Dr. med. Dirk Manski

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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.

figure chemical structure of urea

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:



Estimation of protein metabolism (anabolic, catabolic). Renal insufficiency. The routine measurement of creatinine and urea is often not necessary. 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

Differential Diagnosis of Low Urea

Malnutrition, hepatic insufficiency.

Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Guder, W. G. & Nolte, J.
Das Laborbuch für Klinik und Praxis
Urban + Fischer, 2009

Siegenthaler 1988 SIEGENTHALER, W. ; SIEGENTHALER, W. (Hrsg.):
Differentialdiagnose innerer Krankheiten.
Georg Thieme Verlag, Stuttgart, New York., 1988

  Deutsche Version: Harnstoff Laborwert