In the medical world, the BUN-to-creatinine ratio is the ratio of two serum laboratory values, blood urea nitrogen (BUN) (mg/dL) and serum creatinine (Cr) (mg/dL). Outside the United States, particularly in Canada and Europe, the term urea is cut off used (though still chemically the same blood) and different units (mmol/L). The creatinine unit is also different (? Mol/L), and this value is called the ratio of urea-creatinine . Ratios can be used to determine the cause of acute or dehydrated kidney injury.
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) while creatinine reabsorption remains the same (minimal reabsorption).
Video BUN-to-creatinine ratio
Definisi
Urea and creatinine are the nitrogen end products of metabolism. Urea is a major metabolite derived from dietary protein and protein tissue turnover. Creatinine is the product of muscle creatin catabolism. Both are relatively small molecules (60 and 113 dalton, respectively) that are distributed throughout the total body water. In Europe, all urea molecules are tested, whereas in the United States only urea nitrogen components (serum blood or nitrogen urea, ie BUN or SUN) are measured. The BUN, then, is about one half (7/15 or 0.466) of blood urea.
The normal range of urea nitrogen in the blood or serum is 5 to 20 mg/dl, or 1.8 to 7.1 mmol urea per liter. Wide range due to normal variations due to protein intake, endogenous protein catabolism, hydration state, hepatic urea synthesis, and renal urea excretion. A 15 mg/dl BUN will represent a significant disturbance function for a woman in the third week of pregnancy. Higher glomerular filtration rates (GFR), expanded extracellular fluid volume, and anabolism in developing fetuses contribute to a relatively low BUN of 5 to 7 mg/dl. Conversely, a rough breeder who eats more than 125 g of protein daily may have a normal BUN of 20 mg/dl.
Normal serum creatinine (sCr) varies with the body muscle mass of the subject and by the technique used to measure it. For adult men, the normal range is 0.6-1.2 mg/dl, or 53 to 106? Mol/L with kinetic or enzymatic method, and 0.8 to 1.5 mg/dl, or 70 to 133? Mol/L by Jaffa reaction  © older manual. For adult women, with muscle mass generally lower, the normal range is 0.5-1.1 mg/dl, or 44 to 97? Mol/L with enzymatic method.
Maps BUN-to-creatinine ratio
Technique
Various methods for BUN analysis and creatinine have evolved over the years. Most of the current usage is automated and provides clinically reliable and reproducible results.
There are two general methods for the measurement of urea nitrogen. Diacetyl reaction, or Fearon, develops yellow chromogen with urea, and this is quantified by photometry. These have been modified for use in autoanalyzers and generally provide relatively accurate results. It still has limited specificity, however, as illustrated by a false increase with sulfonylurea compounds, and by colorimetric disorders of hemoglobin when intact blood is used.
In more specific enzymatic methods, urease enzymes convert urea into ammonia and carbonic acid. These products, which are proportional to the urea concentrations in the sample, are tested in various systems, some of which are automatic. One system checks the absorbance decrease at 340 mm when the ammonia reacts with alpha-ketoglutaric acid. The Astra system measures the rate of increase in the conductivity of the solution in which urea is hydrolyzed.
Although tests are now performed mostly on serum, the term BUN is still maintained by convention. Specimens should not be collected in tubes containing sodium fluoride because fluoride inhibits urease. Also chloral hydrate and guanetidine have been observed to increase the BUN value.
Reaction 1886 JaffÃÆ'Â ©, where creatinine is treated with an alkaline picate solution to produce a red complex, is still the basis of the most frequently used method for measuring creatinine. This reaction is neither specific nor disturbed by many noncreatinin chromogens, including acetone, asetoacetate, pyruvate, ascorbic acid, glucose, cephalosporins, barbiturates, and proteins. It is also sensitive to changes in pH and temperature. One or more mods designed to undo this error source are used in most of the current clinical laboratories. For example, the recent modification of kinetic rate, which isolates short time intervals in which only true creatinine contributes to total color formation, is the basis of Astra's modular system.
More specifically, non-JaffÃÆ' Â © tests have also been developed. One of them is the automatic dry-slide enzymatic method, measuring the ammonia produced when creatinine is hydrolyzed by iminohydrolase creatinine. Its simplicity, precision, and speed greatly recommend it for routine use in clinical laboratories. Only 5-fluorocytosine interferes significantly with the test.
Creatinine should be determined in plasma or serum rather than intact blood because erythrocytes contain large amounts of noncreatinin chromatin. To minimize creatinine conversion to creatinine, the specimen should be as fresh as possible and kept at pH 7 during storage.
The amount of urea produced varies with the delivery of the substrate to the liver and the adequacy of liver function. This is enhanced by a high protein diet, with gastrointestinal bleeding (based on plasma protein levels of 7.5 g/dl and hemoglobin 15 g/dl, 500 ml of whole blood equivalent to 100 g protein), by catabolic processes such as fever or infection, and by antianabolic drugs such as tetracycline (except doxycycline) or glucocorticoids. This is decreased by low-protein diets, malnutrition or starvation, and by impaired metabolic activity in the liver due to parenchymal liver disease or, rarely, for congenital deficiency of urea cycle enzymes. Normal subjects on the 70 g protein diet produce about 12 g urea daily.
This newly synthesized urea distributes the total body water total. Some of it is recycled through the enterohepatic circulation. Typically, small amounts (less than 0.5 g/day) are lost through the digestive tract, lungs, and skin; during exercise, a substantial fraction can be excreted in perspiration. Most urea, about 10 g daily, is excreted by the kidney in a process that begins with glomerular filtration. At high urine flow rate (more than 2 ml/min), 40% of the filtered load is reabsorbed, and at a flow rate lower than 2 ml/min, reabsorption can increase up to 60%. Low flow, as in urinary tract obstruction, allows more time for reabsorption and is often associated with increased antidiuretic hormone (ADH), which increases the permeability of the terminal collecting tubule to urea. During ADH-induced antidiuresis, urea secretion contributes to intratubular ureal concentrations. The subsequent accumulation of urea in the inner medulla is essential for the process of urine concentration. Reabsorption also increases due to volume contraction, decreased renal plasma flow as in congestive heart failure, and decreased glomerular filtration.
Creatinine formation begins with transamidination from arginine to glycine to form glycocyamine or guanidoacetic acid (GAA). This reaction occurs mainly in the kidneys, but also in the small intestine and pancreatic mucosa. GAA is transported to the liver where it is methylated by S-adenosyl methionine (SAM) to form creatine. Creatine enters the circulation, and 90% of it is taken up and stored by muscle tissue.
Interpretation
Serum value is normal
Rasio Serum
Increased BUN: Cr due to low or low-normal creatinine and BUN in the reference range may not be clinically significant.
Causes of specific height
Acute kidney injury (previously called acute renal failure)
The ratio is a prediction of prerenal injury when BUN: Cr exceeds 20 or when urea: Cr exceeds 100. In prerenal injury, urea increases disproportionately to creatinine due to an increase in proximal tubular reabsorption following the increase in sodium and water transport.
Gastrointestinal bleeding
This ratio is useful for the diagnosis of bleeding from the gastrointestinal tract (GI) in patients who do not come with clear vomiting blood. In children, the BUN ratio: Cr 30 or greater has a sensitivity of 68.8% and a specificity of 98% for upper gastrointestinal bleeding.
The general assumption is the increased ratio due to the digestive amino acids, because the blood (excluding water) is largely composed of hemoglobin protein and is broken down by the upper GI tract digestive enzymes into amino acids, which are then reabsorbed in GI. tractate and broken down into urea. However, an increase in BUN: Cr ratio was not observed when other high protein loads (eg, steak) were consumed. Secondary renal hypoperfusion in the blood loss from GI bleeding has been postulated to explain the increased BUN: Cr ratio. However, other studies have found that renal hypoperfusion can not fully explain elevation.
Seniors
Due to decreased muscle mass, elderly patients may have a high BUN: Cr at baseline.
Other causes
Hypercatabolic state, high doses of glucocorticoids, and large hematoma resorption have all been mentioned as the cause of a disproportionate increase in BUN compared with creatinine.
References
External links
- Agrawal M, Swartz R (April 2000). "Acute renal failure". Doctor Am Fam . 61 (7): 2077-88. PMID 10779250.
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