The diacetyl, or Fearon, reaction develops a yellow chromogen with urea, and this is quantified by photometry.
There are two general methods for the measurement of urea nitrogen. Most of those in current use are automated and give clinically reliable and reproducible results. Multiple methods for analysis of BUN and creatinine have evolved over the years. For the adult female, with her generally lower muscle mass, the normal range is 0.5 to 1.1 mg/dl, or 44 to 97 μmol/L by the enzymatic method.
#ELEVATED CREATININE NORMAL BUN MANUAL#
For the adult male, the normal range is 0.6 to 1.2 mg/dl, or 53 to 106 μmol/L by the kinetic or enzymatic method, and 0.8 to 1.5 mg/dl, or 70 to 133 μmol/L by the older manual Jaffé reaction. The normal serum creatinine (sCr) varies with the subject's body muscle mass and with the technique used to measure it. In contrast, the rugged rancher who eats in excess of 125 g protein each day may have a normal BUN of 20 mg/dl. Her higher glomerular filtration rate (GFR), expanded extracellular fluid volume, and anabolism in the developing fetus contribute to her relatively low BUN of 5 to 7 mg/dl.
A BUN of 15 mg/dl would represent significantly impaired function for a woman in the thirtieth week of gestation. The range is wide because of normal variations due to protein intake, endogenous protein catabolism, state of hydration, hepatic urea synthesis, and renal urea excretion. The normal range of urea nitrogen in blood or serum is 5 to 20 mg/dl, or 1.8 to 7.1 mmol urea per liter. The BUN, then, is roughly one-half (7/15 or 0.466) of the blood urea. In Europe, the whole urea molecule is assayed, whereas in the United States only the nitrogen component of urea (the blood or serum urea nitrogen, i.e., BUN or SUN) is measured. Both are relatively small molecules (60 and 113 daltons, respectively) that distribute throughout total body water. Creatinine is the product of muscle creatine catabolism. Urea is the primary metabolite derived from dietary protein and tissue protein turnover. Urea and creatinine are nitrogenous end products of metabolism. The principle behind this ratio is the fact that both urea (BUN) and creatinine are freely filtered by the glomerulus however, urea reabsorbed by the tubules can be regulated (increased or decreased) whereas creatinine reabsorption remains the same (minimal reabsorption).
In the United States, both quantities are given in mg/dL The ratio may be used to determine the cause of acute kidney injury or dehydration. BUN only reflects the nitrogen content of urea (MW 28) and urea measurement reflects the whole of the molecule (MW 60), urea is just over twice BUN (60/28 = 2.14). In medicine, the urea-to-creatinine ratio ( UCR ), known in the United States as BUN-to-creatinine ratio, is the ratio of the blood levels of urea ( BUN) (mmol/L) and creatinine (Cr) (μmol/L). Medical laboratory value urea-to-creatinine ratio
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