It is also sensitive to pH and temperature changes. This reaction is nonspecific and subject to interference from many noncreatinine chromogens, including acetone, acetoacetate, pyruvate, ascorbic acid, glucose, cephalosporins, barbiturates, and protein. The 1886 Jaffé reaction, in which creatinine is treated with an alkaline picrate solution to yield a red complex, is still the basis of most commonly used methods for measuring creatinine. Also chloral hydrate and guanethidine have been observed to increase BUN values. The specimen should not be collected in tubes containing sodium fluoride because the fluoride inhibits urease. The Astra system measures the rate of increase in conductivity of the solution in which urea is hydrolyzed.Įven though the test is now performed mostly on serum, the term BUN is still retained by convention. One system checks the decrease in absorbance at 340 mm when the ammonia reacts with alpha-ketoglutaric acid. These products, which are proportional to the concentration of urea in the sample, are assayed in a variety of systems, some of which are automated. In the more specific enzymatic methods, the enzyme urease converts urea to ammonia and carbonic acid. It still has limited specificity, however, as illustrated by spurious elevations with sulfonylurea compounds, and by colorimetric interference from hemoglobin when whole blood is used. It has been modified for use in autoanalyzers and generally gives relatively accurate results. 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.
#Urea normal range 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 (28/60 or 0.446) 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.
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