Urea is the final degradation product of protein and amino acid metabolism. In protein catabolism the proteins are broken down to amino acids and deaminated. The ammonia formed in this process is synthesized to urea in the liver. This is the most important catabolic pathway for eliminating excess nitrogen in the human body.
Urea is synthesised in the liver as the nal product of protein and amino acid metabolism. Urea synthesis is therefore dependant on daily protein intake and endogenous protein metabolism. Most of the urea produced during these metabolic processes is eliminated by glomerular ltration, with 40 – 60% diffusing back into the blood, irrespective of the ow rate in the proximal tubule. Rediffusion in the distal tubule depends on the urinary ow and is regulated by antidiuretic hormone. During diuresis, there is minimal rediffusion of urea into the blood; a large quantity of urea is excreted in the urine and plasma urea concentration is low.
During antidiuresis, which may occur in oliguric heart failure, exsiccosis or thirst, urea rediffuses in the tubules at an increased rate and plasma urea is increased. In pre- and post renal kidney failure, the tubular urine ow is decreased, resulting in increased rediffusion of urea in the distal tubules and increased creatinine secretion. Prerenal elevation of urea occurs in cardiac decompensation, increased protein catabolism and water depletion. Urea levels may be elevated due to renal causes such as acute glomerulonephritis, chronic nephritis, polycystic kidney, tubular necrosis and nephrosclerosis. Post renal elevation of urea may be caused by obstruction of the urinary tract.
Plasma urea concentration is determined by renal perfusion, urea synthesis rate, and glomerular ltration rate (GFR) and may be increased in acute renal failure, chronic renal failure and prerenal azotaemia. In dialysis patients the urea concentration is representative of protein degradation and is also an indicator of metabolic status. In end-stage renal failure, the urotoxic signs, in particular those relating to the gastrointestinal system, correlate well with urea concentration. Instructions Serum urea and serum creatinine determinations are frequently performed together in the differential diagnosis of kidney function.
REFERENCE INTERVALS - Urea Serum/plasma (reference range according Tietz) Adult (18‐60 years) 2.14‐7.14 mmol/L (12.9‐42.8 mg/dL) Adult (60‐90 years) 2.86‐8.21 mmol/L (17.1‐49.3 mg/dL) Infant (< 1 year) 1.43‐6.78 mmol/L (8.6‐40.7 mg/dL) Infant/child 1.79‐6.43 mmol/L (10.7‐38.6 mg/dL)
SI units Conversion Calculator. Convert Urea level to mmol/L, µmol/L, mg/dL, mg/100mL, mg%, mg/L, µg/mL . Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Urea unit conversion to mmol/L, µmol/L, mg/dL, mg/100mL, mg%, mg/L, µg/mL .