What is GFR?
March 1, 2012
GFR - glomerular filtration rate is the best test to measure your level of kidney function and determine your stage of kidney disease. Your doctor can calculate it from the results of your blood creatinine test, your age, race, gender and other factors.
The earlier kidney disease is detected, the better the chance of slowing or stopping its progression.
What happens if my test results show I may have chronic kidney disease?
Your doctor will want to pinpoint your diagnosis and check your kidney function to help plan your treatment. The doctor may do the following:
- Calculate your Glomerular Filtration Rate (GFR), which is the best way to tell how much kidney function you have. You do not need to have another test to know your GFR. Your doctor can calculate it from your blood creatinine, your age, race, gender and other factors. Your GFR tells your doctor your stage of kidney disease and helps the doctor plan your treatment. (See chart "Stages of Chronic Kidney Disease.")
- Perform an ultrasound or CT scan to get a picture of your kidneys and urinary tract. This tells your doctor whether your kidneys are too large or too small, whether you have a problem like a kidney stone or tumor and whether there are any problems in the structure of your kidneys and urinary tract.
- Perform a kidney biopsy, which is done in some cases to check for a specific type of kidney disease, see how much kidney damage has occurred and help plan treatment. To do a biopsy, the doctor removes small pieces of kidney tissue and looks at them under a microscope.
Your doctor may also ask you to see a kidney specialist who will consult on your case and help manage your care.
Understanding your lab values
People who develop chronic kidney disease may have some or all of the following tests and measurements. If you have kidney disease ask your doctor which tests you will have and how often they will be done. Speak to your doctor about your results. If your numbers are not in the normal range, ask how to improve them.
Serum Creatinine: Creatinine is a waste product in your blood that comes from muscle activity. It is normally removed from your blood by your kidneys, but when kidney function slows down, the creatinine level rises. Your doctor should use the results of your serum creatinine test to calculate your GFR.
Glomerular Filtration Rate (GFR): Your GFR tells how much kidney function you have. It may be estimated from your blood level of creatinine. If your GFR falls below 30 you will need to see a kidney disease specialist (called a nephrologist), Your kidney doctor will speak to you about treatments for kidney failure like dialysis or kidney transplant. A GFR below 15 indicates that you need to start one of these treatments.
Blood Urea Nitrogen (BUN): Urea nitrogen is a normal waste product in your blood that comes from the breakdown of protein from the foods you eat and from your body metabolism. It is normally removed from your blood by your kidneys, but when kidney function slows down, the BUN level rises. BUN can also rise if you eat more protein, and it can fall if you eat less protein.
Urine Protein: When your kidneys are damaged, protein leaks into your urine. A simple test can be done to detect protein in your urine. Persistent protein in the urine is an early sign of chronic kidney disease.
Microalbuminuria: This is a sensitive test that can detect a small amount of protein in the urine.
Urine Creatinine: This test estimates the concentration of your urine and helps to give an accurate protein result.
Protein-to-Creatinine Ratio: This estimates the amount of protein you excrete in your urine in a day and avoids the need to collect a 24-hour sample of your urine.
Serum Albumin: Albumin is a type of body protein made from the protein you eat each day. A low level of albumin in your blood may be caused by not getting enough protein or calories from your diet. A low level of albumin may lead to health problems such as difficulty fighting off infections. Ask your dietitian how to get the right amount of protein and calories from your diet.
nPNA: Your nPNA (normalized protein nitrogen appearance) is a test that may tell if you are eating enough protein. This measurement comes from lab studies that include a urine collection and blood work. Your dietitian may ask for an accurate food record to go with this test.
Subjective Global Assessment (SGA): Your dietitian may use SGA to help check for signs of nutrition problems. The dietitian will ask you some questions about your daily diet and check your weight and the fat and muscle stores in your face, hands, arms, shoulders and legs. Ask your dietitian about your score on the SGA. If your score is too low, ask how to improve it.
Hemoglobin: Hemoglobin is the part of red blood cells that carries oxygen from your lungs to all parts of your body. Your hemoglobin level tells your doctor if you have anemia, which makes you feel tired and have little energy. If you have anemia, you may need treatment with iron supplements and a hormone called erythropoietin (EPO). The goal of anemia treatment is to reach and maintain a hemoglobin level of at least 11 to 12.
Hematocrit: Your hematocrit is a measure of the red blood cells your body is making. A low hematocrit can mean you have anemia and need treatment with iron and EPO. You will feel less tired and have more energy when your hematocrit reaches at least 33 to 36 percent.
TSAT and Serum Ferritin: Your TSAT (pronounced tee-sat) and serum ferritin (pronounced ferry-tin) are measures of iron in your body. Your TSAT should be above 20 percent and your serum ferritin should be above 100. This will help you build red blood cells. Your doctor will recommend iron supplements when needed to reach your target levels.
Parathyroid Hormone (PTH): High levels of parathyroid hormone (PTH) may result from a poor balance of calcium and phosphorus in your body. This can cause bone disease. Ask your doctor if your PTH level is in the right range. Your doctor may order a special prescription form of vitamin D to help lower your PTH. Caution: Do not take over-the-counter vitamin D unless ordered by your doctor.
Calcium: Calcium is a mineral that is important for strong bones. Ask your doctor what your calcium level should be. To help balance the amount of calcium in your blood, your doctor may ask you to take calcium supplements and a special prescription form of vitamin D. Take only the supplements and medications recommended by your doctor.
Phosphorus: A high phosphorus level can lead to weak bones. Ask your doctor what your phosphorus level should be. If your level is too high, your doctor may ask you to reduce your intake of foods that are high in phosphorus and take a type of medication called a phosphate binder with your meals and snacks.
Potassium: Potassium is a mineral in your blood that helps your heart and muscles work properly. A potassium level that is too high or too low may weaken muscles and change your heartbeat. Whether you need to change the amount of high- potassium foods in your diet depends on your stage of kidney disease. Ask your doctor what your potassium level should be. Your dietitian can help you plan your diet to get the right amount of potassium.
Body Weight: Maintaining a healthy weight is important to your overall health. If you are losing weight without even trying, you may not be getting the right nutrition to stay healthy. Your dietitian can suggest how to safely add extra calories to your diet if needed. On the other hand, if you are slowly gaining too much weight, you may need to reduce calories and increase your activity level. A sudden weight gain can also be a problem. If it is accompanied by swelling, shortness of breath and a rise in blood pressure, it may be a sign of too much fluid in your body. Speak to your doctor if your weight changes noticeably.
Blood Pressure: Ask your doctor what your blood pressure should be. If your blood pressure is high, make sure to follow all the steps in your prescribed treatment, which may include taking high blood pressure medications, cutting down on the amount of salt in your diet, losing excess weight and following a regular exercise program.
Total Cholesterol: Cholesterol is a fat-like substance found in your blood. A high cholesterol level may increase your chance of having heart and circulation problems. For many patients, a good level for total cholesterol is below 200. If your cholesterol level is too high, your doctor may ask you to make some changes in your diet and increase your activity level. In some cases, medications are also used.
LDL Cholesterol: LDL cholesterol is a type of "bad" cholesterol. A high LDL level may increase your chance of having heart and circulation problems. For many patients, the target level for LDL cholesterol is below 100. If your LDL level is too high, your doctor may ask you to make some changes in your diet and increase your activity level.
Triglyceride: Triglyceride is a type of fat found in your blood. A high triglyceride level along with high levels of total and LDL cholesterol may increase your chance of heart and circulation problems.