Abstract
Q1 How accurate is blood urea as a measure of renal function?
When we talk about “renal function” we usually mean the glomerular filtration rate (GFR). Each kidney has around 1,000,000 nephrons and the GFR is a measure of the function of all of these in both kidneys. Urea is a nitrogenous waste product, the level of which in the blood is usually <7 mmol/l. Blood urea rises in patients with kidney injury but is an imperfect marker of GFR for the following reasons: urea generation is low in patients with chronic liver disease and malnutrition and is disproportionately increased in those who are dehydrated (because urea is reabsorbed passively with sodium and water by the proximal tubule) or those who have gastrointestinal blood loss (because urea is absorbed from the gut).
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Further Reading
National Institute for Health and Care Excellence. Chronic kidney disease: early identification and management of chronic kidney disease in primary and secondary care. CG182. London: National Institute for Health and Care Excellence; 2014.
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Findlay, M., Isles, C. (2015). Assessment of GFR. In: Clinical Companion in Nephrology. Springer, Cham. https://doi.org/10.1007/978-3-319-14868-7_2
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DOI: https://doi.org/10.1007/978-3-319-14868-7_2
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