The measurement of urea in the blood is done via Blood urea nitrogen test or simply referred to as BUN.Ĭreatinine, on the other hand, is a molecular protein produced by the muscle and is relatively freely filtered by the kidneys. As the peptide bond breakage creates nitrogenous waste products, ammonia is produced which is converted into a nontoxic waste called urea by the liver. These are then absorbed through the gut and are the building blocks for protein. Normally, when we eat protein, the peptide bond gets broken to yield amino acids. One of such biomarker sets is that of the BUN: Creatinine ratio. However, when you consider this objectively to define how much a person is dehydrated, some laboratory biomarkers can help. For the most part, dehydration is a clinical diagnosis, from signs and symptoms that signify loss of water and electrolytes from the body. One of the many incomplete tasks in the hydration space is using biomarkers to objectively identify dehydration. hypovolemia due to blood loss, vomiting, etc.The BUN : Creatinine ratio: Understanding Biomarkers of Hydration and Kidney Function.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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