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What is the Glomerular Filtration Rate (GFR)?

The glomerular filtration rate (GFR) is a test used to assess how well the kidneys are performing. It measures how much blood passes through the glomeruli (tiny kidney filters), i.e. kidneys’ ability to filter and excrete all metabolic waste products from the body. GFR is probably the best indicator of renal function and functional mass assessment. The estimates are used to detect the stage of CKD, assess its severity and monitor progress. When a clear picture of the patients’ renal condition is obtained, treatment methods can be decided. The earlier kidney disease is detected, the better the chances are of slowing down its progression.

How is GFR estimated?

The calculation of glomerular filtration rate is done through various methods such as:

  • measurement of creatinine in plasma,
  • determination of creatinine clearance after 24-hour urine collection and appropriate calculations, and
  • most accurately, by radionucleotide methods

In everyday practice, the level of GFR can also be estimated by equations, taking into account the level of creatinine in blood (SCr) and variables like age, gender, body size and ethnicity.

One of the earliest GFR calculations is the Cockcroft-Gault creatinine clearance formula, which accounts for age, sex and muscle mass.

What is a normal GFR number?

For adults, the normal GFR number is above 90. However, with age GFR declines even in people not suffering from kidney disease.

Age (years) Average estimated GFR
20 – 29 116
30–39 107
40–49 99
50–59 93
60–69 85
70+ 75

Stages of chronic kidney disease, based on estimated GFR

Stage GFR Kidney Function
Stage 1 90 and higher Kidney damage with normal kidney function View more
Stage 2 60 to 89 Kidney damage with mild loss of kidney function View more
Stage 3 30 to 59 Kidney damage with moderate decrease in kidney function View more
Stage 4 15 to 29 Kidney damage with severe reduction of kidney function View more
Stage 5 Less than 15 or dialysis End-stage renal failure View more

Stage 1

In the early stages of CKD (1-2) the patient is asymptomatic, the level of creatinine in blood is normal (or close to normal) and fluid, acid-base and electrolyte balance are maintained by adaptive function increase in the remaining nephrons. In stage 1, where the GFR is normal but there are signs of kidney damage, like albuminuria (an abnormal loss of albumin in the urine). It is very important to get the diagnosis and proceed to treatment early, in order to slow down or even revert the course of CKD.

Stage 2

In terms of kidney function and manifestations, it is similar to stage 1. It is also important to assess the progression of CKD, since the remaining nephrons can still preserve the homeostasis of the human body and there might not be any symptoms. In this stage, the GFR decline rate should be evaluated. For example, a rate of 4ml/min per year means that if the progression of CKD cannot be delayed, the patient will reach the stage of kidney failure in 11 years and will need renal replacement therapy.

Stage 3

In stage 3, patients usually still have no symptoms, but their levels of SCr, erythropoietin, calcitriol and parathyroid hormones are abnormal. During this moderate kidney impairment stage, the human homeostasis is starting to lose its balance, so it is crucial to evaluate and treat complications (hypertension, anemia, possible bone disease etc). The most essential features of stage 3 management are:

  • Tight control of blood pressure within target level: (130 mmhg systolic and 80mmhg diastolic).

    Most patients will require more than two drugs to reach this target level of blood pressure, most importantly a diuretic and also a calcium channel blocker.

    For all diabetics with CKD and patients with albuminuria, ACE inhibitors are the antihypertensive drugs of choice. As found in large trials, this drug category can delay the progression of CKD in these special groups of patients.
  • Tight glycemic control for diabetics
  • Dietary protein restriction
  • Smoking cessation
  • Lipid lowering therapy

Stage 4

In stage 4 patients may have symptoms like anaemia, bone disease, hypertension, cardiovascular complications, hypocalcaemia, neuropathy, malnutrition, hyperphosphatemia, hyperkalemia, anorexia, and acidosis. At this stage of severe kidney impairment, you are advised to see a nephrologist, start considering dialysis and get ready for the process. Click here to learn about dialysis.

Stage 5

In stage 5 the kidneys have failed, so renal replacement therapy is required i.e. hemodialysis, peritoneal dialysis or kidney transplantation. Possible symptoms are cardiovascular issues, anorexia, nausea or vomiting, resistant hyperkalemia, etc. After your screening, your nephrologist will discuss with you about your ideal and most effective therapy. Click here to read more about how the dialysis process works.

Whatever the cause of CKD is, it is important to note that the symptoms of the disease are similar in every stage, as well as all the needed measures to slow down the progression of the disease.

What do doctors recommend for patients in any stage of CKD

  • Tight control of blood pressure within target level: (130 mmhg systolic and 80mmhg diastolic)
  • Tight glycemic control for diabetics
  • Smoking cessation
  • Lipid lowering therapy
  • Regular exercise
  • Weight loss in case of obesity
  • Regular visits to a nephrologist
  • Medication intake and regular blood tests