Renal function
In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology.
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2 Glomerular filtration rate 3 Cockroft-Gault formula 4 Children: Schwartz |
Indirect markers
Most doctors use creatinine, urea and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease.
Glomerular filtration rate
In known 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. GFR measurements can aid a nephrologist in deciding when to initiate dialysis or renal transplantation.
Very often, the GFR is expressed as ml/min/1.7 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, which can be calculated on the basis of weight and height.
Cockroft-Gault formula
A commonly used surrogate marker for actual creatinine clearance is the Cockroft-Gault formula, which employs creatinine measurements and a patient's weight to predict the clearance.
The formula is:
It is named after the scientists who first published the formula in: Cockroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron 1976;16:31-42.
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. An online calculator[1] warns that the result may overstate the GFR.