Serum Urea
Urea is formed by the urea cycle in the liver from
ammonia (produced mainly from amino acid catabolism) &
excreted mainly by the kidney through glomerular filtration
& to less extent through the skin or GIT.
Serum urea level is elevated by six main causes:
1- Reduction of Glomerular Filtration Rate (GFR).
2- Sustained very high protein diet because of the
elevation in the amino acid available for catabolism & so
for urea synthesis.
3- Drugs as diuretics (because of the increase in the
tubular reabsorption of urea) & steroids (because of the
increase in the amino acids catabolism).
4- Hypercatabolic state as in very severe trauma & heart
failure because of the increase in the amino acids
catabolism.
5- Dehydration because of the increase in tubular
reabsorption of urea.
6- Old age group.
Therefore; the main limitation of serum urea result is that it
is not specific for glomerular impairment.
Reference range of serum urea: = 2.5-7.5 mmol/L (15-
45 mg/dL) Note: To convert from mmol/L into mg/dL ×6
Conditions associated with low serum urea:
1- Overhydration as in pregnancy or I.V. fluid infusion
because of the reduction in the tubular reabsorption of
urea.
2- Severe liver diseases because of urea cycle
impairment.
3- Starvation or malabsorption because of the reduction in
the amino acid available for catabolism & so for urea
synthesis.
4- Infant: because of immaturity of urea cycle enzymes.
:
of measurement
Principle
Enzymatic colorimetric measurement of urea depends on hydrolysis
of serum urea by urease enzyme into ammonium ions & carbon
dioxide, then ammonium ions in alkaline media forms with salicylate &
chloride a green colored complex (indophenol) that measured at
wavelength 600 nm.
د. بسام ادور/كلية طب نينوى