June 25, 2020
What is Urea?
Urea is generated by our body following breakdown of protein in the liver. It is then released to the bloodstream and removed from the body by the kidneys. When our kidneys are not working properly, they will not be able to remove as much urea from the blood as they normally would, and the urea level in the blood will increase. However increased urea levels can also be due to increased production of urea, which can be caused by for example a diet with high amounts of protein.Historically, measurement of urea levels in the blood and urine has been crucial for the evaluation of kidney function. Although newer markers of kidney function such as Creatinine and Cystatin C are now gaining more popularity in the clinic, the urea test remains an important component of kidney function assessment.
Why is this analysis important?
Urea levels in the blood can be determined as a part of a general health check to assess kidney function, i.e. how efficiently our kidneys remove waste from our body. Doctors may also order a urea test if they suspect problems with kidney function or to follow the disease progression in patients with chronic kidney problems. Loss of kidney function does not usually lead to any symptoms in the early stage. Even at a later stage, the symptoms can be very unspecific, and appear in forms such as fatigue or swollenness. A blood test is therefore needed.
In short, it is useful to analyse urea levels in the blood to:
Assess kidney function
Monitor the progression of kidney disease
The reference ranges for urea levels in the blood can be different depending on your age and the laboratory and technique used. Doctors usually also take into account a number of factors when evaluating urea values.
High urea levels in the blood may be associated with:
Acute or chronic kidney failure
Tissue damage, as in trauma
Glucocorticoid treatment (such as Prednisone)
Low urea levels in the blood may be associated with:
Low protein diet
Urea levels in the blood are affected by the amount of protein contained in the diet. As the protein intake can vary from meal to meal and person to person, urea levels in the blood can also fluctuate. Due to these uncertainties, a urea test alone is often not sufficient to confirm or rule out problems with kidney function. It is therefore common to evaluate urea levels in the blood together with other markers of kidney function such as the Estimated Glomerular Filtration Rate (eGFR), Creatinine and Cystatin C.
Assessment of kidney function. Lesley A Inker, MD, MS. UpToDate Jun 12, 2018