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A major measure of kidney function is the glomerular filtration rate (GFR). The glomerular filtration rate is the flow rate of filtered fluid through the kidney. The creatinine clearance rate (C Cr or CrCl) is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR.
The normal range of GFR, adjusted for body surface area, is 100–130 average 125 (mL/min)/(1.73 m 2) in men and 90–120 (mL/min)/(1.73 m 2) in women younger than the age of 40. In children, GFR measured by inulin clearance is 110 (mL/min)/(1.73 m 2 ) until 2 years of age in both sexes, and then it progressively decreases.
Urinary excretion rate = Filtration rate – Reabsorption rate + Secretion rate [1] Although the strictest sense of the word excretion with respect to the urinary system is urination itself, renal clearance is also conventionally called excretion (for example, in the set term fractional excretion of sodium ).
In the United States, acute failure affects about 3 per 1,000 people a year. [8] Chronic failure affects about 1 in 1,000 people with 3 per 10,000 people newly developing the condition each year. [1] [10] In Canada, the lifetime risk of kidney failure or end-stage renal disease (ESRD) was estimated to be 2.66% for men and 1.76% for women. [11]
A glomerular filtration rate (GFR) ≥ 60 mL/min/1.73 m 2 is considered normal without chronic kidney disease if there is no kidney damage present. Kidney damage is defined signs of damage seen in blood, urine, or imaging studies which includes lab albumin/creatinine ratio (ACR) ≥ 30. [ 59 ]
To clinically stage the degree of damage in this (and any) kidney disease, the serum creatinine is determined and used to calculate the estimated glomerular filtration rate . Normal eGFR is equal to or greater than 90ml/min/1.73 m 2. [34] On biopsy, the following classification has been suggested by Tervaert et al.: [35]
Risk: 1.5-fold increase in the serum creatinine, or glomerular filtration rate (GFR) decrease by 25 percent, or urine output <0.5 mL/kg per hour for six hours. Injury: Two-fold increase in the serum creatinine, or GFR decrease by 50 percent, or urine output <0.5 mL/kg per hour for 12 hours.
In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) over the renal plasma flow (RPF). Filtration Fraction, FF = GFR/RPF, or =. The filtration fraction, therefore, represents the proportion of the fluid reaching the kidneys that passes into the renal tubules. It is normally about 20%.