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Encyclopedia > Glomerular filtration rate

Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time.[1] Clinically, this is often measured to determine renal function. Compare to filtration fraction. The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ... The glomerulus is a capillary bed found surrounded by the Bowmans capsule of the nephron in the vertebrate kidney. ... The Bowmans capsule(other names: capsula glomeruli, glomerular capsule) is a cup like sac at the beginning of the tubular component of a nephron in the mammalian kidney. ... In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology. ... In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF). ...

There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR).

Measurement using inulin

The GFR can be determined by injecting inulin (not insulin) into the plasma. Since inulin is neither reabsorbed nor secreted by the kidney after glomerular filtration, its rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter. (Dr. Amir Khan) Note: This article title may be easily confused with insulin. ...

Estimation using creatinine clearance

In clinical practice however, creatinine clearance is used to measure GFR. Creatinine is an endogenous molecule, synthesized in the body, which is freely filtered by the glomerulus (but also secreted by the renal tubules in very small amounts). Creatinine clearance is therefore a close approximation of the GFR. However, the approximation of the GFR calculation is best measured by the evaluation and visualization of the frequency and duration of urination. The GFR is typically recorded in units of volume per time, e.g. milliliters per minute (ml/min). Creatinine clearance is a method that estimates the glomerular filtration rate (GFR) of the kidneys. ...

Example: A person has a plasma creatinine concentration of 0.01 mg/ml and in 1 hour he excretes 75 mg of creatinine in the urine. The GFR is calculated as M/P (where M is the mass of creatinine excreted per unit time and P is the plasma concentration of creatinine).

$mbox{GFR }= frac{frac{75mbox{ mg}}{60mbox{ mins}}}{0.01mbox{ mg}/mbox{ml}} = 125 mbox{ ml}/mbox{min}$

Estimation using Cockcroft-Gault formula

The Cockcroft-Gault formula may be used to calculate an Estimated Creatinine Clearance, which in turn estimates GFR:[2]

$mbox{Creatinine clearance} = frac { mbox{(140 - Age)} times mbox{Mass (in kilograms)}} {mbox{72} times mbox{Plasma Creatinine (in mg/dl)}} times mbox{0.85 if female}$

MDRD formula

The MDRD formula estimates GFR using serum creatinine and age. Multipliers are used to adjust the estimation for race and gender.[3]

$mbox{eGFR} = mbox{186} times mbox{Serum Creatinine}^{-1.154} times mbox{Age}^{-0.203} times mbox{1.21 if Black} times mbox{0.742 if Female}$

Calculation using Starling equation

It is also theoretically possible to calculate GFR using the Starling equation.[4] Formulated in 1896 by the British physiologist Ernest Starling, the Starling equation illustrates the role of hydrostatic and oncotic forces (the so-called Starling forces) in the movement of fluid across capillary membranes. ...

Jv = Kf([PcPi] − σ[πc − πi])

The equation is used both in a general sense for all capillary flow, and in a specific sense for the glomerulus:

 General usage Glomerular usage Meaning of variable Relationship to GFR Description Pc Pgc Capillary hydrostatic pressure Direct Increased by dilation of afferent arteriole or constriction of efferent arteriole Pi Pbs Interstitial hydrostatic pressure Inverse πc πgc Capillary oncotic pressure Inverse Decreased by nephrotic syndrome πi πbs Interstitial oncotic pressure Direct Kf Kf Filtration coefficient Direct Increased by inflammation σ σ Reflection coefficient Inverse Jv GFR net filtration n/a

Note that ([PcPi] − σ[πc − πi]) is the net driving force, and therefore the net filtration is proportional to the net driving force. Hydrostatic pressure is the pressure exerted by a fluid due to its weight. ... The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. ... The Efferent arterioles are a group of blood vessels that are part of the urinary system of many animals. ... In blood plasma, the dissolved compounds have an osmotic pressure. ... An abscess on the skin, showing the redness and swelling characteristic of inflammation. ...

In practice, it is not possible to identify the needed values for this equation, but the equation is still useful for understanding the factors which affect GFR, and providing a theoretical underpinning for the above calculations.

Normal ranges

The normal ranges of GFR, adjusted for body surface area, are:[5]

• Males: 70 ± 14 mL/min/m2
• Females: 60 ± 10 mL/min/m2

GFR can increase due to hypoproteinemia because of the reduction in plasma oncotic pressure. GFR can also increase due to constriction of the efferent arteriole but decreases due to constriction of the afferent arteriole. Hypoproteinemia (or Hypoproteinaemia) is a condition where there is an abnormally low level of protein in the blood. ... The Efferent arterioles are a group of blood vessels that are part of the urinary system of many animals. ... The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. ...

Renal failure is the condition in which the kidneys fail to function properly. ... In medicine, dialysis is a type of renal replacement therapy which is used to provide an artificial replacement for lost kidney function due to renal failure. ... In the physiology of the kidney, tubuloglomerular feedback (TGF) is one of several mechanisms the kidney uses to regulate glomerular filtration rate (GFR). ... In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF). ...

References

1. ^ Physiology at MCG 7/7ch04/7ch04p11 - "Glomerular Filtration Rate"
2. ^ GFR Calculator at cato.at - Cockcroft-Gault - GFR calculation (Cockcroft-Gault formula)
3. ^ National Kidney Foundation (2002). Evaluation of Laboratory Measures for Clinical Assessment of Kidney Disease -- Guideline 4. Estimation of GFR. K/DOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification. Retrieved on 2007-07-16.
4. ^ Physiology at MCG 7/7ch04/7ch04p12 - "Forces Driving the Glomerular Filtration Rate":
5. ^ Creatinine clearance at merck.com - The normal ranges of GFR.

In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 197th day of the year (198th in leap years) in the Gregorian calendar. ... In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ...

Results from FactBites:

 RENAL BLOOD FLOW-GLOMERULAR FILTRATION RATE (4603 words) Since the glomerular capillary pressure (Pgc) i.e., filtration pressure is one important determinant of the amount of fluid that filters across the glomerular membrane into the proximal tubules, the phenomenon of renal autoregulation also serves to regulate the glomerular filtration rate by supporting the Pgc. The principle function of the JGA is adapting the GFR to early distal tubule fluid characteristics by modulating renin synthesis and release: this is known as the tubuloglomerular feedback (TGF) loop. The glomerular filtrate is defined as an ultrafiltrate of plasma, that is, a protein-free filtrate of plasma.
 Glomerular filtration rate - Wikipedia, the free encyclopedia (464 words) Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal glomerular capillaries into the Bowman's capsule per unit time. Since inulin is not reabsorbed by the kidney after glomerular filtration, its rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter. The GFR is calculated as M/P (where M is the mass of creatinine excreted per unit time and P is the plasma concentration of creatinine).
More results at FactBites »

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