Renal function

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Kidney function , in nephrology, is an indication of renal condition and its role in renal physiology. Glomerular filtration rate ( GFR ) illustrates the rate of fluid flow filtered through the kidneys. The creatinine clearance rate ( C _Cr or CrCl ) is the clean volume of blood plasma from creatinine per unit of time and is a a useful measure for estimating GFR. The creatinine clearance exceeds GFR because of creatinine secretion, which can be blocked by cimetidine. In alternative fashion, too high by longer serum creatinine methods leads to underestimation of creatinine clearance, which gives a less biased GFR estimate. Both GFR and C _Cr can be calculated accurately with comparative measurements of substances in the blood and urine, or estimated by the formula using only blood test results ( eGFR and eC _Cr ).

The results of this test are used to assess the function of renal excretion. The stage of chronic kidney disease is based on the category of GFR as well as albuminuria and the cause of kidney disease.

Doses of drugs excreted primarily through urine may need to be modified based on either GFR or creatinine clearance.

Video Renal function

Indirect tags

Most physicians use the plasma concentration of creatinine and urea (U) waste wastes, as well as electrolytes (E), to determine renal function. These steps are sufficient to determine whether a patient has kidney disease.

However, blood urea nitrogen (BUN) and creatinine will not be raised above the normal range up to 60% of the total kidney function disappears. Therefore, a more accurate Glomerular filtration rate or an approximation of creatinine clearance is measured whenever renal disease is suspected or a careful dose of nephrotoxic drugs is required.

Increased levels of protein in the urine indicate some kidney disease. The most sensitive marker of proteinuria is an increase in urine albumin. The continuous presence of more than 30 mg of albumin per gram of creatinine in urine is diagnostic of chronic kidney disease (microalbuminuria is a level of 30 mg/L to 299 mg/liter of urine or 30-299 mg/24 hours, the concentration of albumin in urine undetected by ordinary urine dipstick method).

Maps Renal function

Glomerular filtration rate

Glomerular filtration rate ( GFR ) is the volume of fluid filtered from the renal glomerular capillaries (kidney) into the Bowman capsule per unit of time. The GFR physiological treatment center is a differential basal tone of afferent and efferent arterioles (see diagram). In other words, the degree of filtration depends on the difference between high blood pressure created by input vasoconstriction or afferent arterioles versus low blood pressure created by a lower vasoconstriction of output or efferent arterioles.

GFR is equal to the Cleansing Level when each solute can be freely filtered and not absorbed or secreted by the kidneys. The level measured is the amount of substance in the urine that comes from the blood volume that can be calculated. Related to this principle with the equation below - for the substance used, the product of urine concentration and urine flow is equal to the mass of the substance released during the time the urine has been collected. This mass is equal to the mass filtered in the glomerulus because nothing is added or discarded in the nephron. Dividing this mass by the plasma concentration gives the plasma volume originally from the mass, and thus the volume of the plasma fluid that has entered the Bowman capsule within that time period. GFR is usually recorded in units volume per time , for example, milliliters per minute (mL/mnt). Compare with the filtration fraction.

${\ displaystyle GFR = {\ frac {{\ mbox {Urine Concentration}} \ times {\ mbox {Urine Flow}}} {\ mbox {Plasma Concentration }}}}$

There are several different techniques used to calculate or estimate glomerular filtration rate (GFR or eGFR). The above formula only applies to GFR calculations when equal to Cleaning Level.

Measurement using inulin

GFR can be determined by injecting inulin or an inulin-analogue sinistrin into the plasma. Since both inulin and sinistrin are not absorbed or absorbed by the kidneys after glomerular filtration, their excretion rate is directly proportional to the water filtration rate and the solute across the glomerular filter. Compared with the MDRD formula, inulin permits slightly overestimated glomerular function. In early stage kidney disease, inulin clearance may remain normal due to hyperfiltration in the remaining nephrons. Incomplete urine collection is an important source of errors in inulin clearance measurements.

Measurement with radioactive tracker

GFR can be measured accurately using radioactive substances, especially Chromium-51 and Technetium-99m. This approximates the ideal Inulin property (only undergoing glomerular filtration) but can be measured more practically with only a small amount of urine or blood sample. Measurement of kidney or plasma cleansers ⁵¹ Cr-EDTA is widely used in Europe but not available in the United States, where ^99m Tc-DTPA may be used instead. Cleansing of the kidneys and plasma ⁵¹ Cr-EDTA has proven to be accurate compared to the gold standard, Inulin. Use of ⁵¹ Cr-EDTA is considered a standard reference measure in the UK guide.

Definition of pressure

More precisely, GFR is the fluid flow rate between the glomerular capillaries and the Bowman capsule:

${\ displaystyle {\ operatorname {d} Q \ over \ operatorname {d} t} = K_ {f} \ kali (P_ {G} -P_ {B} - \ Pi _ {G} \ Pi _ {B})}  ÂÂ$

Dimana:

• ${\ displaystyle {\ operatorname {d} Q \ over \ operatorname {d} t}}  ÂÂ$ adalah GFR.
• ${\ displaystyle K_ {f}}  ÂÂ$ disebut filtrasi konstan dan didefinisikan sebagai produk dari konduktivitas hidrolik dan luas permukaan kapiler glomerulus.
• ${\ displaystyle P_ {G}}  ÂÂ$ adalah tekanan hidrostatik dalam kapiler glomerulus.
• ${\ displaystyle P_ {B}}  ÂÂ$ adalah tekanan hidrostatik di dalam kapsul Bowman.
• ${\ displaystyle \ Pi _ {G}}  ÂÂ$ adalah tekanan osmotik koloid dalam kapiler glomerulus.
• dan ${\ displaystyle \ Pi_ {B}}  ÂÂ$ adalah tekanan osmotik koloid dalam kapsul Bowman.

K _f

Since this constant is a measurement of hydraulic conductivity multiplied by the capillary surface area, it is almost impossible to measure physically. However, it can be determined experimentally. The GFR determination method is listed in the section above and below and it is clear from our equation that ${\ displaystyle K_ {f}}$ can be found by dividing experimental GFR with clean filtration pressure:

${\ displaystyle K_ {f} = {\ frac {\ textrm {GFR}} {\ textrm {Net \ Filt. \ Tekanan}}} = {\ frac {\ textrm {GFR}} {(P_ {G} -P_ {B} - \ Pi_ {G} \ Pi_ {B})}}}  ÂÂ$

P _G

The hydrostatic pressure in the glomerular capillaries is determined by the difference in pressure between the immediate fluid from the afferent arterioles and leaving through the efferent arterioles. The pressure difference is estimated by the product of the total resistance of the arteriole in question and the blood flow through it:

${\ displaystyle P_ {a} -P_ {G} = R_ {a} \ kali Q_ {a}}  ÂÂ$

${\ displaystyle P_ {G} -P_ {e} = R_ {e} \ kali Q_ {e}}  ÂÂ$

Dimana:

• ${\ displaystyle P_ {a}}  ÂÂ$ adalah tekanan arteriol aferen.
• ${\ displaystyle P_ {G}}  ÂÂ$ adalah tekanan hidrostatik dalam kapiler glomerulus.
• ${\ displaystyle P_ {e}}  ÂÂ$ adalah tekanan arteriol eferen.
• ${\ displaystyle R_ {a}}  ÂÂ$ adalah resistansi arteri aferen.
• ${\ displaystyle R_ {e}}  ÂÂ$ adalah resistansi arteriol eferen.
• ${\ displaystyle Q_ {a}}  ÂÂ$ adalah fluks arteriol aferen.
• Dan, ${\ displaystyle Q_ {e}}  ÂÂ$ adalah fluks arteriol eferen.

P _B

The pressure on Bowman's capsule and proximal tubules can be determined by the difference between the pressure in Bowman's capsule and the descending tubule:

${\ displaystyle P_ {B} -P_ {d} = R_ {d} \ kali (Q_ {a} -Q_ {e})}  ÂÂ$

Dimana:

• ${\ displaystyle P_ {d}}  ÂÂ$ adalah tekanan pada tubulus yang turun.
• Dan, ${\ displaystyle R_ {d}}  ÂÂ$ adalah hambatan tubulus descending.

? _G

Plasma blood has many good proteins in it and they exert an inwardly directed force called colloidal osmotic pressure in water in a hypotonic solution across the membrane, that is, in the Bowman capsule. Because plasma proteins are barely capable of escaping from glomerular capillaries, these oncotic pressures are defined, simply, by ideal gas law:

${\ displaystyle \ Pi _ {G} = RTc}  ÂÂ$

Where:

• R is the universal gas constant
• T is the temperature.
• And, c is the concentration in the plasma mol/l protein (remember the solute can freely diffuse through the glomerular capsule).

? _B

This value is almost always thought to be equal to zero because, in a healthy nephron, there should be no protein in the Bowman Capsule.

src: www.onlinejacc.org

Creatinine-based approach from GFR

In clinical practice, however, creatinine clearance or an estimated creatinine clearance based on serum creatinine levels is used to measure GFR. Creatinine is produced naturally by the body (creatinine is the product of creatine phosphate splitting, found in muscle). It is freely filtered by the glomerulus, but is also actively secreted by peritubulus capillaries in very small amounts so that creatinine expenditure exceeds the actual GFR by 10% to 20%. The margin of error is acceptable, given the ease of creatinine cleansing measured. Unlike precise GFR measurements involving constant inulin infusion, creatinine is at a steady-state concentration in the blood, and thus measuring creatinine clearance is far less practical. However, GFR creatinine estimates have their limitations. All estimation equations depend on the predicted 24-hour creatinine excretion rate, which is a function of varying muscle mass. One equation, the Cockcroft and Gault equations (see below) are incorrect for the race. With higher muscle mass, serum creatinine will be higher for any given clearance level.

A common mistake made when only looking at serum creatinine is failure to account for muscle mass. Therefore, older women with a serum creatinine of 1.4 mg/dL may actually have a fairly severe renal insufficiency rate, whereas muscular young males may have normal levels of kidney function at serum creatinine levels. Creatinine-based equations should be used with caution in cachectic patients and patients with cirrhosis. They often have very low muscle mass and much lower creatinine excretion rates than the equation suggests, so cirrhotic patients with serum creatinine 0.9 mg/dL may have severe renal insufficiency rates.

Clean creatinine C _Cr

One method for determining GFR from creatinine is to collect urine (usually for 24 hours) to determine the amount of creatinine secreted from the blood over a certain time interval. If someone removes 1440 mg in 24 hours, this is equivalent to eliminating 1 mg/min. If the blood concentration is 0.01 mg/mL (1 mg/dL), it can be said that 100 mL/min of blood is being "clean" from creatinine, because, to get 1 mg of creatinine, 100 ml of blood contains 0.01 mg/mL needs to be cleaned.

Creatinine clearance (C _Cr ) was calculated from creatinine concentrations in collected urine samples (U _Cr ), urine flow rate (V dt ), and plasma concentration (P _Cr ). Since the results of urine concentration and urine flow rate result in a rate of creatinine excretion, which is the rate of removal from the blood, creatinine clearance is calculated as the removal rate per minute (U _Cr ÃÆ' â € "V dt ) divided by plasma creatinine concentration. This is usually represented as mathematically as

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$   ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, <Â> C                 Â                           =                                  Â               U                        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, C                 r        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,       Â            ÃÆ' -                                    ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...                    V                  ?     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                      Â      Â Â

                   ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, C         Â         ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,          Â                                {\ displaystyle C_ {Cr} = {\ frac {U_ {Cr} \ times {\ dot {V}}} {P_ {Cr}}}}  Â

Contoh: Seseorang memiliki konsentrasi kreatinin plasma 0,01 mg/ml dan dalam 1 jam menghasilkan 60 ml urin dengan konsentrasi kreatinin 1,25 mg/mL.

${\ displaystyle C_ {Cr} = {\ frac {1.25mg/mL \ times {\ frac {60mL} {60min}}} {0.01mg/mL}} = { \ frac {{1.25mg/mL} \ times {1mL/min}} {0.01mg/mL}} = {\ frac {1.25mg/min} {0.01mg/mL}} = {125mL/min}}  ÂÂ$

The general procedure involves the collection of urine 24 hours, from the bladder one morning to the bladder content the next day, with a comparative blood test then taken. Flow rate is still calculated per minute, then:

${\ displaystyle C_ {Cr} = {\ frac {U_ {Cr} \ \ times \ {\ mbox {24-hour volume}}} {P_ { Cr} \\ times \ 24 \ times 60min}}} Â Â$

To allow comparison of outcomes between people of different sizes, C _Cr is often corrected for body surface area (BSA) and expressed as compared to men of average size as mL/min/1.73 m ² . While most adults have BSA that is close to 1.7 m ² (1,6 m ² to 1.9 m ² ), the patient very fat or slim must have C _Cr corrected for their actual BSA .

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â}$ _{  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, <Â> C                 Â      ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÃ, -      ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂï <½Â      Â       Â       Â             e      ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂï <½Â     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂï <½Â            e      Â                           =                                                ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ...        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, C                        Â ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, C                    r     ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        Â        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                 Ã,            ÃÆ' -             Ã,                             1.73        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                                  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, <Â> B S              A                                            {\ displaystyle C_ {Cr-corrected} = {\ frac {{C_ {Cr}} \\ times \ {1.73}} {BSA}}}  Â}

BSA can be calculated by weight and height.

24-hour urine collection to assess creatinine clearance is no longer widespread, due to difficulties in ensuring complete collection of specimens. To assess the adequacy of a complete collection, one always counts the amount of creatinine excreted over a 24-hour period. This amount varies with muscle mass, and is higher in young people vs. older, blacks vs whites, and in men vs women. A low or high 24-hour creatinine excretion rate suddenly cancels the test. However, in cases where estimates of creatinine release from serum creatinine are unreliable, creatinine clearance remains a useful test. These cases include "estimates of GFR in individuals with variations in dietary intake (vegetarian diet, creatine supplement) or muscle mass (amputations, malnutrition, muscle wasting), because these factors are not specifically taken into account in predictive equations."

src: www.onlinejacc.org

Estimated value

A number of formulas have been designed to estimate GFR or C _cr values ​​based on serum creatinine levels. Where not stated serum creatinine expressed in mg/dL, not Ã,Âμmol/L - divided by 88.4 to convert from Ã,Âμmol/Lto mg/dL.

Estimated creatinine clearance rate (eC _Cr ) using the Cockcroft-Gault formula

A commonly used substitute marker for estimating creatinine clearance is the Cockcroft-Gault (CG) formula, which in turn estimates GFR in ml/min: Named according to scientists, asthmologist Donald William Cockcroft (born 1946) and nephrologist Matthew Henry Gault (1925 -2003), who first published the formula in 1976, and used serum creatinine and patient weight measurements to predict creatinine clearance. The formula, as originally published, is:

$Â\; Â{\displaystyle Â\; Â\; Â\; Â\; Â\; Â\; Â\; ÂeÂ\; Â\; Â\; Â\; Â\; Â\; Â}$   ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ, <Â> C                 Â                           =                                                                           (140 - Age)    ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                 Ã,            ÃÆ' -             Ã,                              <<<<<<<<<<<<<<<<<<<<<< Mass (in kilograms)    ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,        ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ,                 Ã,            ÃÆ' -             Ã,             [                             0.85               Ã,      Â         me               f               Ã,         ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ

Source of the article : Wikipedia