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How to Calculate Glomerular Filtration Rate

written by: Leigh A. Zaykoski•edited by: Leigh A. Zaykoski•updated: 2/26/2010

Doctors use a patient’s glomerular filtration rate to determine how well the kidneys are functioning. Learn how to calculate glomerular filtration rate and better understand how this calculation relates to your health.

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    Glomerular Filtration Rate

    Glomerular filtration rate is a measure of how well the kidneys are functioning. In someone with kidney disease, glomerular filtration rate indicates how far kidney function has declined. Doctors use this measurement in treating and monitoring cases of acute renal failure, chronic kidney disease, and end-stage renal failure.

    Normal glomerular filtration rate is 90 mL/min, with an increased risk for kidney disease if other risk factors for kidney disorders exist. These factors include high blood pressure, diabetes, family history and advanced age. The National Kidney Foundation indicates that a GFR of more than 90 with protein in the urine indicates stage one kidney disease. Stage two kidney disease causes a GFR of 60 to 89 mL/min. When GFR decreases to 30 to 59, mL/min, the patient has stage three kidney disease. Stage four kidney disease results in a GFR of 15 to 29. A GFR of less than 15 mL/min indicates renal failure, with hemodialysis or a kidney transplant required to filter wastes out of the blood and preserve the patient’s life.

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    How to Calculate Glomerular Filtration Rate

    Doctors use several complicated formulas to calculate a person’s GFR. If you want to know how to calculate glomerular filtration rate, you’ll need several pieces of information. This information includes your age, race, gender, and serum creatinine level.

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    Creatinine Blood Test

    In order to know your serum creatinine level, you’ll need to have a blood test known as the basic metabolic panel. This blood test determines the levels of eight substances in the blood. These substances include potassium, sodium, calcium, glucose, chloride, carbon dioxide, blood urea nitrogen (BUN), and creatinine. BUN and creatinine are waste products that form during the breakdown of proteins in the body. When the kidneys function properly, they eliminate these waste products from the blood and prevent accumulation of harmful wastes. When kidney function decreases, the kidneys do not filter these waste products and they build up in the blood.

    The National Institutes of Health reports that normal serum creatinine levels range from 0.8 to 1.4 mg/dL. As these levels increase, glomerular filtration rate decreases.

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    How to Increase GFR

    If your doctor determines that you have kidney disease, a renal diet and other treatments may help improve your kidney function and increase your glomerular filtration rate. The renal diet restricts the intake of foods that make the kidneys work harder or result in the buildup of waste products in the blood. Your doctor will work with you to develop a diet plan that matches your condition. Someone with stage one kidney disease may not need any dietary restrictions, while someone with renal failure has to restrict the intake of fluids, sodium, phosphorus, potassium and protein.

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    Effects of Low GFR

    As your glomerular filtration rate decreases, you may begin to feel ill. As creatinine and other waste products accumulate in the blood, they cause fatigue, itchy skin, nausea, vomiting, and other effects. Your kidneys may not maintain normal fluid and electrolyte balances in the body, leading to swelling of the extremities and feelings of malaise.

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    References

    National Kidney Foundation: Glomerular Filtration Rate

    National Institutes of Health: Creatinine - Blood