Renal function

From Wikipedia, the free encyclopedia

(Redirected from Test of renal function)
Jump to: navigation, search

Renal function, in nephrology, is an indication of the state of the kidney and its role in renal physiology.

Contents

Most doctors use the plasma concentrations of creatinine, urea, and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease.

Unfortunately, BUN and creatinine will not be outside the normal range until 60% of total kidney function is lost. Hence, creatinine clearance is a more accurate measure and is used whenever renal disease is suspected or careful dosing of nephrotoxic drugs is required.

Another prognostic marker for kidney disease is Microalbuminuria — the measurement of small amounts of albumin in the urine that cannot be detected by urine dipstick methods.

In renal patients, the glomerular filtration rate (GFR) is used. This is calculated by comparing urine creatinine levels with the blood test results. It gives a more precise indication of the state of the kidneys. The GFR is expressed in ml/min. For most patients, a GFR over 60 ml/min is adequate. But, if the GFR has significantly declined from a previous test result, this can be an early indicator of kidney disease requiring medical intervention. The sooner kidney dysfunction is diagnosed and treated, the greater odds of preserving remaining nephrons, and preventing the need for dialysis.

Very often, the GFR is expressed as ml/min/1.73 m2. This is an indication that the GFR needs to be corrected for the body surface area (BSA). While most adults have a BSA that approaches 1.7 (1.6-1.9), extremely obese or slim patients should have their GFR corrected for their actual BSA.

{GFR corrected} = \frac{{GFR} \times {1.73}} {BSA}

BSA can be calculated on the basis of weight and height.

A commonly used surrogate marker for actual creatinine clearance is the Cockcroft-Gault formula, which employs creatinine measurements and a patient's weight to predict the clearance. The formula, as originally published, is:

{x} = \frac{(140-{age}) \times {ideal body weight} \times {0.85 (if female)}} {{72} \times {creatinine}}

This formula expects weight (actually mass) to be measured in kilograms and creatinine to be measured in mg/dL, as is standard in the USA. The resulting value is multiplied by a constant of 0.85 if the patient is female. This formula is useful because the calculations are relatively simple and can often be performed without the aid of a calculator.

A modification of this formula, useful for the common units of measure, is:

{x} = \frac{(140-{age}) \times {weight} \times {constant} } {creatinine}

This formula uses metric units (weight in kilograms, creatinine in µmol/L). The constant is 1.23 for men and 1.04 for women.

It is named after the scientists who first published the formula (Cockcroft & Gault, 1976). The equation is popular because it is easy to calculate.

The most recently advocated formula for calculating the GFR is the one that was developed as a result of the Modification of Diet in Renal Disease (MDRD) study (Levey et al 1999).

For creatinine in mg/dL

{x} = 186 \times {creatinine}^{-1.154} \times {age}^{-0.203} \times {constant}

For creatinine in µmol/L

{x} = 32788 \times {creatinine}^{-1.154} \times {age}^{-0.203} \times {constant}

The constant is 1 for a white male, and is multiplied with 0.742 for females and multiplied with 1.21 for African Americans.

Creatinine levels in µmol/L can be converted to mg/dL by dividing them by 88.4. The 32788 number above is equal to 186×88.41.154.

A more elaborate version of the MDRD equation also includes serum albumin and blood urea nitrogen levels:

{GFR} = 170 \times {[Pcr]}^{-0.999} \times {[Age]}^{-0.176} \times {[0.762\ if\ patient\ is\ female]} \times {[1.180\ if\ patient\ is\ black]} \times {[SUN]}^{-0.170} \times {[Alb]}^{+0.318}
{[Pcr]} = serum\ creatinine\ concentration\ (mg/dL)
{[SUN]} = serum\ urea\ nitrogen\ concentration\ (mg/dL)
{[Alb]} = serum\ albumin\ concentration\ (g/dL)

In children, the Schwartz formula is used. This employs the serum creatinine, the child's height and a constant to estimate the creatinine clearance.

{x} = \frac{ {k} \times {height} }{creatinine}

k - for height in some units and creatine in some other units, the constant is 0.33-0.45 in infants, 0.55 in children or adolescent girls, or 0.70 in adolescent boys.

v • d • e
Urinary system, physiology: renal physiology and acid base physiology
Filtration Ultrafiltration - Countercurrent exchange
Hormones affecting filtration Antidiuretic hormone (ADH) - Aldosterone - Atrial natriuretic peptide
Secretion/clearance Pharmacokinetics - Clearance of medications
Reabsorption Na+
Endocrine Renin - Erythropoietin (EPO) - Calcitriol (Active vitamin D) - Prostaglandins
Assessing Renal function / Measures of dialysis Glomerular filtration rate - Creatinine clearance - Renal clearance ratio - Urea reduction ratio - Kt/V - Standardized Kt/V - Hemodialysis product
Acid base physiology Fluid balance - Darrow Yannet diagram - Body water - Interstitial fluid - Extracellular fluid - Intracellular fluid/Cytosol - Plasma - Transcellular fluid - Base excess - Davenport diagram - Anion gap - Arterial blood gas
Buffering/compensation Bicarbonate buffering system - Respiratory compensation - Renal compensation
Retrieved from "http://en.wikipedia.org/wiki/Renal_function"
Advanced Search
Included Web Search Engines


Safe Search

close

Top Matching Results

Occasionally Search.com will highlight specialized results that are based on the context of your query. Examples of specialized results include specific links to news, images, or video.

Top Matching Results may highlight information from other Search.com pages, content from the CNET Network of sites, or third party content. The listings are based purely on relevance. Search.com does not receive payment for listings in this section but our partners that provide this data may get paid for listing these products.

Sponsored Links

This section contains paid listings which have been purchased by companies that want to have their sites appear for specific search terms and related content. These listings are administered, sorted and maintained by a third party and are not endorsed by Search.com.

Search Results

Search.com sends your search query to several search engines at one time and integrates the results into one list which has been sorted by relevance using Search.com's proprietary algorithm. You can customize the list of search engines included in your metasearch from the preferences.

The search engines that are used in your metasearch may allow companies to pay to have their Web sites included within the results. To view the Paid Inclusion policy for a specific search engine, please visit their Web site. Search.com does not accept payment or share revenue with any search engine partner for listings in this section.