Questions For Your Doctor About Test Results
Your doctor can help you understand the significance of an eGFR test for your overall health. Some questions that can help you discuss your results with your doctor include:
- What was my eGFR test result? Is that considered normal or abnormal?
- What does this test result indicate about my kidney function?
- How was my GFR estimated? Is that estimation method accurate in my situation?
- Is any other test warranted to calculate eGFR again or to directly measure GFR?
- Do you suggest any follow-up tests?
What Can I Expect If I Have Kidney Disease
If you have kidney disease you can still live a productive home and work life and enjoy time with your family and friends. To have the best outcome possible, its important for you to become an active member of your treatment team.
Early detection and appropriate treatment are important in slowing the disease process, with the goal of preventing or delaying kidney failure. You will need to keep your medical appointments, take your medications as prescribed, stick to a healthy diet and monitor your blood pressure and blood sugar.
Does Exercise Increase Blood Flow To The Kidneys
Exercise induces profound changes in the renal haemodynamics and in electrolyte and protein excretion. Effective renal plasma flow is reduced during exercise. The reduction is related to the intensity of exercise and renal blood flow may fall to 25% of the resting value when strenuous work is performed.
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Keeping Your Kidneys Healthy
Well-functioning kidneys are essential to your overall health. Early detection of kidney disease can be life-saving. Medication and changes to lifestyle, along with an early referral to a kidney specialist, can prevent or delay kidney failure.
If you are at increased risk of chronic kidney disease, talk to your doctor about having a regular kidney health check.
Gross Anatomy Of The Kidney
There are normally two separate kidneys each with its own fibrous capsule. They are located in a retroperitoneal location in the upper abdomen, one in each paravertebral gutter adjacent to T12 to L3. They are approximately 12cm long and weigh 150 grams each. The right kidney is slightly lower than the left due to the presence of the liver in the right upper abdomen. The upper part of each kidney is protected posteriorly by the 11th and 12th ribs.
The kidney has two distinct regions a cortex around the outer edge, and an inner medulla. The medulla is composed of numerous renal pyramids. At the innermost ends of the pyramids are calyces which receive urine, which then drain to the renal pelvis and the ureter.
Figure 1. Diagram showing renal cortex and medulla
The basic functional unit of the kidney is the nephron . Each kidney contains approximately 1 1.5 million nephrons. Each nephron is basically a folded up tube situated proximally is a complex capillary network and capsule where plasma is filtered , which produces the glomerular filtrate, and situated distally are the collecting ducts from which urine drains. Between Bowmans capsule and the collecting duct is the proximal convoluted tubule , the loop of Henle and the distal tubule, each of which serve specific functions. The nephrons are all orientated such that the glomerulus and Bowmans capsule lie in the cortex with their loop of Henle and collecting duct pointing towards and entering the medulla.
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Pressure Relationships In The Venous System
Although vessel diameter increases from the smaller venules to the larger veins and eventually to the venae cavae , the total cross-sectional area actually decreases. The individual veins are larger in diameter than the venules, but their total number is much lower, so their total cross-sectional area is also lower.
Also notice that, as blood moves from venules to veins, the average blood pressure drops, but the blood velocity actually increases. This pressure gradient drives blood back toward the heart. Again, the presence of one-way valves and the skeletal muscle and respiratory pumps contribute to this increased flow. Since approximately 64 percent of the total blood volume resides in systemic veins, any action that increases the flow of blood through the veins will increase venous return to the heart. Maintaining vascular tone within the veins prevents the veins from merely distending, dampening the flow of blood, and as you will see, vasoconstriction actually enhances the flow.
When Should I Get An Egfr Test
There are a number of circumstances in which an eGFR test may be appropriate and beneficial for your medical care.
An eGFR test can help identify serious kidney disease and kidney failure. In response to a wide range of symptoms, an eGFR test can help determine if your kidneys are working properly.
Sometimes kidney disease does not cause immediate symptoms. In these cases, testing with eGFR may enable an earlier diagnosis and improved ability to slow the progression of the disease. In general, this type of screening with an eGFR test is only done in people who have an elevated risk of kidney problems.
When you have previously been diagnosed with kidney disease or have had abnormal eGFR tests, doing one or more repeat tests may aid in the diagnosis and monitoring of your condition.
In some cases, an eGFR test is conducted before kidney donation or the initiation of certain medical treatments or procedures. In some of these circumstances, though, a more precise test may be necessary to directly measure rather than estimate GFR.
Your doctor is in the best position to address whether an eGFR test or any other test of kidney function is appropriate for you given your overall health and health history.
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Measurement Of Blood Pressure
Blood pressure is one of the critical parameters measured on virtually every patient in every healthcare setting. The technique used today was developed more than 100 years ago by a pioneering Russian physician, Dr. Nikolai Korotkoff. Turbulent blood flow through the vessels can be heard as a soft ticking while measuring blood pressure these sounds are known as Korotkoff sounds. The technique of measuring blood pressure requires the use of a sphygmomanometer and a stethoscope. The technique is as follows:
- The clinician wraps an inflatable cuff tightly around the patients arm at about the level of the heart.
- The clinician squeezes a rubber pump to inject air into the cuff, raising pressure around the artery and temporarilycutting off blood flow into the patients arm.
- The clinician places the stethoscope on the patients antecubital region and, while gradually allowing air within the cuff to escape, listens for the Korotkoff sounds.
Figure 3. When pressure in a sphygmomanometer cuff is released, a clinician can hear the Korotkoff sounds. In this graph, a blood pressure tracing is aligned to a measurement of systolic and diastolic pressures.
The majority of hospitals and clinics have automated equipment for measuring blood pressure that work on the same principles. An even more recent innovation is a small instrument that wraps around a patients wrist. The patient then holds the wrist over the heart while the device measures blood flow and records pressure .
Kidneys Are A Filter System
The main job of the kidneys is to remove waste from the blood and return the cleaned blood back to the body. Each minute about one litre of blood one-fifth of all the blood pumped by the heart enters the kidneys through the renal arteries. After the blood is cleaned, it flows back into the body through the renal veins.
Each kidney contains about one million tiny units called nephrons. Each nephron is made up of a very small filter, called a glomerulus, which is attached to a tubule. As blood passes through the nephron, fluid and waste products are filtered out. Much of the fluid is then returned to the blood, while the waste products are concentrated in any extra fluid as urine .
The urine flows through a tube called the ureter into the bladder. Urine passes from the bladder out of the body through a tube called the urethra. The kidney usually makes one to two litres of urine every day depending on your build, how much you drink, the temperature and the amount of exercise you do.
A healthy kidney can greatly increase its work capacity. With two healthy kidneys, each kidney performs 50 per cent of the normal kidney function. If one kidney is lost, the other kidney can enlarge and provide up to 75 per cent of the normal kidney function .
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What Else Do Kidneys Do
Kidneys are always busy. Besides filtering the blood and balancing fluids every second during the day, the kidneys constantly react to hormones that the brain sends them. Kidneys even make some of their own hormones. For example, the kidneys produce a hormone that tells the body to make red blood cells.
Now you know what the kidneys do and how important they are. Maybe next Valentine’s Day, instead of the same old heart, you can give your parents a special card featuring the kidneys!
The Role Of Venoconstriction In Resistance Blood Pressure And Flow
As previously discussed, vasoconstriction of an artery or arteriole decreases the radius, increasing resistance and pressure, but decreasing flow. Venoconstriction, on the other hand, has a very different outcome. The walls of veins are thin but irregular thus, when the smooth muscle in those walls constricts, the lumen becomes more rounded. The more rounded the lumen, the less surface area the blood encounters, and the less resistance the vessel offers. Vasoconstriction increases pressure within a vein as it does in an artery, but in veins, the increased pressure increases flow. Recall that the pressure in the atria, into which the venous blood will flow, is very low, approaching zero for at least part of the relaxation phase of the cardiac cycle. Thus, venoconstriction increases the return of blood to the heart. Another way of stating this is that venoconstriction increases the preload or stretch of the cardiac muscle and increases contraction.
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What Is Kidney Transplantation
Kidney transplantation involves placing a healthy kidney into your body where it can perform all of the functions that a failing kidney cant. Kidneys for transplantation come from two sources: living donors and deceased donors. Living donors are usually immediate family members or sometimes spouses. This is possible because a person can live well with one healthy kidney.
Blood Flow During Exercise
Blood flow within muscles fluctuates as they contract and relax. During contraction, the vasculature within the muscle is compressed, resulting in a lower arterial inflow with inflow increased upon relaxation. The opposite effect would be seen if measuring venous outflow.
This rapid increase and decrease in flow is observed over multiple contractions. If the muscle is used for an extended period, mean arterial inflow will increase as the arterioles vasodilate to provide the oxygen and nutrients required for contraction. Following the end of contractions, this increased mean flow remains to resupply the muscle tissue with required nutrients and clear inhibitory waste products, due to the loss of the inhibitory contractile phase.
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Vessel Length And Diameter
The length of a vessel is directly proportional to its resistance: the longer the vessel, the greater the resistance and the lower the flow. As with blood volume, this makes intuitive sense, since the increased surface area of the vessel will impede the flow of blood. Likewise, if the vessel is shortened, the resistance will decrease and flow will increase.
The length of our blood vessels increases throughout childhood as we grow, of course, but is unchanging in adults under normal physiological circumstances. Further, the distribution of vessels is not the same in all tissues. Adipose tissue does not have an extensive vascular supply. One pound of adipose tissue contains approximately 200 miles of vessels, whereas skeletal muscle contains more than twice that. Overall, vessels decrease in length only during loss of mass or amputation. An individual weighing 150 pounds has approximately 60,000 miles of vessels in the body. Gaining about 10 pounds adds from 2000 to 4000 miles of vessels, depending upon the nature of the gained tissue. One of the great benefits of weight reduction is the reduced stress to the heart, which does not have to overcome the resistance of as many miles of vessels.
How Is Estimating Gfr Different From Measuring Gfr
There are different ways to assess the glomerular filtration rate, and estimating GFR is distinct from directly measuring GFR.
Measuring GFR is possible by infusing a substance, such as a compound called inulin or certain radioisotopes, into the blood and seeing how quickly it is cleared by the kidneys. While more accurate, this type of testing is expensive and requires more specialization, reducing its ability to serve as a widespread method of assessing kidney function.
Accordingly, direct GFR measurement is reserved for particular situations, and tests that estimate GFR based on creatinine or cystatin C are much more frequently used.
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Can I Take The Test At Home
Although most kidney function testing is prescribed by a doctor and carried out in a medical facility, some at-home options exist for eGFR testing.
With at-home kits, only the sample collection occurs at home. Once a sample is taken, it must be sent to a laboratory where it can be analyzed, and results are made available electronically.
At-home tests generally do not provide direct medical consultation and interpretation of your results, so the test report will normally need to be discussed with your doctor.
What Color Is Your Urine When Your Kidneys Are Shutting Down
When kidneys are failing, the increased concentration and accumulation of substances in urine lead to a darker color which may be brown, red or purple. The color change is due to abnormal protein or sugar, high levels of red and white blood cells, and high numbers of tube-shaped particles called cellular casts.
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Renal Blood Flow And Filtration Fraction
Renal blood flow has been estimated in human fetuses using color pulsed wave Doppler ultrasonography.10 The method was previously validated by the same authors in studies of the fetal lamb,11 in which estimates obtained by this technique agreed closely with those made using a perivascular flow probe placed directly around the renal artery. In the human fetuses, they obtained mean values for two kidneys of 40 mL/min at 22 weeks gestation, 80 mL/min at 30 weeks, and 130 mL/min at 36 weeks. This amounted to 6.8%, 5.2%, and 5.2%, respectively, of the simultaneously determined cardiac output, figures that compare reasonably well with values of 4.9% and 3.2% obtained in immature and mature baboon fetuses, respectively. However, this estimate of human fetal RBF seems remarkably high, given that RBF measured directly by renal vein catheterization in two infants during the first 2 weeks of extrauterine life was in the range of 30 to 50 mL/min.12 Furthermore, if these estimates for RBF are combined with those calculated for fetal GFR, the filtration fraction would be approximately 1% at 22 weeks, 1.8% at 30 weeks, and 2.3% at 36 weeks, very low compared with all available measurements in children and adults . It therefore seems prudent to regard this report of fetal RBF as provisional until it is confirmed by further studies.
Jan C. ter Maaten, Fatiu A. Arogundade, in, 2010
Are Test Results Accurate
An eGFR test is a straightforward and generally accurate method of assessing kidney function. In the United States, efforts to calibrate and standardize creatinine measurements have improved the dependability of using creatinine levels to estimate GFR.
However, eGFR is not a perfect test, and several factors can affect its accuracy. For example, eGFR calculations based on creatinine levels are only accurate when a person has stable kidney function. The test is generally not useful or recommended in patients with acute illness, including many who are hospitalized or have serious co-existing conditions.
In addition, most eGFR tests are based on creatinine levels, and test accuracy is affected by individual factors that can influence creatinine levels and the calculation of eGFR. Some of these factors include:
To reduce the effects of these individual factors, eGFR may be estimated by measuring a substance called cystatin C instead of creatinine. In some cases, two eGFR calculationsone using creatinine and one using cystatin C or a combination of bothmay be performed. This serves as a type of initial and confirmatory testing that may improve overall accuracy of estimating GFR.
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Measuring How Your Kidneys Work
It is difficult to calculate the exact rate at which your kidneys work. The best measure of kidney function is called the glomerular filtration rate . The GFR can be estimated using a mathematical formula. This formula uses the level of creatinine in your blood to estimate how well your kidneys are filtering waste from your blood. It can indicate if there is any kidney damage.
The higher the filtration rate, the better the kidneys are working. A GFR of 100 mL/min/1.73 m2 is in the normal range. This is about equal to 100 per cent kidney function. Based on this measurement system, a GFR of 50 mL/min/1.73 m2 could be called 50 per cent kidney function and a GFR of 30 mL/min/1.73 m2 could be called 30 per cent kidney function.
If your doctor orders a blood test to learn more about your kidney function, an eGFR result is provided automatically, along with your creatinine results.
Your doctor may also test for other signs and conditions that may indicate you have chronic kidney disease. These may include tests for:
- protein in your urine
- blood in your urine
- high blood pressure
Taking An Estimated Glomerular Filtration Rate Test
An estimated glomerular filtration rate test is a type of blood test. The blood sample for the test is taken with a needle that is inserted into a vein in your arm. This routine procedure is usually done at a doctors office, hospital, or laboratory.
For an at-home test, a drop of blood must be taken from your fingertip and applied to a test strip that can be sent to a medical laboratory.
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