Men have more muscle mass than women and hence, tend to have higher levels of creatinine than women. It is usually produced at a constant rate by the body, however, it can vary according to the muscle mass. Creatinine is a break-down product of creatine phosphate in muscle. This is the ratio of blood urea nitrogen to serum creatinine. The BUN is roughly one-half (28/60 or 0.446) of the blood urea. In Europe, the whole urea molecule is taken into consideration while in the United States, only the nitrogen component of urea (the blood urea nitrogen or serum urea nitrogen, i.e., BUN or SUN) is measured. Muscle creatine catabolism generates creatinine. Urea is generated from dietary protein and tissue protein turnover. hypovolemia due to blood loss, vomiting, etc.Urea and creatinine are nitrogenous end products of body 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).

Normal ranges BUN