Urea blood test: normal range explained

A urea test measures the amount of urea in your blood. Urea forms when the body breaks down protein, and the kidneys remove it in urine, so a rising level can mean the kidneys are clearing waste less well.

Lab Tests Online UK notes the test is also known as the BUN, or blood urea nitrogen, test, and MedlinePlus describes BUN as the amount of urea nitrogen in your blood. Amara adds, as plain chemistry rather than a quotation: because BUN counts the nitrogen in urea and a urea test counts the whole molecule, the two are printed on different scales, so never swap their ranges.

Doctors order urea as part of a kidney function test, usually with creatinine, to judge how well the kidneys are clearing waste, to follow known kidney disease, and to monitor dialysis. MedlinePlus lists routine check-ups and screening of people at higher risk, such as those with diabetes, high blood pressure, heart disease or a family history of kidney problems. Because urea also rises with dehydration and protein intake, it is read with creatinine rather than alone.

Urea moves with your diet, your fluids and your age, not only with your kidneys.

• A high-protein diet raises urea, and a very low-protein diet lowers it.
• Dehydration, from too little fluid or from vomiting or diarrhoea, pushes urea up without the kidneys changing.
• Urea rises slightly with age and is slightly higher in men than in women.
• Pregnancy lowers urea, especially in the last few months.
• Severe liver disease and malnutrition lower urea, because the liver makes less of it.
• Heart failure, shock, bleeding in the gut, severe burns and a recent heart attack can raise it, which your doctor considers.
• Some medicines that affect the kidneys can raise urea. Tell your doctor what you take.