Measurement of GFR

GFR is calculated as the clearance of exogenous filtration indicators, such as inulin, iohexol, iothalamate, technetium 99m diethylenetriamine pentaacetic acid, and chromium 51-ethylenediamine tetraacetic acid, which are exclusively removed via glomerular filtration. In order to accurately calculate the clearance curve using plasma clearance techniques, patients must stay inpatient or in the clinic for several hours. As a result, GFR measurements using these techniques remain impractical and expensive with common methodologies (e.g., iohexol or inulin by plasma clearance or nuclear renal scans), and are not frequently carried out in clinical practice or large-scale clinical research.

Consequently, endogenous filtration indicators are frequently used to determine GFR. Patients at risk of developing early renal disease when GFR is normal to raised would benefit from having their GFR evaluated using more exact and precise methods, even though estimated GFR is often sufficient for clinical decision making, especially when GFR is < 60 ml/min/1.73m². Due to the possibility of early therapies intended to stop the progression of kidney disease, the early detection of diminishing renal function may be crucial. Early intervention is one justification for the Preventing Early Renal Loss (PERL) Study, whose endpoint changes in GFR as determined by iohexol. Therefore, precise and accurate diagnostic methods used in a clinical environment are required to identify kidney disease in its early stages.

Inulin, which has been used for decades as the gold-standard measure of GFR, is one of many ways to measure GFR. To achieve the optimum outcomes, inulin must be collected through urine collection or continuously infused, both of which provide substantial challenges for its widespread use. There are a number of radioisotopes, including ⁹⁹mTc-DTPA, ⁵¹Cr-EDTA, and ¹²⁵Iothalamate, but their application outside of research investigations is difficult due to logistics, expense, and radiation exposure, especially in asymptomatic young adults and/or adolescents. The kidney does not absorb, metabolize, or produce iohexol or non-radioactive iothalamate, which are nonionic, low osmolar contrast agents. Low toxicity for iohexol has been observed in radiology practice (contrast x-rays), where dosages 10–50 times larger than those required for GFR assessment are employed. In the Prevent Early Renal Loss (PERL) project, our institutions have safely measured GFR by iohexol clearance over 1000 times without any problems. In fact, for more than 20 years, publications have asserted that the gold-standard GFR measurement is iohexol. In 2226 research participants between 2011 and 2016, the Advanced Research and Diagnostic Laboratory at the University of Minnesota effectively assessed iohexol to evaluate GFR.

Decreased GFR

A low GFR indicates that your kidneys aren’t properly filtering your blood.

You have renal disease if your GFR is less than 60. You have renal failure and will need dialysis or a kidney transplant if the number is less than 15.

Chronic Kidney Disease (CKD)

The function of your kidneys is described by the five phases of CKD. With time, kidney disease can worsen. Your kidneys are still able to filter waste out of your blood throughout the early stages (Stages 1-3). Your kidneys may stop functioning entirely and must work harder to filter your blood in the latter stages (Stages 4-5).

At every stage of CKD, you should take action to slow down kidney damage and prolong the time that your kidneys are able to function.

• Stage 1 of CKD: If your eGFR is normal or over 90, you have stage 1 CKD, which means your kidneys have just minor damage. It’s possible that you are symptom-free because your kidneys are still functioning properly. In addition to protein in your urine, you might exhibit other kidney disease symptoms.
• Stage 2 of CKD: If you have stage 2 CKD, your eGFR has decreased to between 60 and 89 and you have modest renal damage. Since your kidneys often function normally, you might not experience any symptoms. Other symptoms of kidney impairment could include bodily harm or protein in your urine.
• Stage 3 of CKD: If you have stage 3 CKD, your eGFR is between 30 and 59 and your kidney damage is modest to moderate. Your kidneys do not filter trash and extra fluid from your blood as effectively as they should. The accumulation of this waste in your body can lead to various health issues like high blood pressure and bone damage. Your hands or feet could swell, and you could start to feel weak and exhausted.
  Depending on your eGFR, stage 3 CKD is divided into two substages:
  • You are in stage 3a if your eGFR is between 45 and 59.
  • You are in stage 3b if your eGFR is between 30 and 44.

Many Stage 3 patients who receive therapy and make healthy lifestyle adjustments do not go to Stage 4 or Stage 5.

• Stage 4 of CKD: If you have stage 4 CKD, your eGFR is between 15 and 29, and your kidneys have suffered moderate to severe damage. Your kidneys’ ability to filter waste from your blood is not as good as it could be. Your body may accumulate this waste, which could lead to heart disease, high blood pressure, and other health issues like bone and heart disease. You’ll probably have symptoms including lower back ache and hand and foot swelling.  This is the last stage before kidney failure. To prevent kidney deterioration and prepare for potential therapies for kidney failure, it is crucial to schedule regular appointments with a nephrologist (kidney specialist).
• Stage 5 of CKD: If you have stage 5 CKD, your eGFR is less than 15 and your kidneys have suffered significant damage. Your kidneys are either already failing or are very near to failing (stopped working). Waste products accumulate in your body as a result of your kidneys’ inability to filter waste from your blood, which can make you very ill and result in various health issues. Dialysis or a kidney transplant are two possibilities for treatment when your kidneys fail.

FAQs on Glomerular Filtration Rate

Question 1: What is the filtration membrane, how does it work, and what materials does it consist of?

Answer:

A filter is a  barrier between the blood and the glomerular capsule’s interior.

Consists of 3 layers:

1. Endothelium with fenestration.
2. The capsule of the glomerulus’ visceral membrane.
3. The basement membrane, which is made up of the basal laminae of the other two layers fused together.

Question 2: What is a glomerular filtration rate (GFR) test?

Answer:

A blood test called a glomerular filtration rate (GFR) measures how well your kidneys are functioning. Glomeruli are little filters found in your kidneys. These filters aid in clearing the blood of waste and extra fluid. How much blood flows through these filters each minute is determined by a GFR test.

A GFR can be directly assessed, however, it is a challenging procedure that needs skilled experts. As a result, the most common method for estimating GFR is the estimated GFR test or eGFR. Your provider will employ a technique called a GFR calculator to obtain an estimate. A formula that calculates the rate of filtration is known as a GFR calculator.

Question 3: What is the use of the GFR test?

Answer:

When kidney illness is most easily treated, an early diagnosis is made with the aid of a GFR test. A person with chronic kidney disease (CKD) or another disorder that damages the kidneys may also be monitored using GFR. These include hypertension and diabetes.

Question 4: What is impermeable to the glomerular filter?

Answer:

Due to the effects of the glomerular capillary filtration membrane’s size barrier and charge barrier, heavy molecular weight proteins in the plasma (such as albumin and globulin) cannot normally pass through the filtration membrane.

Question 5: What kind of filtration does the glomerulus employ?

Answer:

Renal ultrafiltration is the method by which glomerular filtration takes place. The filtrate is pushed out of the capillaries and into the slits in the nephron by the force of hydrostatic pressure in the glomerulus, which is the force of pressure produced from the pressure of the blood artery itself.

Question 6: What is necessary for glomerular filtration?

Answer:

Glomerular filtration is dependent on the same opposing forces—hydrostatic pressure and oncotic pressure, together known as Starling’s forces—that cause the fluid exchange in every capillary in our body.

The kidneys are two reddish-brown, bean-shaped organs found in vertebrates. They are located on the left and right sides of the retroperitoneal space in adults and are about 12 centimeters long. They have paired renal arteries and veins that carry blood into and out of them. Each kidney has a ureter, a tube that carries urine from the kidneys to the bladder.

The kidney takes involved in the regulation of toxin elimination, fluid osmolality, acid-base balance, various electrolyte concentrations, and volume of various body fluids. One-fifth of the blood volume that enters the kidneys is filtered in the glomerulus, where filtering takes place. Amino acids, salt, bicarbonate, glucose, and solute-free water are a few examples of compounds that are reabsorbed. Hydrogen, ammonium, potassium, and uric acid are a few examples of chemicals that are released. The structural and operational unit of the kidney is the nephron. A mouse kidney only has about 12,500 nephrons, compared to the roughly 1 million seen in an adult human kidney. Additionally, the kidneys perform tasks that are not dependent on the nephrons. For instance, they produce the hormones erythropoietin and renin, as well as the conversion of a precursor of vitamin D into its active form, calcitriol.