Renal function

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Renal function

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Overview

In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology.

Indirect markers

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.

Glomerular filtration rate

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.

Cockcroft-Gault formula

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.

MDRD formula

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)

Children: Schwartz

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.

References

See also

External links

v • d • e
Urinary system, physiology: renal physiology and acid base physiology
FiltrationRenal blood flow - Ultrafiltration - Countercurrent exchange
Hormones affecting filtrationAntidiuretic hormone (ADH) - Aldosterone - Atrial natriuretic peptide
Secretion/clearancePharmacokinetics - Clearance of medications
ReabsorptionSolvent drag -Na+ - Cl- -urea -glucose -oligopeptides -protein
EndocrineRenin - Erythropoietin (EPO) - Calcitriol (Active vitamin D) - Prostaglandins
Assessing Renal function / Measures of dialysisGlomerular filtration rate - Creatinine clearance - Renal clearance ratio - Urea reduction ratio - Kt/V - Standardized Kt/V - Hemodialysis product - PAH clearance (Effective renal plasma flow - Extraction ratio)
Acid base physiologyFluid 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/compensationBicarbonate buffering system - Respiratory compensation - Renal compensation
v • d • e
WikiDoc Research Resources for Renal function
Articles on Renal functionMost recent articles on Renal function • Most cited articles on Renal function • Review articles on Renal function • Articles on Renal function in N Eng J Med, Lancet, BMJ
Media (Slides, Video, Images, MP3) on Renal functionPowerpoint slides on Renal function • Images of Renal function • Photos of Renal function • Podcasts & MP3s on Renal function • Videos on Renal function
Evidence Based Medicine Regarding Renal functionCochrane Collaboration on Renal function • Bandolier on Renal function • TRIP on Renal function
Cost Effectiveness of Renal functionCost Effectiveness of Renal function
Clinical Trials Involving Renal functionOngoing Trials on Renal function at Clinical Trials.gov • Trial results on Renal function • Clinical Trials on Renal function at Google
Guidelines / Policies / Government Resources (FDA/CDC) Regarding Renal functionUS National Guidelines Clearinghouse on Renal function • NICE Guidance on Renal function • NHS PRODIGY Guidance • FDA on Renal function • CDC on Renal function
Textbook Information on Renal functionBooks and Textbook Information on Renal function
Pharmacology Resources on Renal functionDosing of Renal function • Drug interactions with Renal function • Side effects of Renal function • Allergic reactions to Renal function • Overdose information on Renal function • Carcinogenicity information on Renal function • Renal function in pregnancy • Pharmacokinetics of Renal function •
Genetics, Pharmacogenomics, and Proteinomics of Renal functionGenetics of Renal function • Pharmacogenomics of Renal function • Proteomics of Renal function
Newstories on Renal functionRenal function in the news • Be alerted to news on Renal function • News trends on Renal function
Commentary on Renal functionBlogs on Renal function
Patient Resources on Renal functionPatient resources on Renal function • Discussion groups on Renal function • Patient Handouts on Renal function • Directions to Hospitals Treating Renal function • Risk calculators and risk factors for Renal function
Healthcare Provider Resources on Renal functionSymptoms of Renal function • Causes & Risk Factors for Renal function • Diagnostic studies for Renal function • Treatment of Renal function
Continuing Medical Education (CME) Programs on Renal functionCME Programs on Renal function
International Resources on Renal functionRenal function en Espanol • Renal function en Francais
Business Resources on Renal functionRenal function in the Marketplace • Patents on Renal function
Informatics Resources on Renal functionList of terms related to Renal function
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Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .

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