To Determine Urea Clearance
17
17.1 Theory
To assess the kidney functions, clearance of some of the substances from the kidneys
is measured. The clearance of substances that arefiltered exclusively or predomi-
nantly by the glomeruli but neither reabsorbed nor secreted by other regions of the
nephron can be used to measure glomerularfiltration rate (GFR). The concept of
urea clearance was introduced by Van Slyke and his coworkers in 1928. Urea
clearance (C) is defined as volume of blood or plasma completely cleared of urea/
min by the kidneys and can be expressed mathematically as
C¼UV=PU¼concentration of urea in urine/dl
P¼concentration of urea in plasma/dl
V¼volume of urine excreted/min
17.2 Maximum Urea Clearance
If the volume of urine excreted/min is more than 2 ml/min, maximum urea clearance
is calculated, and the observed maximum clearance can be compared with the
average normal value of 75 ml/min.
Maximum urea clearanceð%average normalÞ¼observed clearance 100
75
¼ 1 : 33 UV=P#Springer Nature Singapore Pte Ltd. 2018
V. Kumar, K. D. Gill,Basic Concepts in Clinical Biochemistry: A Practical Guide,
https://doi.org/10.1007/978-981-10-8186-6_17
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