Urea in your blood: what a high or low value means

Urea is one of those values you see on your result without quite knowing what to do with it. It is often measured with creatinine, but it behaves differently. Urea reacts strongly to what you eat and drink, which makes it more nuanced than many people think (Weiner 2015).

This article expands on the overview about your kidney function, focusing on urea.

What is urea?

Urea is a waste product formed when your body breaks down protein. Nitrogen is released, your liver turns it into urea, and your kidneys filter it out. Because your kidneys excrete urea, the value partly reflects kidney function. Abroad you often see the term BUN, blood urea nitrogen, which measures essentially the same thing expressed as nitrogen.

What does a high urea mean?

A raised urea can point to reduced kidney function, but not always. It also rises with dehydration and a high-protein diet. Imagine someone who drank too little on warm days and ate a lot of meat: their urea can be high with nothing wrong with the kidneys. That is why a doctor never reads urea alone, but alongside creatinine and eGFR.

What does a low urea mean?

A low urea gets less attention but does occur. It can fit a low-protein diet, drinking a lot, or sometimes a liver problem, since the liver makes urea. A mildly low value is usually no cause for concern.

High and low urea at a glance

To see how urea relates to the other kidney values, read on about high creatinine and eGFR explained.

Why urea and creatinine are read together

Both are waste products your kidneys excrete, but they react differently. Creatinine is more stable and depends on muscle mass, while urea moves more with fluid and protein intake. If only urea is raised while creatinine is normal, that points more often to dehydration or diet than to the kidneys. See also urea.

What can you do?

To map your kidney values, you can have a kidney function test at Vitalcheck without a referral, capturing urea, creatinine and eGFR at once. Drink normally in the days before the draw and note whether you ate a lot of protein beforehand.

References

• Weiner ID, et al. Urea and Ammonia Metabolism and the Control of Renal Nitrogen Excretion. Clin J Am Soc Nephrol. 2015. PMID: 25078422.
• Webster AC, et al. Chronic Kidney Disease. Lancet. 2017. PMID: 27887750.
• Nierstichting. How your kidneys work.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.