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Urea – Serum Blood Test

Urea is the end product of protein and amino acid metabolism. The urea cycle in the liver converts highly toxic ammonia to urea for excretion with the urine.

Chemical structure of urea.

Standard value:

10–50 mg/dl (1,7–8,3 mmol/l).

Blood urea nitrogen (BUN)

BUN measures the amount of urea nitrogen found in blood. BUN is easily calculated from the urea concentration: multiply urea in mg/dl with 0,467. The urea concentration and BUN in mmol/l are identical.

Laboratory test method:

Spectrophotometry.

Indications:

Estimation of protein metabolism (anabolic, catabolic). Acute renal failure and chronic kidney disease. The routine measurement of creatinine and urea is often unnecessary. With relatively good renal function, the urea concentration is subject to higher fluctuations compared to creatinine and is therefore not helpful as a kidney function parameter. In preterminal renal insufficiency, however, the urea concentration is helpful to assess residual kidney function.

Differential Diagnosis of Elevated Urea

• Acute kidney injury and chronic renal insufficiency.
• Nonrenal causes of elevated urea concentrations are exsiccosis, high-protein diet and catabolic metabolic situations such as trauma, fever and hunger.

Differential Diagnosis of Low Urea

Malnutrition, hepatic insufficiency.

References

  Deutsche Version: Harnstoff Laborwert