower creatinine. However, in most cases, it’s healthier to have a lower ratio of BUN to creatinine (10 is ideal).
Factors that Decrease BUN
- Low-protein diet, malnutrition or starvation (R).
- Impaired liver activity due to liver disease (R).
- Genetic deficiency of urea cycle enzymes (R).
- Higher IGF-1 and growth hormone. These inhibit urea synthesis (R). Growth hormone-deficient children given human growth hormone have lower urea nitrogen and this is due to decreased urea synthesis (R).
- Anabolic steroids, which decreases protein breakdown.
- Overhydration, or drinking a lot of water.
- Pregnancy (due to increased plasma volume) (R).
How to Decrease or Reduce BUN
There are two main ways to decrease BUN:
- Drink more water
- Eat less protein
Arginase converts L-Arginine to Urea. When you inhibit arginase, you decrease urea. The downside to this might theoretically be a buildup of ammonia.
The following inhibit arginase:
Interesting Facts About Urea
Urea creams promote rehydration of the skin (R).
Urea is the main ingredient in urine, which is sometimes used in alternative medicine.
Genetics of Urea
There are five key enzymes in the urea cycle: carbamoyl-phosphate synthetase 1 (CPS1), ornithine transcarbamylase (OTC), argininosuccinate synthetase (ASS1), argininosuccinate lyase (ASL), and arginase 1 (ARG1). Additionally, a sixth enzyme, N-acetylglutamate synthase (NAGS), is critical for urea cycle function, providing CPS1 with its necessary cofactor. Deficiencies in any of these enzymes result in elevated blood ammonia concentrations, which can have detrimental effects, including central nervous system dysfunction, brain damage, coma, and death (R).
Two SNPs -389 G/A (rs5963409) and -241 A/G (rs5963411) in the OTC gene are associated with the risk of developing Alzheimer’s (R).
SNPs in the ARG2 gene
rs742869 (G) a minor allele is associated (in men) with an increase in Alzheimer’s disease risk, an earlier age at onset and a potential decrease in Arg2 expression (R).
Irregular BUN levels?
Are your issues with the urea cycle are caused by your genes? Upload your genetic data to SelfDecode to find out. SelfDecode is the best and most powerful genetic application, which will help you interpret your genes. You need to sign up and upload your genetics to see what versions of these genes you have (using 23andme or ancestry).
Here are relevant SelfDecode pages:
- Urea Cycle
- Urea Transport
- Urea Channel Activity
- Urea Metabolic Process
- Urea Cycle Disorders (Inborn)
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