Renal clearance

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Renal clearance


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Renal clearance

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A researcher is studying the renal clearance of Drug A from a patient. Drug A has a urine concentration of U and plasma concentration of P. The urine flow rate is F. Which of the following best describes the rate at which Drug A is renally cleared from this patient?  

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Clearance (CL) of drugs p. 231

Drug clearance p. 732


clearance p. 608

Glucose clearance p. 608


glucose clearance p. 608

Proximal convoluted tubules (PCT)

glucose clearance and p. 608

Renal clearance p. 606, 733

Splay (glucose clearance) p. 608


bacterial clearance by p. 125

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In order for the body to function properly, it needs a way to get rid of toxins and other waste materials. That’s where the kidneys come in. Their main function is to filter the blood and remove any unwanted substances from the body. Now, the first step in blood filtration happens at the glomerulus - a tiny bed of capillaries surrounded by the Bowman’s capsule. The glomerular filtration barrier is made up of three layers and together they separate the blood inside the glomerular capillaries from the fluid inside Bowman’s capsule. They work like a sieve, allowing water and some solutes in the plasma like sodium, to pass into Bowman’s space, while keeping negatively charged particles like proteins, or large particles like red blood cells in the blood. The filtered fluid, now called pre-urine, leaves the Bowman’s space and travels through the nephron.

The nephron is the basic unit of the kidney, and is essentially one long tube bent into a “U” shape. Different sections of this tube either reabsorb substances back into systemic circulation or actively secrete them into the nephron to be excreted in urine.

Renal clearance of a substance refers to how quickly a particular substance is removed from the plasma by the kidney and excreted in urine. So something with a high renal clearance means that it will be quickly removed from the blood, and vice versa. There’s a formula to calculate renal clearance for some substance X.

In this formula, C stands for the renal clearance which is the volume of blood plasma that’s cleared of that substance over time in minutes. C equals the concentration of the substance in urine [U]x multiplied by the urine flow rate (V) which is the amount of urine excreted over time in minutes. All of that’s divided by the plasma concentration of the substance [P]x. So, if the urine concentration is high but the plasma concentration is low, then that must mean that a lot of the substance was removed from the blood, leading to a high renal clearance. As a general rule, small, uncharged substances like inulin, which is a small inert polysaccharide molecule, have a relatively easy time passing through the glomerulus.


Renal clearance is the rate at which certain substances are removed from the plasma by the kidneys. It helps to measure how well the kidneys are filtering waste products from the blood. A higher renal clearance suggests the substance may be cleared almost completely in one pass through the kidneys, whereas a low value suggests that a substance may not be eliminated by the kidneys at all. In calculations, the renal clearance (C) of a substance x �, will be directly proportional to the urine concentration of the substance x ([U]x) and the urine flow rate (V), and inversely proportional to x's plasma concentration ([P]x): C=[U]x V[P]x


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "The development of the clearance concept" J Nephrol (2004)
  6. "Whither goest Kt/V?" Kidney International (2000)
  7. "The genesis of the square meter-hour hypothesis" Trans Am Soc Artif Intern Organs (1971)

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