In particular, prerenal disease should not be excluded by a normal ratio since diminished urea production due to decreased protein intake or underlying liver disease can prevent the expected rise in BUN due to increased tubular reabsorption.
Home Pharmacy Mnemonics Resources. BUN is disproportionately elevated relative to creatinine in serum. Dehydration or hypoperfusion is suspected. Can also be ATN. Some sources say the normal range is They are continually monitored by our internal peer-review process and if we see anyone making material science errors, we don't let them write for us again. Our goal is to not have a single piece of inaccurate information on this website. If you feel that any of our content is inaccurate, out-of-date, or otherwise questionable, please leave a comment or contact us at support selfhacked.
Note that each number in parentheses [1, 2, 3, etc. BUN blood urea nitrogen and creatinine are two blood tests that can reveal a lot about your metabolism, kidney, liver, and overall health.
BUN blood urea nitrogen and creatinine are two lab tests that are often ordered as part of a comprehensive metabolic panel.
Your doctor may order this panel to get an idea of your overall health and metabolism. BUN measures the amount of urea in your blood. Urea is a waste product made in the liver as the body processes protein. This protein is mostly derived from the diet, but it can also result from tissue protein turnover [ 1 , 2 , 3 ].
Urea is removed by the kidneys, but the rate of removal depends on the needs of the body. The kidneys can return different amounts of urea into the bloodstream depending on factors such as hydration and blood pressure. Since GFR is unaffected initially at least by this so-called prerenal azotemia, plasma creatinine remains within normal limits.
Specifically, it helps in distinguishing between an upper and lower gastrointestinal bleed. The anatomical site that is used to define the border between upper and lower gastrointestinal tract is the junction of the duodenum and jejunum, where the ligament of Treitz is attached.
The equivalent value for UCR is of course higher, [7],[9]. Quite apart from its role in localizing the site of a GI bleed, urea measurement has a role in determining the severity of bleeding.
In Pumphrey and Beck [14] demonstrated a positive correlation between estimated blood loss and plasma urea concentration among 57 patients with upper gastrointestinal hemorrhage. Confirmation that plasma urea concentration is a potential marker of substantial blood loss among patients with upper GI bleed led to inclusion of plasma urea concentration in the now well-validated Glasgow-Blatchford scoring system [15],[16],[17]. Chronic kidney disease CKD is defined by reduction in GFR, which in turn is associated with increased plasma creatinine and urea concentrations.
The causes of AKI are categorized under three headings: prerenal reduced renal perfusion, often because of hypovolemia , intrinsic renal damage to the kidney itself — glomerular or tubular , postrenal obstruction of urine flow [18]. Prerenal causes hypovolemia due to severe vomiting, blood loss, osmotic diuresis, etc.
Whatever the precise cause, prerenal AKI exists despite a presumed normally functioning kidney. Part of the response to the hemodynamic instability that underlies prerenal AKI is increased renal reabsorption of urea [19] and this contributes to the rising plasma urea consequent on reduced GFR.
These studies suggest that a high BCR can be associated with poor prognosis and therefore not necessarily indicative of just prerenal AKI. Credence for this view is provided by the observation that for critically ill patients with normal serum creatinine, plasma urea concentration is independently associated with mortality [23].
Heart and kidney function are closely related in health and disease. Pathologically this link is manifest as the cardiorenal syndrome [24]. These patients require immediate transfer to intensive care for optimal care and best chance of survival. A recent confirmatory study validated this clinical application of urea measurement [31].
The authors of this study retrieved plasma BUN urea results at admission and 24 hours later from patients with acute pancreatitis. Preand postdialysis plasma urea concentrations are used to calculate the urea reduction ratio URR thus:.
Urea measurement does, however, have some clinical value, especially when measured in tandem with plasma creatinine. Measurement of urea alone has proven value in assessment of patients with acute pancreatitis and monitoring effectiveness of hemodialysis. May contain information that is not supported by performance and intended use claims of Radiometer's products. See also Legal info. Radiometer and acutecaretesting. Printed from acutecaretesting. October Urea and creatinine concentration, the urea:creatinine ratio.
Summary This second of two articles on understanding the clinical value of measuring urea concentration explores the clinical value of simultaneous measurement of urea and creatinine and calculating the urea:creatinine ratio. For the blood concentration of an endogenously produced substance to most accurately reflect GFR in health and disease, that substance must have the following properties: It must be excreted only by the kidneys It must be freely filtered from blood at the glomerulus It must be neither reabsorbed from the filtrate to blood nor secreted from blood to the filtrate by renal tubulecells i.
For example: Patient A has: plasma urea 5. Freely filtered at glomerulus Yes Yes Not reabsorbed or secreted by renal tubule cells A variable quantity of urea reabsorbed from filtrate, dependent on state of hydration, renal blood flow, etc. Creatinine is not reabsorbed. Virtually all filtered creatinine appears in urine. However, a small amount is secreted by proximal tubules. Concentration in blood unaffected by factors other than GFR, i.
Plasma levels are ethnically and gender dependent, and are transiently increased by eating cooked meat. Gastrointestinal GI bleed Gastrointestinal bleeding represents a non-renal cause of increased plasma urea. Heart failure Heart and kidney function are closely related in health and disease. Clinical application of plasma urea measurement alone 1. Clinical application of plasma urea measurement alone 2. Higgins C. Urea and the clinical value measuring blood urea concentration.
Baum N et tal. Blood urea nitrogen and serum creatinine. Urology ; 5, 5: Traynor J et tal. How to measure renal function in clinical practice. BMJ Clinical research ed. McWilliam A et tal. Laboratory tests of renal function.
Lyman JL. Blood urea nitrogen and creatinine. Emerg Med Clin North Am ; 4, 2: Jurado R et tal. The decreased serum urea nitrogen-creatinine ratio. Arch Intern Med ; , Snook JA et tal.
Value of a simple biochemical ratio in distinguishing upper and lower sites of gastrointestinal haemorrhage. Lancet ; 1,
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