Urea in Blood: Reference Values, Ureic Nitrogen Test, and Effects of High and Low Levels on the Body

It is a waste product of many living organisms and is the leading organic component of human urine.

This is because it is at the end of the chain of reactions that break down the amino acids that makeup proteins. These amino acids are metabolized and converted to ammonia, CO², water, and energy in the liver.

But ammonia is toxic to cells, so it must be excreted from the body. Aquatic creatures, such as fish, can expel ammonia directly into the water, but land animals and humans need another disposal method.

The liver then converts the ammonia into a non-toxic compound, urea, which can then be safely transported in the blood to the kidneys, where it is eliminated in the urine.

What are the reference values?

The reference values ​​for urea in adults range from 15:45 mg/dl, while the reference value is between 05:18 mg/dl in children.

High urea can signify that the kidneys are not working correctly. However, urea levels are not very reliable for verifying kidney function since its elevation is often related to the diet and the person’s hydration status.

Urea is a consequence of the metabolization of proteins ingested in the diet, produced by the liver, and eliminated by the kidneys through the urine. When the kidneys lose their ability to filter the blood properly, urea accumulates in the bloodstream, and its values ​​are high.


In kidney failure, urea levels in the blood are always high. However, high urea levels do not always mean problems in the kidneys because its values ​​can be changed in cases of a diet rich in protein, dehydration, heart attack, infections, tumors, and liver diseases, among other situations.

And a low level can be related to malnutrition, lack of protein in the diet, liver failure, pregnancy, and celiac disease, among other conditions.

Blood urea nitrogen test

The blood urea nitrogen test measures how much waste product you have in your blood. If your levels are outside the normal range, this could mean that your kidneys or liver may not work correctly.

Test indications

Your doctor may order a test as part of a routine checkup. It can be one of several blood tests you get.

If you have a kidney condition, the test is a way to check your urea levels before starting a drug or treatment.

Causes of high blood urea levels

  • High protein diet.
  • Fever or infection increases the breakdown of proteins. Increased protein breakdown is a common feature of the disease.
  • Inflammation or interval training results in the breakdown of muscle proteins.
  • Dehydration or low water consumption.
  • Stress.
  • Intestinal bleeding When upper gastrointestinal bleeding occurs, the blood is digested into protein. This protein is transported to the liver and metabolized.
  • Poor circulation results in lower blood flow to the kidneys and, therefore, a decreased ability to remove urea.
  • Thyroid abnormalities cause abnormal kidney function, such as hypothyroidism and hyperthyroidism.
  • Glucocorticoids, tetracyclines (except doxycycline), and other anabolic drugs.
  • Kidney disease or failure and blockage of the urinary tract from a kidney stone.

Why is a high blood urea level terrible?

Elevated urea alone has some adverse effects. Urea in high concentrations can cause oxidative stress in cells.

However, a high urea level is also an indicator of other underlying conditions.

Indicates increased protein degradation, which is associated with decreased immune function. One study shows that patients with elevated urea levels (> 20 mg/dl) are at increased risk of infection.

It is also associated with higher mortality in critically ill patients.

Elevated urea is also associated with an increased risk of stroke in cardiac surgery and adverse outcomes in atherosclerosis and heart failure patients.

Symptoms of a high urea level

The urea nitrogen test is often ordered for people experiencing signs and symptoms of kidney disorders. These symptoms can include:

  • Frequent urination
  • Discolored urine (bloody, dark, or foamy).
  • Joint pain
  • Bone-ache.
  • Back pain.
  • Muscle cramps.
  • Restless legs.
  • Fatigue.
  • Trouble sleeping
  • Poor appetite
  • Swelling (especially in the extremities)
  • Itch.

Causes of low blood urea levels

  • Low protein diet, malnutrition, or starvation.
  • I have impaired liver activity due to liver disease.
  • Genetic deficiency of the enzymes of the urea cycle.
  • Anabolic steroids decrease protein breakdown.
  • Overhydration or drinking a lot of water.
  • Pregnancy (due to increased plasma volume).

How do lower the levels of urea in the blood?

There are two main ways:

  • Drink more water.
  • Eat less protein.

Ginger can help with the removal of urea from the blood.

Interesting Facts About Urea

  • Urea is a diuretic that causes us to lose water.
  • Urea creams promote skin rehydration.
  • Urea is the main ingredient in urine, sometimes used in alternative medicine.