![]() 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. hypovolemia due to blood loss, vomiting, etc.Urea and creatinine are nitrogenous end products of metabolism.Plasma urea is disproportionately higher than increased Plasma urea normal/Plasma creatinine reduced Heart failure (without renal involvement).Plasma urea increased/Plasma creatinine normal Its plasma concentration to most accurately reflect GFR TABLE I: Comparison of urea and creatinine as markers of glomerular filtration rate (GFR) Criteria of a substance for Spuriously raised plasma creatinine (due to substances that interfere with creatinine estimation) can cause decreased BCR/UCR. Both are typically associated with reduced plasma urea but normal plasma creatinine. It is a feature of very rare inherited disorders of the urea cycle, and advanced liver disease. Decreased BCR/UCR is less common and usually of less clinical significance. The principal causes of increased BCR/UCR are listed in Table II below under these three headings. An increase in plasma urea is disproportionately greater than increased creatinine.Normal plasma urea and decreased plasma creatinine.Increased plasma urea and normal plasma creatinine.Increased BCR/UCR can present, theoretically at least, in one of three ways: To convert creatinine μmol/L to creatinine mg/dL – divide by 88.4Īll numerical values for the urea: creatinine ratio in this article will be BCR, not UCR values unless specifically stated. To convert urea mmol/L to BUN mg/dL – divide by 0.357 To calculate BCR for this patient we must first convert urea mmol/L to BUN mg/dL and creatinine μmol/L to creatinine mg/dL. This allows calculation of the more commonly used and better-referenced BCR. ![]() The UCR reference range is much higher than that for BCR (of the order 40-100) because of the difference between urea and urea nitrogen, and is less clearly defined than that for BCR, possibly because the ratio is less often used.Ī solution to this interpretative problem is to convert SI results for urea and creatinine to non-SI results before calculating the ratio. The factor of 1000 is needed to convert the creatinine result from μmol/L to mmol/L, the urea unit of measurement. The SI ratio (UCR) is plasma urea (mmol/L) / (plasma creatinine (μmol/L) divided by 1000). The reference range is around 8-15 and the most commonly used cut-off value to define increased BCR is 20. The non-SI ratio (BCR) is BUN (mg/dL) / plasma creatinine (mg/dL). These two different ways of reporting urea results give rise to two quite different values for the ratio. In all other parts of the world, urea results are expressed as the whole urea molecule (MW 60) and reported as urea in SI units (mmol/L). In the US and a few other countries, urea concentration is expressed as the nitrogen content of urea (MW 28) and reported as blood urea nitrogen (BUN) in non-SI units (mg/dL). The distinction between BUN: creatinine ratio (BCR) and urea: creatinine ratio (UCR) In most cases of chronic renal disease, the ratio remains relatively normal. When there is decreased formation of urea, as seen in liver disease, there is a decrease in the BUN/Creatinine ratio. Increased urea formation also results in an increase in the ratio, e.g. congestive heart failure or recent onset of urinary tract obstruction, will result in an increase in the BUN/Creatinine ratio. The BUN/Creatinine ratio is useful in the differential diagnosis of acute or chronic renal disease. The ratio may be used to determine the cause of acute kidney injury or dehydration. The units of creatinine are also different (μmol/L), and this value is termed the urea-to-creatinine ratio. In Canada and Europe, the units are also different (mmol/L).
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